Risk of CHD in Women

Young and middle-aged women experience only one-fifth the
incidence and mortality from CHD of men (16, 40, 94, 102, 139, 244,
255, 283). These rates are steeply age dependent, and rates in young
and middle-aged women lag behind those in men by about 10 years.
Reasons for the sex-dependent. differences are incompletely under-
stood, but this protective influence of female sex is partly due to
differences in cigarette smoking and other behavioral variables (6,
58, 103,127, 128, 150, 151, 166, 170,203,204,210,227,234,243,244,
255, 267, 270, 280).

During the 1950s and 196Os, when the previously reported large-
scale investigations of smoking and CHD were conducted, relatively
few women smoked, and on the average, those who did began at an
older age,.smoked fewer cigarettes, and inhaled less than men (261).
During the past two decades, women have begun to smoke cigarettes
at younger ages, and their cigarette smoking habits have become
more like those of men (261). Observations by a number of
investigators have shown that the incidence of CHD in recent years
in women who smoke cigarettes is far greater than the very low rates
that are observed in women who do not smoke, and the incidence of
CHD in women who smoke heavily may be similar to the incidence
in men.

To observe the effect of cigarette smoking in women more
specifically, studies have been performed to take account of poten-
tially confounding influences on the occurrence of CHD. Slone et al.
(244) in Boston observed cases and matched controls from a large
number of U.S. hospitals between July 1976 and December 1977.
During this l&month period, 55 cases of nonfatal MI were identified
in women under age 50 who had not used oral contraceptives within
the month prior to admission and who had not been under treatment
for heart disease or related disorders. The estimated relative risk for
smokers compared with nonsmokers was 6.8 (p <O.OOl). In light
smokers (1 to 14 cigarettes per day) the relative risk was 4.4, and in
heavy smokers (more than 35 cigarettes per day) the relative risk
was 21. The relative risk appeared as great in those who had not
experienced menopause as in those who had experienced menopause.
In those young women with no known risk factors other than
cigarette smoking, the data indicated that the smoking habit
accounted for 76 percent of the risk of nonfatal MI (244). This
magnitude of relative and attributable risk with smoking in other-
wise healthy young women is consistent with similar observations in
young men.

A subsequent report included cases observed through August 1978
with and without the following characteristics: obesity, diabetes
mellitus, abnormal blood lipids, hypertension, angina pectoris,
history of preeclampsia, coffee consumption, and oral contraceptive

101


(CC) use (227). Smoking was confirmed as a singularly strong risk
factor (Figure 10). Relative risk increased exponentially with the
number of cigarettes smoked, and the relative risk in younger
women was greater than in older women. A gradient of risk with
increasing level of cigarette smoking was also observed in subjects
who had one or more of the other risk factors. In those at the highest
level of risk, women smoking 35 or more cigarettes per day who had
one or more predisposing risk factors, the relative risk was 31.

A number of investigations have been performed to observe the
effects of OC use, and there is substantial evidence for interaction of
the smoking effect with OC use as well as other risk factors. These
data suggest that the biological effect of multiple risk factors,
particularly when combined with OC use, may be multiplicative for
the risk of CHD. Shapiro et al. (242) found that women who smoked
more than 25 cigarettes per day but did not use OCs experienced a
relative risk of MI of 7 in comparison with nonsmoking women who
did not use OCs. Nonsmokers who used OCs experienced a relative
risk of MI of 4.5. The women who combined both behaviors had a
relative risk of MI of 39. In a case-control study of factors related to
MI in nurses in the United States, Rosenberg et al. (226) reported
relative risks with OC use, smoking, and hypertension of 3,5, and 8,
respectively; however, in nurses with all three characteristics the
relative risk was 170.

Comparable results were observed in England by Mann, where the
relative risk for MI in women with major cardiovascular risk factors
(including cigarette smoking) who used OCs was up to 128 times that
of women free of these characteristics (169). The importance of
cigarette smoking to the incidence of MI in women has been
confirmed by other studies in England (211, 270), Sweden (16, 2791,
Scotland (2031, Finland (234, and elsewhere.

In addition to the excess risk of nonfatal MI and death from CHD,
sudden cardiac death in women has been observed to be strongly
related to the cigarette smoking habit (249, 254). However, the
relationship of angina pectoris to cigarette smoking is uncertain. As
in men, some studies have shown a positive relationship with
smoking (271), but other studies have found no significant difference
in the occurrence of angina pectoris between female smokers and
nonsmokers (16,40,203).

CHD incidence and mortality in women increase remarkably after
the menopause. Before the menopause, cases of CHD may be limited
largely to women who smoke (15, 16, 138). Furthermore, there is
evidence that the menopause occurs at an earlier age in women who
smoke than in women who do not smoke (129,270). Willet et al. (282)
observed a progressive increase in the risk of early menopause with
an increasing level of daily use of cigarettes, and cigarette smoking
was more closely related to early menopause than any other factor

102


0 Observed RR estimate. 30-44 yr
A Observed RR estamate, 45-49 y
0 Fltted RA estrnate

  20 -









   15 -
co
F
%
b
s
::   IO-
??
Y
F
4
E



  50 -








  10 -

30-44yr 0
/ B



8

0      1      2     3      4      5
Never    Ex-     1-14   15-24   25-34    -35
smoked   smoker

          CIGARETTES PER DAY

FIGURE lo.-Relation to relative risk of myocardial
       infarction to cigarette smoking, according to
         we

NOTE: DilTerence in slopea:x~~= 2.7,~ = 0.10.
SOURCE: Rceenbeg et al. wn.

considered. The evidence that a combination of cigarette smoking
with the use of oral contraceptives potentiates (multiplies) the
occurrence of CHD is strong, but the mechanisms are not adequately
understood. The use of noncontraceptive estrogens was not associ-
ated with an excess risk of MI (228). Furthermore, menopausal
estrogen therapy has been associated with a protective effect from
CHD death (231). There is evidence that both cigarette smoking and


progestins in oral contraceptives depress high density lipoprotein
cholesterol (HDL-C), and HDL-C appears to protect from CHD (13,
23, 35, 41, 59, 62, 74, 78, 122, 123, 213, 215, 265, 266, 269, 281). Those
with low levels of HDLC have been shown to suffer higher rates of
CHD than those with high levels of HDGC (see Interaction of
Cigarette Smoking and Other Risk Factors above).

