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Circulation. 1997;96:1438-1444

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(Circulation. 1997;96:1438-1444.)
© 1997 American Heart Association, Inc.


Articles

Cigarette Smoking, Weight Gain, and Coronary Mortality

Results From the Chicago Western Electric Study

Janet E. Fulton, PhD; ; Richard B. Shekelle, PhD

From The University of Texas–Houston, Health Science Center, School of Public Health.

Correspondence to Janet E. Fulton, PhD, Centers for Disease Control and Prevention, Division of Nutrition and Physical Activity, 4770 Buford Highway Northeast, Mailstop K46, Atlanta, GA 30341-3724.


*    Abstract
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*Abstract
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Background Prospective studies of overweight and coronary heart disease (CHD) have presented inconsistent findings. Previous inconsistencies may be explained by the modifying effect of cigarette smoking on the association between weight gain and coronary mortality.

Methods and Results We prospectively studied 1531 men 40 to 59 years of age who were employed at the Hawthorne Works of the Western Electric Company in Chicago, Ill. Information collected at the initial examination in 1958 included recalled weight at age 20, present weight, height, smoking status, and other CHD risk factors. Vital status was known for all men on the 25th anniversary: 257 CHD deaths occurred over 31 644 person-years of experience. Cox regression analysis was used to investigate risk of coronary mortality associated with change in body mass index ({Delta}BMI) and its modification by smoking status after adjustment for age, major organ system disease, family history of CHD, and BMI at age 20. Adjustment was not performed for blood pressure or serum total cholesterol because these are intervening variables. {Delta}BMI was positively associated with risk of coronary mortality in never-smokers but not in current-smokers (P for interaction=.088). For never-smokers with {Delta}BMI classified as stable, low gain, moderate gain, or high gain, adjusted relative risks of coronary mortality were 1.00, 1.75, 1.75, and 3.07, respectively (P for trend=.010). For current-smokers, the respective adjusted relative risks were 1.00, 0.78, 1.05, and 1.03 (P for trend=.344).

Conclusions These results support the hypothesis that cigarette smoking modifies the association between weight gain and coronary mortality. Future investigations of weight gain and coronary mortality should account for the modifying effect of cigarette smoking.


Key Words: obesity • epidemiology • cardiovascular diseases • exercise


*    Introduction
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Overweight is a major and increasing problem in the United States. The prevalence of overweight has increased from 25% in 1980 to 33% in 1991 such that >34 million Americans are currently considered to be overweight.1 The propensity toward overweight in this country is coupled with the dilemma that weight usually increases while physical activity decreases with age.2 3 It is therefore likely that adult overweight will continue to be an important public health challenge for years to come.

Overweight is clearly associated with the development of coronary heart disease (CHD) risk factors.4 However, prospective studies of overweight and coronary heart disease have reported inconsistent findings.5 6 To date, investigators have reported positive,7 8 9 10 negative,11 and null12 13 14 associations between overweight and weight gain and risk of CHD. Obesity at the extremes appears to increase the risk of all-cause mortality,6 although the magnitude of risk associated with intermediate levels of overweight or weight gain has not been clearly defined. Clarification of previous inconsistent findings is essential to accurately estimate the magnitude of the effect of weight gain on risk of CHD.

The great majority of persons in the United States gain weight during their young adulthood,1 15 but cigarette smokers may gain less weight than nonsmokers due to the metabolic effect of smoking on weight.16 17 18 Effects of nicotine on the resting metabolic rate19 20 or the sympathetic nervous system21 22 23 may account for an increase in energy expenditure and/or a decrease in energy storage, which may explain why smokers tend to weigh less than their nonsmoking counterparts and gain weight on cessation of smoking. Moreover, cigarette smokers may remain lean during their adult years not due to a physically active lifestyle or prudent diet but rather due to their cigarette smoking behavior, making it difficult to assess the true effect of weight gain on coronary disease in cigarette smokers. Examination of the association between weight gain and CHD mortality as being modified by cigarette smoking may help to clarify previous inconsistent findings between overweight and CHD.5 6 We hypothesized that cigarette smoking modifies the association between gain in weight during young adulthood and risk of 25-year CHD mortality in a cohort of 1531 middle-aged, employed men. Specifically, weight gain during young adulthood will be positively associated with 25-year risk of CHD mortality in nonsmokers, but the association will be smaller or absent entirely in cigarette smokers. This report presents a test of this hypothesis.


*    Methods
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*Methods
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Participant Selection
Participants in the Western Electric Study were selected in 1957 from the population of 5397 men whose records indicated that they were 40 to 55 years of age and had been employed for >=2 years at the Hawthorne Works of the Western Electric Company in the Chicago, Ill, area. Of 3102 randomly selected men, 2080 (67.1%) agreed to participate. Another 27 men served as a pilot group, bringing to 2107 the total number examined from October 1957 through December 1958. Two thirds of the men were first-generation or second-generation Americans, predominantly of German, Polish, or Bohemian ancestry. The remainder were mostly descendants of earlier emigrants from the British Isles. The men worked at various occupations associated with the manufacture of telephones and related products. Selection, examination, and follow-up procedures have been described elsewhere.24

Of the 2107 men initially examined, 62 did not return for the second examination in 1959 and were excluded from the present study because data from both examinations were required. An additional 74 men (3.6% of 2045) were excluded due to evidence of CHD at either the first or second examination. Of the remaining 1971 men who attended both examinations and did not have evidence of CHD, others were excluded due to missing data on weight (n=36) and cigarette smoking status (n=1). Men reporting being a former cigarette smoker at the baseline examination were excluded from the present analysis (n=242). Individuals who had a decrease in body mass index (BMI) (loss in BMI >0.74 kg/m2) (n=161) were excluded because gain in BMI was the exposure variable of interest for this investigation. Thus, the population at risk for coronary mortality for this investigation comprised 1531 employed men.

Data Collection
The initial examination included a detailed family and medical history with recall of weight at ages 20, 25, 30, 35, and 40; physical examination; and measurement of height, weight, and skinfold thickness (measured at the tip of the scapula and at the triceps). Body mass index (ie, Quetelet's index) (kg/m2) was used as an estimate of body fatness due to its correlation with sum of skinfolds and body density and lack of correlation with height.25 Systolic and diastolic blood pressures were taken at the beginning of each physical examination with the participant seated. Serum total cholesterol was measured according to the method of Abell et al.26 History of using tobacco and current use of tobacco (cigarettes, pipes, cigars, and other) was routinely asked each year as part of the medical history. Participants self-reported their cigarette smoking status (never, former, or current cigarette smoker) and past use of cigarettes (duration of use, amount smoked most of adult life, and, for former users, the period of time since the last use) at the baseline examination.

Major organ system disease was considered present at the initial examination when any one or more of the following conditions were present: history of diabetes mellitus, 2+ urine sugar, cardiomegaly or other clinically significant finding on chest radiograph, hypertensive retinopathy, or a major ECG abnormality. Family history of cardiovascular disease was self-reported at the baseline examination and coded positive for cardiovascular diseases if a parent had died from such causes before age 60 or a sibling had died from such causes at any age past childhood.

Follow-up
Men who continued to participate in the study were reexamined annually up to 1969. After 1969, vital status was determined periodically by mailed questionnaire and telephone interview through the 25th anniversary of the initial examination; at that time vital status was known for all 2107 men. Underlying cause of death and up to four additional causes on the death certificate were coded according to the Eighth Revision of the International Classification of Diseases adapted for use in the United States.27 Codes 410–412 were coded as CHD deaths.

Analysis
The increase in body fatness from age 20 until baseline was the primary exposure variable of interest for this investigation as measured by the change in BMI from age 20 to baseline examination (ie, during young adulthood and middle age). To reduce the effects of intraindividual variation, participants were characterized at baseline by mean values of measurements made at the first and second examinations in 1958 and 1959 with respect to current BMI, cigarettes smoked per day, systolic blood pressure, and serum total cholesterol. BMI at age 20 (kg/m2) was calculated as recalled weight at age 20 divided by measured height in 1958. BMI at baseline was calculated as the mean of measured weight at the baseline examination in 1958/1959 divided by measured height in 1958. Change in BMI ({Delta}BMI) during young adulthood was calculated by subtracting BMI at age 20 from BMI at baseline. Cigarette smokers were classified as never-smokers (reported never smoking cigarettes at baseline) or current-smokers (reported currently smoking cigarettes at baseline). Subsequent analyses were stratified by never or current cigarette smoking. Age at baseline was determined as the date of the second examination minus the date of birth. Time at risk for coronary mortality was calculated as the number of days from the date of the second examination to the date of death or the 25th anniversary, whichever came first.

Proportional hazards regression analysis was used to investigate the association between {Delta}BMI and 25-year coronary mortality separately for never-smokers and current-smokers to test the hypothesis that cigarette smoking modifies the association between {Delta}BMI and coronary mortality. Relative risks (RRs) of coronary mortality were adjusted for age, family history of CHD, major organ system disease, BMI at age 20, and number of cigarettes smoked per day. Relative risks of coronary mortality were not adjusted in the primary analysis for systolic blood pressure or total serum cholesterol because these were believed to be intervening variables. The cross-product of cigarette smoking and {Delta}BMI was calculated and added to the proportional hazards regression model to evaluate the statistical probability of effect modification.


*    Results
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*Results
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The prevalence of never-smoking and currently smoking cigarettes at the baseline examination in 1958 was 32.4% (n=575) and 53.9% (n=956), respectively. Former cigarette smokers constituted 13.7% (n=242) of the cohort and were excluded from the present analyses.