Whatever the mechanism, it must be concluded that women who
decide to smoke assume a substantially increased risk of CHD, and
that the risk for women who smoke heavily approaches the risk of
CHD for men. The relative risk of cigarette smoking is greater in
younger women than in older women, and the relative risk increases
progressively with the number of cigarettes smoked. Women who
smoke have been observed to experience menopause earlier than
women who do not smoke, and this may also increase the CHD risk
for women who smoke. A synergistic interaction between cigarette
smoking and other risk factors for CHD has been demonstrated for
women, particularly for oral contraceptive use. More investigation is
required to evaluate this phenomenon; an astonishingly high rela-
tive risk of CHD occurs in women who smoke cigarettes and also
have other risk factors, including use of oral contraceptives.

Risk of Sudden Cardiac Death

The definition of sudden cardiac death @CD) is discussed in the
introduction to this section. In a number of studies, severe CHD has
been observed in a large proportion of the cases that have succumbed
toSCD (10,12,139,153,154,156,157,160,162,200,208,248).

In several epidemiologic studies, cigarette smoking has been even
more closely related to SCD than to CHD in general. After 24 years
of followup in the Framingham study (40, 1391, the risk of SCD in
cigarette smokers was found to be three times that in nonsmokers,
and a comparable relative risk was observed in the five-cohort
Pooling Project data (124, 251). Although the relative risk in young
men was greater than in older men, the relative risk was 2 even in
men aged 7@ to 79 in the Framingham cohort (40). In the Pooling
Project data, the IO-year incidence of SCD increased progressively
with the number of cigarettes smoked per day, analogous to the
relationships with the first major coronary event or with all CHD
deaths (124, 251). Other studies confirming the importance of
cigarette smoking in SCD include members of the Kaiser-Perman-
ente health plan in the San Francisco Bay area (681, black and white
men and women in Baltimore (156), men employed in the telephone
industry throughout the United States (llO), and men living in
Scandinavia (72, 220).

Other risk factors used to predict the occurrence of SCD include
hypertension, high relative weight, high serum cholesterol, left
ventricular hypertrophy by electrocardiogram, and alcoholism (50,

104


64, 68, 109, 137, 139, 149, 152, 153, 156, 173, 188, 209, 216). In
multivariate analysis of the combined Framingham and Albany data
for men aged 45 to 64, cigarette smoking emerged with the highest
level of statistical significance among five risk factors predicting
SCD (137).

Approximately half of those who experience SCD have preexisting
clinical evidence of CHD (109, 139, 153, 154, 220). In a study by the
Health Insurance Plan of Greater New York it was found that in
comparison with patients who stopped smoking, those who continued
to smoke after myocardial infarction or after the onset of angina
pectoris experienced twice the risk of death over the subsequent 4
l/a-year period of followup (242). Results supporting this observation
have been observed in some other studies (69, 141,155,233,238,250).

The results of numerous studies have consistently identified
cigarette smoking as a leading factor in SCD. This is true for men
and women, and the risk increases with the number of cigarettes
smoked per day.

Prospective Mortality Studies

The detailed epidemiologic studies of CHD incidence described
elsewhere in this section establish the close association between
cigarette smoking and the subsequent development of coronary
heart disease. The possibility that this association can be confounded
by other characteristics with which smoking is associated has been
intensively examined in these studies. The relationship between
cigarette smoking and CHD has been demonstrated to exist indepen-
dent of the presence of other risk factors.

Studies using CHD mortality as an end point can be performed at
a lower cost than can studies of the incidence of the disease. This
allows the inclusion of larger numbers of individuals in order to
examine the effects of smoking in larger segments of the population.
It also provides sufficient numbers of cases for detailed analyses of
the effects of dose, age, smoking cessation, and other variables of
interest. Studies examining the relationship between cigarette
smoking and subsequent CHD mortality are now available for a
variety of populations and include over 20 million person-years of
observation. In the 10 largest studies the results are remarkably
similar. Whether in the United States, Canada, the United Kingdom,
Scandinavia, or Japan, smokers as a group experience excess CHD
mortality that is approximately 70 percent above that of the
nonsmokers.

In the following paragraphs, the major studies that have prospec-
tively examined the relationship between cigarette smoking and
CHD mortality are discussed. The number of individuals followed in
these studies allows a detailed examination of the nature of this

105


relationship, including the changes in risk that occur with age, the
relationship between dose of cigarette exposure and CHD risk, the
effects of low tar and nicotine cigarettes, the risk of pipe and
cigarette smoking, and the benefits of cessation.

Overall CHD Risk for Men and Women

A number of major prospective studies have examined the
relationship between cigarette smoking and CHD mortality in men
and women. Under this heading, a description of the populations
studied and the findings for overall CHD risk in those populations
are presented. Under subsequent headings, the questions of the
differences in risk that occur with age, increasing dosage of cigarette
exposure, low tar and nicotine cigarettes, pipe and cigar smoking,
and the effects of cessation are examined on the basis of the evidence
from these prospective studies.

In the United States, Dorn initiated a study of U.S. veterans who
had served in the Armed Forces between 1917 and 1940 and who had
U.S. Government life insurance policies in force in December 1953.
This initial cohort of 293,658 persons was mailed a questionnaire in
1954, and the nonrespondents were followed up again in 1957.
Responses were obtained from 248,046 veterans, with an overall
response rate of 85 percent. Reports for 2 l/2 years (46') and 8 l/2
years (131) of followup were reviewed in detail in prior reports of the
Surgeon General. The N-year followup has been completed by Rogot
and Murray (224). Death certificates were located for 85,323 (98
percent) of those original questionnaire respondents who died.
Confirmation of the cause of death shown on the death certificate
was investigated by Dorn (46). Whenever a death occurred in the
United States, clinical confirmation concerning cause of death was
sought from the physician who signed the death certificate. A
response was obtained in 99 percent, and after review of the cause of
death based on clinical data, only 6 percent of the deaths were
reassigned to a cause different from that originally indicated on the
death certificate. This degree of confirmation is considered good.
Coronary heart disease mortality was 58 percent higher in cigarette
smokers than in nonsmokers (Table 8), and CHD accounted for more
excess deaths than any other cause of death.

In 1952, the 9-State study by the American Cancer Society was
initiated; 187,783 white males, aged 50 to 70, were followed for an
average of 44 months. There were 11,870 deaths. Of these deaths,
5,297 were due to coronary heart disease (96'). A highly significant
excess mortality was observed in smokers as compared with non-
smokers. The death rate for coronary heart disease was 70 percent
higher in smokers compared with nonsmokers (Table 8).