Table 1Down shows the participant characteristics by cigarette smoking status at the baseline examination. Never-smokers and current-smokers were of similar age (49 years) and height (175 cm) at baseline. As expected, mean weight of current-smokers was significantly lower than that of never-smokers (77.8 and 80.5 kg, respectively). Mean BMI at age 20 was the same between never-smokers and current-smokers (22.2 kg/m2), although mean BMI at baseline (middle-age) was significantly lower for current-smokers than never-smokers (25.5 and 26.5 kg/m2, respectively). Never-smokers gained significantly more BMI than current-smokers over the course of their young adulthood (4.3 and 3.3 kg/m2, respectively).


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Table 1. Participant Characteristics by Cigarette Smoking Status at Baseline Examination for 1531 Employed Men Age 40 to 59 Years: Western Electric Study, 1958–1959

{Delta}BMI was categorized as stable, low gain, moderate gain, or high gain. Stable was defined as losing or gaining no more than 0.74 kg/m2 (ie, stable=±0.74 kg/m2), which is equal to 5 lb divided by (1.75 m)2, where 1.75 m is the mean height of the cohort. The low-, moderate-, and high-gain categories were tertiles of gain in BMI calculated after excluding the stable category. Low-, moderate-, and high-gain categories corresponded to changes in BMI of >0.74 and <= 2.90, >2.90 and <= 4.90, and >4.90 kg/m2, respectively. The median change in BMI among the stable, low-gain, moderate-gain, and high-gain categories was 0.05, 1.90, 3.85, and 6.40 kg/m2, respectively.

Fig 1Down shows the prevalence of each category of {Delta}BMI by cigarette smoking status. Never-smokers compared with current-smokers had lower prevalence of stability in BMI (7% versus 15%, respectively). Conversely, the prevalence of high gain in BMI was somewhat higher in never-smokers than current-smokers (37% versus 24%, respectively). Prevalence of category of {Delta}BMI was significantly different between never-smokers and current-smokers ({chi}2 [3]=47.8, P<.001).



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Figure 1. Prevalence of categories of change in body mass index (BMI) by cigarette smoking status among 1531 employed men, Western Electric Study, 1958 to 1983. Change in BMI equals average BMI in 1958 and 1959 minus BMI at age 20, categorized as stable (±0.74 kg/m2), low gain (>0.74 to <=2.90 kg/m2), moderate gain (>2.90 to <=4.90 kg/m2), and high gain (>4.90 kg/m2). Prevalence of category of change in BMI was significantly different between never-smokers and current-smokers, {chi}2 (3)=47.8, P<.001.

Figs 2Down and 3Down show the mean BMI at ages 20, 25, 30, 35, and 40 by {Delta}BMI category for never-smokers and current-smokers, respectively. Gain in BMI occurred linearly from age 20 to 40 among the low-, moderate-, and high-gain groups for never-smokers and current-smokers alike. The stable group remained BMI stable from age 20 to 40. Among never-smokers, change in BMI from age 20 to 40 among the stable and low-, moderate-, and high-gain groups ranged from 23.6 to 24.2, 23.0 to 25.4, 22.2 to 25.8, and 21.3 to 27.3, respectively. Similarly, among current-smokers, corresponding changes in BMI from age 20 to 40 were 23.1 to 23.9, 22.6 to 24.7, 22.0 to 25.7, and 21.3 to 26.9, respectively. Similar patterns of increase in BMI were observed among never-smokers and current-smokers. Gain in BMI was inversely related to BMI at age 20 and thus BMI at age 20 was an important variable to control for in the multivariate analysis of {Delta}BMI and CHD mortality.



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Figure 2. Mean body mass index (BMI) (kg/m2) at ages 20, 25, 30, 35, and 40 by category of change in BMI among never-smokers. Change in BMI equals average BMI in 1958 and 1959 minus BMI at age 20, categorized as stable (±0.74 kg/m2), low gain (>0.74 to <=2.90 kg/m2), moderate gain (>2.90 to <=4.90 kg/m2), and high gain (>4.90 kg/m2).



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Figure 3. Mean body mass index (BMI) (kg/m2) at ages 20, 25, 30, 35, and 40 by category of change in BMI among current-smokers. Change in BMI equals average BMI in 1958 and 1959 minus BMI at age 20, categorized as stable (±0.74 kg/m2), low gain (>0.74 to <=2.90 kg/m2), moderate gain (>2.90 to <=4.90 kg/m2), and high gain (>4.90 kg/m2).

Table 2Down shows the mean values of age, systolic blood pressure, and serum total cholesterol by {Delta}BMI category and cigarette smoking status. Gain in BMI was associated with higher mean systolic blood pressures at baseline (P<.001), but cigarette smoking was not (P=.435). Gain in BMI (P=.052) and cigarette smoking (P<.001) were associated with higher mean serum total cholesterol values at baseline.