In late 1959 and early 1960, the American Cancer Society enrolled
1,078,894 men and women from 25 States in a prospective study that

106


TABLE 8.-Coronary heart disease mortality ratios, major
      prospective studies

Population/
Study

Size

         Mortality ratio

No. of          fzigarette
CHD deaths Nonsmoker   smoker

Comments

U.S.
veterans

ACS 9-&&e
study

Japanese in
29 health
districta

ACS 2SState
study

Canadian
veterans

British
physicians

Swedish
study

California
malesin

290,000 males    34,874       1.00      1.58


188,ooo males     5,297       1.00      1.70


122,000 males     3,351       1.00      1.71
143.000 females    2,653       1.00      1.78


358,@30 males    10,771       1.00     1.90-2.55
483,000 females    4,048       1.00       o

~78,OCKl males     3,405       1.00


34,000 malee     3,191       1.00
6,195 females     179       1.00

1.60

1.62

27,ium males      916       1.00      1.70
28,000 females     457       1.00      1.30

68,cQo males     1,718       1.00      1.60

Male data for two
levels of smoking
intensity, see Table
12; `female data
available by age and
amount smoked only,
see Tables 9 and 14

`Female data avail-
able by amount
smoked only, see
Tables 9 and 12

Swiss
physicians

3,149 males      280       1.00     xX3-2.18

Data available by
amount smoked only,
see Table 12

was the largest of its kind ever conducted. All segments of the
population were included, with the exception of groups that could
not be easily traced. An initial demographic questionnaire recorded
height, weight, detailed information concerning smoking (types of
tobacco used, number of cigarettes smoked per day, inhalation, age
at which smoking began, brand of cigarettes used), and other
variables that might influence mortality. Hammond reported cause-
specific mortality for the initial followup through September 1963
(97.4 percent successfully traced) on all those aged 35 to 84 at the
time of enrollment (93). In men, 1,639,211 person-years of experience
were observed, and in women, 2,125,360 person-years of experience
were observed. Death certificates were obtained in 97.9 percent of
the 25,895 deaths. CHD mortality ratios in male cigarette smokers

107


compared with those who never smoked regularly varied from 2.81
in men aged 45 to 54 to 1.24 in men aged 75 to 84 (Table 9). Ratios for
women were 2.00 and 1.19 for age 45 to 54 and 75 to 84, respectively.
In the 6year followup reported by Hammond and Garfinkel (94),
there was a total of 28,446 deaths. Using the death rates of
nonsmokers as the standard, over 11,590 excess deaths were
attributable to smoking. Coronary heart disease accounted for 46
percent of the excess deaths in men and 40.6 percent of the excess
deaths in women.

A study of California men in various occupations was begun in
1954, and 68,153 men aged 35 to 64 were followed for mortality
through December 1962 (234). Smokers included current as well as
ex-smokers. Nonsmokers were all men who had never regularly
smoked cigarettes for even 1 year, and pipe and cigar smokers were
included in this group. A total of 4,706 men were identified. The
mortality ratio for CHD was 1.6 (60 percent excess CHD mortality) in
smokers as compared with nonsmokers.
San Francisco longshoremen were studied by Paffenbarger et al.
(205); 3,686 men aged 35 to 74 were examined in 1951 and followed
for 22 years. A total of 1,270 deaths were observed during 55,635
person-years of observation. After adjusting for difference in age,
systolic blood pressure, and level of activity, the CHD mortality ratio
for those smoking 20 cigarettes or more per day was 2.09 relative to
those subjects who smoked fewer cigarettes or none.

Gillum and Paffenbarger reported CHD mortality from followup of
13,728 university students examined between 1939 an< 1950 (77).
CHD morbidity followup was observed in 8,852 who had returned
self-administered questionnaires in 1962, 1966, or 1972. Four control
subjects were randomly assigned to each of the 98 cases of fatal CHD,
78 cases of myocardial infarction, and 49 cases of angina pectoris.
Fatal CHD, MI, and angina pectoris were strongly associated with
smoking history; relative risks were near 2.5. Association with fatal
CHD, or with MI, or both, was also apparent for a family history of
CHD, weight, height, and systolic blood pressure.

The Canadian Department of National Health and Welfare
initiated a study in 1955 of smoking and health in disability
pensioners, principally veterans of World Wars I and II. Best
reported the results of a 6year followup in 1966 (17). The 78,000
Canadian men were aged 30 to 90 at the onset of the study. Smoking
habits were determined at the start of the study. Nonsmokers were
respondents who had never smoked. Ever smokers were those who
had smoked at least 100 cigarettes during their lifetime or 10 cigars
or 20 pipefuls of tobacco. Current smokers were those who reported
smoking at the start of the study. Ex-smokers were those who had
smoked previously, but had stopped smoking at the start of the
study. During the (i-year followup, 9,491 deaths were observed, of

108


TABLE 9.4ronary heart disease mortality ratios and
      rates, by age and smoking habit, prospective
       studies

Study

Mortality ratio and (rate)' by age

AC% 25.Stat.e

Male nonsmoker
Male smoker
Female nonsmoker
Female smoker

35-44      45-54      5.5-64      65-74      7&&34
- -    - ___
l.oo-1'     1.oowio~     l.ow42)    1.ooC1400)    Loo(3132)
- (148)    2.81(422)    l.a4@96)    1.45@25)    1.24@71)
1.00       l.WW     l.oow3)    1.00(653)     1.00(19733
-      2.00(66)     1.6%275)    1.44041)    1.19@49)

U.S. veterans

Nonsmoker or
occasional only
fzigarettes only

Japanese in 29 health
diitricts

Male nonsmoker
Male smoker
Female nonsmoker
Female smoker
ACS 9-E%.& *

Nonsmoker
Smoker

35-44

Loowl)
4.44@0)

1.W~)     l.Cux501)    1.0@1015)
7.00(353)     1.60@601    1.6of1659r

1.01X2216)
1.20(2683)

4049        50-m        60-69        70+
1.oc@.0)       l.OOw3.3)      l.OO(105.5)     l.OO(189.6)
3.09a4.7)      1.4268.8)      1.62U70.7)     1.71t323.8)
l.OLX6.1)       l.OOC?3.6)      l.oo(79.5)      l.OO(lc9.4)
1.46@.9)       1.7X41.2)     1.54w2.5)     1.44(157.9)

45-54      5.564      65-74

75-M

50-54

1.00@71)
1.92@21)

55-59        60-64

Loowl)      1.00(733)
1.650301)      1.66(1219)

65-69

l.oow?47)
1.41(1759)

British physicians, male
Nonsmoker
currenf cigarettee only

British physicians, female
Nonsmoker
Smoker 1-14 cigarettes
     15-24 ci&B
     25+ cigarettes

<65                 265
l.ow39)               l.ax1655)
2.19(413)                1.37(2259)


1.00(31)                 l.ooC511)
1.41(44)                0.78@02)
2.54(79)                2.1&1117)
2.74@5)                2.76(1411)

Canadian veterans        55-59      60-64      6569      70-74      75-79
                         ~ ~   ~ -

Nonsmoker            1.00       1.00       1.00       1.00       1.00
CigaFettes OdY         1.90       1.61       1.36       1.79       1.45

Swedish pmepective         16-39        40-49        50-59        6@69
Nonsmoker             1.00         1.00         1.00         1.00
Male smoker, cigs only      -          2.60         1.70         1.70
Female smoker           -          -          2.60         1.10

Swiss physicians          35-54        5.5-G        66-74        75+
Nonsmoker            1.00         1.00         1.00         1.00
Heavy smoker *          2.30         2.20         1.90         1.00

C!difomia males in 9        3&u      4ti51        5s64        6549
OCCUpatiOnS

Nodmoker             1.00
Smoker               6.24


' Bate per 100,COO. anlam otherwIse stated.
n Number of deaths tna small to compute a ratio.
' Heavy smoker: one or more path per day.

1.00         1.00         1.00
2.95         1.56         1.24

which approximately 2,000 were attributed to coronary heart
disease. Smokers experienced a death rate 68 percent higher than

109


that of nonsmokers. The excess mortality was due mainly to
cardiovascular disease, with coronary heart disease alone accounting
for 36 percent of the excess. The death rate due to coronary heart
disease in smokers was 60 percent higher than the death rate in
nonsmokers (Table 8).

In 1951, a study of mortality in British physicians was initiated.
The results were reported by Doll and Hill (44) and subsequently by
Doll and Pete (45) and by Doll et al. (43). A total of 34,400 men
responded to the questionnaire (69 percent response rate). Followup
questionnaires were sent in 1957, 1966, and 1972. Twenty-year
mortality through October 1971 was reported in 1976 (45). Virtually
all of the sample had been traced, and 10,072 deaths were identified.
Nonsmokers were defined as those who had never smoked as much
as one cigarette per day for as long as 1 year. Smoking status was
updated using the information from followup questionnaires. Coro-
nary heart disease accounted for 3,191 of the deaths. Information
from the first questionnaire was related to the deaths occurring in
the first 7 years, information from the second questionnaire to
deaths in the next 8 years, and information from the third
questionnaire was related to deaths in the last 5 years of the
followup period. The death rate for smokers of all forms of tobacco
was 37 percent higher than the death rate for nonsmokers.

Results of the 22-year mortality followup of female British
physicians were reported recently (43). Among 6,194 respondents
there were 1,094 deaths. Coronary heart disease was the underlying
cause of death in 179. Among smokers, excess mortality was
observed only for those smoking 15 or more cigarettes per day, but
for these women the relative risks exceeded 2. The coronary heart
disease mortality of all female smokers was only 35 percent of that of
all male smokers. Those women who smoked more heavily (15 or
more cigarettes per day) experienced CHD mortality that was 67
percent of that of men who smoked more than 15 cigarettes per day.
Further analyses indicated that these female smokers had a lower
cumulative smoking exposure than the male smokers; the female
smokers had begun smoking at later ages and smoked fewer
cigarettes, and fewer reported inhaling cigarette smoke. The CHD
deaths among the female smokers were too few for more detailed
analysis of the risk at levels of smoking behavior comparable to the
most intense male smokers.

Examinations were given and questionnaires administered to
18,403 British civil servants working in London (205). Blood pres-
sure, plasma cholesterol, blood glucose, height, weight, and relevant
data were collecfecl in a standardized fashion. During the U&year
followup there were 1,657 deaths, of which 704 were due to coronary
heart disease. Grade of employment was significantly related to
death from coronary heart disease; those at the highest grades

110


(administrators and professionals) experienced the lowest rates.
However, at each grade of employment cigarette smokers experi-
enced higher mortality than nonsmokers. The mortality of ex-
smokers was similar to that of nonsmokers.

Grundy (89) reported the relationships of smoking habit and
worksite exposure to carbon monoxide for 4,924 steelworkers in
Ebbwvael, Wales, who were examined in 1964. After 10 years, 99
percent of the population surveyed was traced and 740 deaths were
recorded. The total mortality and CHD mortality were higher than
average for England and Wales. The smokers (73 percent of the
sample) experienced a coronary heart disease mortality that was 80
percent higher (relative risk 1.8) than that of nonsmokers. Occupa-
tional exposure to carbon monoxide appeared to play a negligible
role, in comparison with the importance of cigarette smoking, for
coronary heart disease mortality. The high smoking rate in this
population explained a substantial part of the excess mortality of
this population compared with the average mortality for England
and Wales.

In 1963, a probability sample of Swedish men and women aged 18
to 69 was surveyed by Cederlof et al. (31), and mortality was observed
during the subsequent 10 years through December 1972. There were
25,444 male respondents (93 percent) and 27,342 female respondents
(95 percent). In 1969, a followup questionnaire of a subsample
indicated that smoking habits had not changed substantially since
1963 in the majority of those surveyed; for example, 78 percent of
men and 63 percent of women who reported smoking 16 or more
cigarettes per day in 1963 reported the same cigarette habit in 1969.
During the N-year followup, a total of 5,655 deaths were ascer-
tained. Overall coronary heart disease mortality was 70 percent
higher in male cigarette smokers and 30 percent higher in female
cigarette smokers than in nonsmokers (Table 8). The possibility of
confounding by other factors was evaluated. For univariate analysis,
lower income and listing with the Swedish Alcohol Registry were
associated with significantly higher CHD mortality. (In Sweden,
violators of laws related to the use of alcohol, e.g., public drunken-
ness, drunk driving, illegal alcohol sales, are required to be
registered.) However, cigarette smokers in each of these groups had
significantly higher CHD mortality than never smokers, and the
differences were particularly marked at higher levels of cigarette
consumption. The CHD relative risks were also significantly higher
for cigarette smokers within the high income group, among rural
residents, and among those not listed in the Alcohol Registry.

In the Stockholm prospective study, risk factors for ischemic heart
disease were evaluated in 3,486 men and 2,738 women who were first
examined in 1961 through 1962 (22). During a 14 l/2-year followup,
a total of 694 deaths were observed, of which 43 percent in men and

111


31 percent in women were attributed to ischemic heart disease. Of
235 ischemic vascular deaths in men, 189 were attributed to
myocardial infarction. In univariate and multivariate analyses,
cigarette smoking was signiticantly and independently related to the
risk of ischemic vascular death in both sexes.

In 1955, a survey on the smoking habits of 3,749 Swiss physicians
was initiated. The first reported findings (252) after 9 years of
observation were similar to the findings in the British physicians
study of Doll and Hill (44). More recently published data, baaed on 18
years of followup (90), recorded 1,212 deaths among those physicians
who completed questionnaires during the original survey and for
whom complete information concerning cause of death was avail-
able. A total of 280 coronary heart disease deaths (59 nonsmokers
and 221 smokers) were reported. CHD mortality ratios increased
with increasing number of cigarettes per day. Light smokers (10 or
fewer cigarettes per day) had a mortality ratio of 1.33, increasing to
2.18 with the heaviest amount smoked (35 or more cigarettes per
day). Mortality for CHD among smokers tended to be greater in the
younger age groups than in the older age groups.

Hirayama has reported followup at 8,10, and 13 years for 122,261
men and 142,857 women over 40 years of age who were residents in
29 health districts in Japan (111-126). There was an overall 95
percent participation rate, and ascertainment of cause of death was
virtually 100 percent. In the 13year followup, over 3 million person-
years of risk and 39,127 deaths (22,946 in men and 16,181 in women)
were observed. Heart disease was certified in 3,351 men and 2,651
women. At the time of the baseline survey, the proportion-of smokers
was 76 percent in men and 10.5 percent in women. Mortality ratios
for smokers were 1.7 for men and 1.8 for women. The possibility of
confounding by other factors was evaluated through crossclassifica-
tion of smoking by social class, consumption of meat and milk, and
alcohol consumption. Higher coronary heart disease mortality was
observed with higher social class and among those consuming more
meat and milk. Alcohol intake was inversely related to coronary
heart disease mortality. At both high and low levels of these
characteristics, however, the risk of death from CHD among smokers
remained higher than among nonsmokers. The proportion of coro-
nary heart disease mortality attributed to cigarette smoking in this
population was 34.3 percent for men and 9.5 percent for women.

CHD mortality, as well as CHD incidence, is clearly much higher
in cigarette smokers than in nonsmokers. This excess mortality
occurred uniformly in each of the major prospective studies. It also
occurred in populations of markedly different ethnic background
and geographical location. The relationship also persisted when a
number of other confounding variables were taken into account. The
risk was somewhat lower for women, but in those groups of women

112


whose smoking habits approximated those of men, the CHD death
rates were much closer to those of men.

Impact of Cigarette Smoking on Coronary Heart Disease
Mortality With Increasing Age

Coronary heart disease mortality increases with increasing age in
both cigarette smokers and nonsmokers. The question of the
magnitude of the CHD risk due to smoking for different age groups is
one that has important public health impact for advising individuals
at different ages about the risks of smoking and the benefits of
cessation. In several of the prospective mortality studies, the
question of the magnitude of the risk of dying of coronary heart
disease at different ages in smokers and nonsmokers has been
examined.

Table 9 details the coronary heart disease death rates and
mortality ratios for different age groups of smokers and nonsmokers
in each of the prospective studies reporting these data. As can be
seen from this table, the CHD mortality ratios for cigarette smokers
compared with nonsmokers decline with increasing age. However,
the decline in the ratio is the result of the rapid rise in CHD
mortality rates with age in nonsmokers, and the absolute difference
between the death rates of cigarette smokers and nonsmokers
increases with increasing age. Thus, the excess risk is actually
numerically greater in older populations than in younger popula-
tions, and the reduction in mortality ratio is an artifact of the fact
that coronary heart disease is responsible for such a large part of the
mortality of the older age groups in the United States.

Figures 11 (men) and 12 (women) present the relationships of CHD
mortality and age for nonsmokers and smokers of various number of
cigarettes per day. The risk for the nonsmoker increases steadily
with increasing age, but with each increment in number of cigarettes
smoked per day, there is a clear increase in CHD risk prior to age 70.
The shape of the curve with increasing age remains similar with
increasing number of cigarettes smoked per day, and the net effect is
consistent with cigarette smoking increasing the apparent "CHD
risk age" of the individual by 5 to 15 years.
The decline in the mortality ratio with increasing age found in the
prospective mortality studies is consistent with the risk factor
relationships found in the incidence studies. In these studies,
cigarette smoking is responsible for a relatively larger proportion of
the coronary heart disease occurring in younger populations and a
smaller percentage of the total coronary heart disease occurring in
older populations.

113


5ooo





45OQ





4000





3500





3000





2500





2ooo





1500





1000





500

No. of cigarettea
smokedperday

10-1s

None

t          I          I          I          1
40         50         60         70         60

                 YEARS

FIGURE ll.-CHD death rates (per 100,000), by age and
       number of cigarettes smoked per day, males
SOURCE: Derived from the ACS 25-Stat.e study (93.

Dose-Response Relationships

The large number of deaths observed in the prospective mortality
studies allow a detailed examination of the relationship between the
"dose" of smoke exposure and subsequent coronary heart disease
mortality. The simplest measure of dose is the number of cigarettes
smoked per day; however, the dose of smoke received by a person

114


No. of cigarettes
smoked per day

2000




1400


1300


1200


1100


1000


900


600


700


600


500

NOIW









2s39









lo-19

40         50         60         70         60

                 YEARS

FIGURE lZ.-CHD death rates (per lOO,OOO), by age and
       number of cigarettes smoked per day, females
SOURCE Derived fmm the ACS %-State study WY.

would also be increased in those persons who inhaled deeply
compared with those individuals who did not. The duration of the
cigarette habit is also a measure of the dose of exposure; those
persons who began to smoke earlier in life would have a greater
cumulative exposure to cigarette smoke at any given age than those
persons who began to smoke later in life. Several of the major
prospective studies have examined these questions; the data are

115


TABLE lO.-Coronary heart disease mortality ratios by
      inhalation characteristic, prospective studies

Study

sex

Nonsmoker

Inhalation characteristic

Light

None

Swedish       Male                 1.00        1.8       1.6      1.2
           Female                1.00        1.6       1.2      1.7'

                                          YeS         NO

British        Male       <65        1.00          2.2         1.4
physicians              >65        1.00          1.5          1.3

None-alight   Moderate-deep

ACS          Male       4534
25-.%&e               55-64
                    65-74
                    n-84

Female      4.544
         5544
        65-74
         75.84

1.00
1.00
1.00
1.00

1.00
1.00
1.00
1.00

2.67         3.17
1.83         2.01
1.31         1.63
1.29         1.20

1.82         2.15
1.61         1.89
1.30         1.78
1.13         -2

L Number of deaths too small for statistical reliability.
`Number of deaths tax small to compute.

presented in Tables 10, 11, and 1`2. Table 13 provides data from two
studies that examined the risk of coronary heart disease mortality
by length of time smoked. In general, they show that the more total
years of smoking exposure the greater the overall risk of CHD
mortality.

In the study of Canadian veterans, a progressive dose-response
relationship was observed with number of cigarettes smoked per day.
The CHD mortality ratio increased from 1.55 in those smoking 1 to 9
cigarettes per day to 1.78 among those who reported smoking 20 or
more cigarettes per day. A similar relationship was found in the
American Cancer. Society 9-State study, where the excess CHD
mortality rate varied from 29 percent in smokers of 1 to 9 cigarettes
per day to 140 percent in smokers of 41 cigarettes or more per day.

In the American Cancer Society 25-State study, the number of
CHD deaths was large enough to conduct a detailed examination of
the relationship between the dose of cigarette smoke exposure and
the subsequent coronary heart disease mortality. The mortality
ratios for males in the group 45 to 54 years of age increased from
2.35 in those who smoked 1 to 9 cigarettes per day to 3.35 in those
who smoked 40 or more cigarettes per day. In the next oldest age
group, those 55 to 64 years of age, the mortality ratio increased from
1.54 in those who smoked 1 to 9 cigarettes per day to 2.13 in those
who smoked 40 or more cigarettes per day (Table 14). The mortality
ratio also increased with depth of inhalation. In the 45- to 54-year-old

116


TABLE il.-Coronary heart disease mortality ratios by age
      began to smoke, prospective studies

Study          Age

Nonsmoker
ratio

        Smoker
Mortality ratio by age of initiation

us. veterans                        5 14     1519      W24    2%

              55-64        1.00       1.96      1.64       1.65     1.56
              65-74        1.00       2.03      1.66       1.54     1.55

ACS 2.5State                       <14       15-24      2%

Males          45-54        1.00        3.47        3.11        2.37
            55-64        1.00        2.08        1.99        1.70
            6&74        1.00        1.54        1.62        1.17

FemallX3         45-54        1.00        -'        2.03        2.00
            55-64        1.00        -         1.64        1.74
            65-74        1.00        -         -        1.36

Males                    1.00        3.65        1.90        1.67

Swedish                          516       17-16       219

M&9                    1.00
          .
Females                   1.00


' Number of deaths tao small to calculate ratio.

1.90        1.70        1.70
2.00        1.10        1.30

age group, the mortality ratio increased from 2.67 in those who
inhaled not at all or only very slightly to 3.17 in those who inhaled
moderately or deeply (Table 10). There was also a consistent dose-
response relationship when the age at which the individual started
smoking was considered. The younger the age at which regular
smoking began, the greater the mortality ratio. In the 45-54 age
group the mortality ratio increased from 2.37 in those who began
smoking at age 25 or older to 3.47 in those who began smoking prior
to age 15 (Table 11).

For women, the excess mortality in the American Cancer Society
25State study generally paralleled the dose-response relationship
observed in men, but the CHD deaths were too few for evaluation of
the risk related to the age at which smoking was begun.

A similar relationship was demonstrated in the study of California
men in various occupations. The mortality ratio increased from 1.39
for those men who smoked half a pack per day to 1.74 for those who
had smoked 1 l/2 packs or more per day. Mortality ratios increased
with the duration of smoking from 1.05 in those who had smoked
from 1 to 9 years to 1.77 in those who had smoked 20 years or more.
The study of British physicians also examined the question of a
dose-response relationship. They found a steady increase in CHD
mortality with increasing number of cigarettes smoked per day. The
death rate from ischemic heart disease increased from 501 per
100,000 in those who smoked 1 to 14 cigarettes per day to 677 per

117


TABLE 12.-Coronary heart disease mortality ratios by
      amount smoked, prospective studies

Study

      M&S                   Females

cigs/bY         Ratio       cigs/bY       Ratio

U.S. veterans

Nonsmoker        1.00
l-9             1.24
l&20           1.56
2139           1.76
40+           1.94

ACS 9-State






JapeSe

Nonsmoker        1.00
l-9             1.29
lo-20           1.89
21-40           2.15
41+            2.41

Nonsmoker        1.00
1-14            1.59
15-24           1.79
25-49           2.11
50+            2.82

(For female data,
see Table 9)

ACS 25State

Nonsmoker
1-19
20+

1.00
1.90
2.55

(For female data,
see Tables 9 and 14)

Canadian veterans

Nonsmoker        1.00
l-9             1.55
10-20           1.58
21+            1.78

British physicians






Swedish






California
mupationa



Sti physicians

Nonsmoker        1.00        Nonsmoker        1.00
1-14            1.47         1-14            0.96
15-24           1.58         1624 f        2.20
25+            1.92        25+            2.12

Nonsmoker        1.00         Nonsmoker        1.00
1-7             1.50         l-7             1.20
8-15            1.70         l&15            1.60
16+            2.20        16+            3.00

Nonsmoker        1.00
about 112 pk       1.39
about 1 pk        1.67
about 1 l/2 pk      1.74

Nonsmoker        1.00
l-10            1.33
l&19           1.42
29-34           1.77
350rmOlV        2.18

100,000 in those who smoked 25 or more cigarettes per day. Depth of
inhalation was analyzed after adjusting for age and amount smoked.
Those responding that they did inhale experienced a 57 percent
higher mortality rate than those responding that they did not inhale.
A dose-response relationship was also reported in the U.S.
veterans study, the study of mortality in northeast England, the

118


TABLE 13.-Coronary heart disease mortality ratios by
     number of years having smoked, prospective
        studies

Study

             Number of years having smoked

Nonsmoker  < 5         5-9   lo-14       15-19  2&29  3cM9  240

Canadian
veterans    1.00     1.4         1.7    1.5         1.7    1.6    1.5    1.6

                    l-9             lo-19           20+

California
occupations   1.00         1.05             1.13             1.77

TABLE 14.-Coronary heart disease mortality ratios, males
      and females, by age and amount smoked, ACS
      %-State study

Number oi       4.544       55-64       65-74       75-64

cigarettes/day    M F     M F     M F     M F

Nonsmoker     1.00   1.00    1.00   1.00    1.00   1.00    1.00  1.00
l-9         2.36   9.94    1.54   1.26    1.26   1.10    1.17  -'
E-19        3.09   2.00    1.92   1.64    1.61   1.42    1.39   -
2%39        3.11   2.67    2.04   2.01    1.56   1.65    1.11   -
40+         3.35   -    2.13   -     -    -     -   -

' Number of deaths too small to wmpute.

Swedish probability sample study, the Stockholm prospective study,
and the study of 29 health districts in Japan. Mortality from CHD in
the Whitehall study was higher in inhalers than in noninhalers, but
the relative risk was reduced after adjusting for cigarette consump
tion and tar yield. Among inhalers, the risk increased with the
amount smoked; this trend was less evident in those not inhaling.

Thus, in those studies that have had an adequate number of deaths
to examine the question of a dose-response relationship between
cigarette smoking and death from coronary heart disease, a clear
dose-response relationship has been demonstrated for the number of
cigarettes smoked per day, depth of inhalation, age at initiation of
the smoking habit, and total duration of the smoking habit. The risk
of coronary disease mortality is lower with fewer cigarettes smoked
per day, but the evidence presented in the prospective mortality
studies does not suggest a threshold for this effect. There is no
evidence to suggest that any level of cigarette smoking is safe with
regard to coronary heart disease risk.

119


Low Tar and Nicotine Cigarettes

There has been a major change in the tar and nicotine yield of the
cigarettes being smoked by the U.S. population over the last 30
years. The impact of this decline in tar and nicotine yield on the risk
of developing coronary heart disease in individuals smoking lower
yield cigarettes has been examined in detail in the 1981 Report of the
Surgeon General The Health Consequences of Smoking: The Chang-
ing Cigarette (262). There are essentially no epidemiological data on
the risk of very low yield cigarettes (those below 5 mg of tar). The
American Cancer Society 25-State study did, however, address the
relative risk of those who smoked cigarettes with varying yields of
tar (95). Groups were matched for age, race, number of cigarettes
smoked per day, age at which smoking began, place of residence,
occupational exposures, education, and history of lung cancer or
heart disease. CHD mortality was calculated for two 6-year periods
(196CL1966 and 1966-1972) for those smoking low, medium, or high
tar and nicotine cigarettes. The men and women (both in early and
late periods) who smoked cigarettes with high tar and nicotine yield
experienced higher CHD death rates than those who smoked low tar
and nicotine cigarettes (Table 15). Additional analyses were per-
formed after further matching of the groups with respect to history
of stroke; diabetes mellitus; hypertension; usual amount of exercise;
obesity; consumption of aspirin, tea, coffee, and alcohol; and occupa-
tion. Although this procedure resulted in fewer matched subjects,
the results were comparable to the analyses above; CHD mortality in
the low tar and nicotine cigarette smokers was 86 percent of that of
the high tar and nicotine cigarette smokers. However, this slight
reduction in CHD mortality associated with smoking low tar and
nicotine cigarettes disappeared if an increase in the number of
cigarettes smoked per day occurred. Those smokers of low tar and
nicotine cigarettes who smoke between 20 and 30 cigarettes per day
experienced a 10 percent higher coronary heart disease mortality
than did smokers of 1 to 19 high tar and nicotine cigarettes. In
addition, a comparison of matched subjects who never smoked
regularly with those who smoked low tar and nicotine cigarettes
revealed that the low tar and nicotine cigarette smokers experienced
a 66 percent higher coronary heart disease mortality rate.

Data from the Framingham study on the incidence of coronary
heart disease (30) have not shown a lower CHD risk among filter
smokers compared with nonfilter smokers.

Data from the Whitehall study have been published that examine
tar yield by number of cigarettes smoked per day in inhalers and
noninhalers for CHD mortality. This is presented in Table 16. While
no clear pattern is evident for noninhalers, among inhalers there
was a tendency for the highest CHD rates to be seen in those
smoking cigarettes with the highest tar yield (108). In a recent study

120


TABLE 15.-Adjusted number of coronary heart disease
      deaths and mortality ratios during each of two
      periods of time, by sex and by tar and
      nicotine content of cigarettes usually smoked

sex

Period '

High tar      Medium tar     Low tar
and nicotine     and nicotine    end nicotine

Male
Female
Female

Total

Male
Male
Female
Female

Total .

Adjusted number of CHD deaths

696.5         632.5         645.6
336.0         345.6         274.2
318.7         277.5         257.4
265.6         228.0         215.5

1.616.8        1,#3.3        1.392.7

      Mortality ratios

1.00          0.91          0.93
1.00          1.03          0.82
1.00          0.87          0.81
1.00          0.86          0.81

1.00          0.92          0.86

`Period 1: 1960-1966; Period 2: 1966-1972
SOURCE: Hammond et al. wh

TABLE le.-Ten-year coronary heart disease mortality per
       hundred (and number of deaths) standardized
      for age and employment grade, according to
      cigarette consumption and tar yield, Whitehall
       study

                 Inhalers                     Noninhalers

        l-S/day   1@19/day   > m/day     I-9/day   1&19/day   > 2O/day
         ~ ___ ___ ___ ___ ~

Tar (m&i@ Rate No.   Rate No.   Rate No.    Rate No.   Rate No.   Rate No.

18-23      2.68  (14)   5.63  (71)   6.60  (101)    3.94  (14)   4.91  (17)   6.05  (20)
24-32      3.81   (7)   6.57  00)   6.23  (36)    1.78   (3)   9.03  (10)   4.27   (6)
2%       7.42  CD)   6.47  (37)   7.84  (10)    5.06   (4)   4.75   (4)   0.00   (0)

Total      4.29  (44)   5.98  (138)   6.56  (147)    3.46  (21)   5.73  (31)   5.16  (26)

NOTE: Rate for lifelong nonsmokers of cigarettes = 2.75 (70).
SOURCE: Higgenbottam et al. (108.

(240), tar and nicotine content of the cigarettes was documented;
those men who smoked low yield cigarettes did not have a lower risk
for myocardial infarction than those smoking higher yield cigarettes.
The relative risk of developing coronary heart disease in persons
smoking low yield cigarettes and persons smoking high yield
cigarettes is further confounded by the possibility that those who

121


TABLE 17.-Coronary heart disease mortality ratios for
     male cigarette, pipe, cigar, and mixed pipe
     and/or cigar smokers, prospective studies

Study            Nonsmoker


U.S. veterans'         1.00

    Mortality ratios
Cigarette    pipe    aw   Mixed pips and/
smoker     smoker   smoker  or cigar smoker


1.58       1.02      1.12

ACS 9-Stat.e          1.00         1.70        -      1.28

Swedish

1.00         1.70       1.40

ACS 25State'         1.00       1.90-2.55      1.08

British physicians       1.00

' Smoker group are "pure" smokers only.
' Age 5664 only.

1.62                        1.03

smoke low yield cigarettes may smoke greater numbers of cigarettes
per day or may alter the manner in which they smoke those
cigarettes to increase the yield from the cigarette. The available data
are conflicting concerning a possible reduction in risk of CHD for
those smoking the lower yield cigarettes; further evidence is needed
before this question can be definitively answered.

Pipe and Cigar Smoking

A number of studies have addressed the question of.the relative
risk for CHD from smoking pipes and cigars compared with
cigarettes. Those prospective mortality studies containing data that
address this question are presented in Table 17. In general, the risk
for coronary heart disease mortality of smoking pipes and cigars is
substantially lower than the risk of smoking cigarettes. This is
generally felt to be due to the tendency of pipe and cigar smokers not
to inhale smoke into the lung. If this is the mechanism of this lower
risk, then the tendency of those who switch from cigarettes to pipes
and cigars to continue to inhale the smoke may minimize or
eliminate the reduction in risk for coronary heart disease that might
be expected after switching to pipes and cigars from cigarettes.

Cessation

Whether the excess coronary heart disease mortality that occurs
with cigarette smoking decreases over time following cessation of
cigarette smoking is a question of great importance for those
individuals who are currently smoking cigarettes. Data from the
prospective mortality studies that have examined this question are
presented in Table 18.

122


TABLE 18.-Cessation of smoking and coronary heart
     disease mortality ratios, prospective studies

Study             Continuing smoker

Eksmoker

U.S. veterana

Swedish males
     females

ACS 25&&e

Canadian veterans

British physicians
males

Japanese males in
29 health dietricte

  1.58              1.16

  1.70              1.50
  1.30              1.50

l-19' 20+        1-19 2O+
1.87   2.06         1.26    1.62

  1.60              1.46

1.62              1.29

1.71

1.34

TABLE 19.-&essation of smoking and CHD mortality
      ratios, by length of time off cigarettes and
      number of cigarettes smoked daily, ACS 2!5-
      State study, 6year followup

Years stopped smoking

Amount smoked per day

l-19          20+

None, current smoker                1.87          2.06
Le3sthan1                      2.00          2.13
1-4                           1.43          2.00
5-9                          1.44           1.45
10 or more                      0.99          1.35
All ex-emokers                    1.26          1.62

In the American Cancer Society 25-Stat.e study, the mortality
ratios in former smokers compared with continuing smokers were
progressively lower with increasing intervals of smoking cessation.
For those who had smoked less than 20 cigarettes per day, the CHD
mortality after 10 years of cessation was comparable with that of
those who had never smoked regularly. However, for those who had
smoked 20 or more cigarettes per day, the CHD mortality rate
remained 35 percent higher even after 10 years (Table 19).
The British study of physicians also conducted a detailed analysis
of the effects of cessation. The relative risk for males 30 to 54 years
of age was 1.9 for those who had discontinued smoking for less than 5
years, but it was 1.3 for those who had discontinued smoking for 5 or
more years. Those who discontinued smoking for 15 years or more
had a relative risk that remained slightly above 1. Those aged 30 to

123


TABLE 20.PHD mortality ratios by length of time off
       cigarettes

Study

           Mortality ratios

"ke   Nonsmoker      Yeare off cigarettes         comments

                       <5    5-9   l&14 5+

British        3s54    1.00     1.9     1.3     1.4     1.3
phyaiciam     5544    1.00     1.9     1.4     1.7     1.3
e@yr foump)  85+     1.00     1.0     1.3     1.2     1.1

                        <IO        >lO

Swedish m&n          1.00       1.50         1.00
(l@yr followup)

Japanese males
in29health
dietrict3
(1Csj-r folbJwup)

1.00





1.00

54        25

1.15         0.90





2.10         1.82

Smokers who consumed
<2oo,ooo cigaretteal
lifetime


Smokers who consumed
>2wloo cigarew/
lifetime

64 had a relative risk of 1.3 after 15 years, while those 65 and over
had a relative risk of 1.1 (Table 20).

The Swedish national probability sample study examined former
smokers who had stopped in the 10 years prior to 1963. A relative
risk of 1.6 existed for those who had smoked 20 years or more prior to
quitting, but the relative risk was 0.9 for those who had-smoked less
than 20 years before quitting. Those at younger ages had greater
residual relative risks than those in the older age groups. Among
those who had stopped smoking 10 or more years prior to the
beginning of the study, no significant excess risk of coronary disease
was observed. The results in women were consistent with those in
men, but the cases were too few for detailed analysis (Table 20).

In the Japanese study of 26 health districts, former smokers
exhibited relative risks that were related inversely to the time since
smoking cessation; the residual risk was directly proportional to the
number of cigarettes smoked prior to quitting.

Data from the X-year followup of U.S. veterans provides informa-
tion on CHD mortality for ex-smokers by the number of cigarettes
smoked per day (Table 21). Those ex-smokers with the lowest
smoking exposure levels as measured by the number of cigarettes
consumed per day had the lowest CHD mortality ratios. When all ex-
smokers were analyzed by the length of time since cessation (Figure
13), ex-smokers who had been abstinent for 20 or more years had a
CHD mortality ratio virtually identical to lifelong nonsmokers (1.00
versus 1.05). Friedman et al. (69) found that the benefits of quitting

124


TABLE 21.~ssation of smoking and CHD mortality ratios
      of current smokers versus ex-smokers, by
      number of cigarettes smoked daily, U.S.
      veterans study, M-year followup

No. cig/daily              Current smoker

Ex-smoker

Nonsmoker                  1.00               1.00
l-9                       1.24               1.02
lo-20                     1.56               1.14
2139                     1.76               1.31
40+                      1.94               1.30
AU smokers                  1.66               1.16

SOURCE: Begot and Murray (224).

A   8 C D E

FIGURE lb-Coronary heart disease mortality rates by
       number of years stopped smoking, U.S.
       veterans study, N-year followup

NOTE: A = Btopped b than 5 years: B = stopped 5-9 years; C = stopped 10-14 years; D = tipped 15-19
years; E = stopped 20 or more years.
SOURCE: Begot and Murray GW.

smoking could not be explained by differences in other risk factor
levels between continuing smokers and quitters.

Thus, cessation of cigarette smoking resulted in a reduction in the
risk of CHD in each of the mortality studies that have examined the
question. There appears to be some residual excess CHD risk in those
ex-smokers who smoked heavily for extended periods of time prior to

1%