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Table 2. Age and CHD Risk Factors by {Delta}BMI Category and Cigarette Smoking Status Measured at Baseline Examination Among 1531 Employed Men: Western Electric Study, 1958–1983

The association between {Delta}BMI and risk of CHD mortality separately for never-smokers and current-smokers was examined as shown in Table 3Down. For never-smokers in {Delta}BMI categories of stable, low gain, moderate gain, and high gain, corresponding adjusted RRs of CHD mortality were 1.00, 1.75, 1.75, and 3.07 (P for trend=.010).


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Table 3. The 25-Year Risk of Coronary Mortality by Strata of {Delta}BMI and Cigarette Smoking Status Among 1531 Employed Men: Western Electric Study, 1958–1983

To decrease the effect of variability within each category of {Delta}BMI, the median value of each {Delta}BMI category was used to assess the effect of {Delta}BMI as a continuous variable. Among never-smokers, the adjusted relative risk of CHD mortality by {Delta}BMI was 1.16 (95% confidence interval, 1.04 to 1.30), indicating for every one unit change in BMI during young adulthood there was a corresponding 16% increase in the 25-year risk of CHD mortality.

Among current-smokers in {Delta}BMI categories of stable, low gain, moderate gain, and high gain, corresponding adjusted relative risks of CHD were 1.00, 0.78, 1.05, and 1.03 (P for trend=.344). Among current-smokers, the adjusted relative risk of CHD mortality for {Delta}BMI as a continuous measure was 1.02 (95% confidence interval, 0.96 to 1.09). Thus, among current-smokers, there was no association between {Delta}BMI and CHD mortality. Within {Delta}BMI categories, crude rates of CHD mortality in current-smokers were greater than crude CHD mortality rates in never-smokers.

Effect modification by cigarette smoking was evaluated by creating an interaction term between median values of change in BMI and never or currently smoking cigarettes (0, never smoking; 1, current smoking). The interaction term was added to the proportional hazards regression model containing age, major organ system disease, family history of CHD, BMI recalled at age 20, number of cigarettes smoked per day at baseline, median change in {Delta}BMI, and never- or current-smoking cigarettes. The adjusted RR of CHD associated with the interaction term was 0.90 (P=.088).

Alternate explanations for the results were considered and addressed in post hoc analyses. Misclassification of exposure was evaluated by examining the risk of CHD in several alternative ways. Among never-smokers, using alternative groupings of {Delta}BMI yielded RRs ranging from 1.0 to 1.8 (P for trend=.027). Inclusion of individuals with preexisting disease at the baseline examination was addressed by excluding deaths occurring during the first 5 years of follow-up and yielded RRs ranging from 1.7 to 2.8 (P for trend=.025). Exclusion of individuals with diabetes or major organ system disease or a former alcohol drinker yielded RRs ranging from 1.4 to 3.0 (P for trend=.022), and exclusion of persons with unusually low or high BMI at age 20 (<18 or >28 kg/m2) yielded RRs ranging from 1.7 to 3.1 (P for trend=.008). Controlling for the intervening variables, systolic blood pressure, and serum total cholesterol, low-, moderate-, and high-gain RRs were 2.0, 1.7, and 2.9 (P for trend=.035). Furthermore, when controlling for baseline triceps and subscapular skinfold measures, low-, moderate-, and high-gain RRs were 1.8, 1.7, and 3.0 (P for trend=.015). Confounding by alcohol drinking was explored in preliminary analyses and yielded corresponding RRs of 1.8, 1.8, and 3.1 (P for trend=.011). No trend was observed for current smokers in any of these post hoc analyses.


*    Discussion
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up arrowResults
*Discussion
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These results support the hypothesis that cigarette smoking modifies the association between change in {Delta}BMI during young adulthood and risk of 25-year coronary mortality. Among never-smokers, men who gained BMI during their young adulthood had 1.8 to 3.1 times the risk of 25-year CHD mortality compared with men with stable BMI. By contrast, among current-smokers, there was no association between change in BMI and 25-year coronary mortality. Furthermore, stable BMI was more common and moderate or high gain in BMI was less common in current-smokers than in never-smokers. These results support the idea that there is a blunting effect on the physiological process of weight gain among cigarette smokers.17 18 28 This biologic phenomenon may cause the association between weight gain and CHD death to be obscured in individuals who are current cigarette smokers. Thus, cigarette smokers may remain lean through their young adulthood, not due to a physically active lifestyle or a prudent diet but instead due to their smoking behavior, making it difficult to estimate the true risk of CHD death associated with weight gain in populations in whom cigarette smoking is prevalent. Failure to detect a positive association between weight or weight gain and CHD in previous investigations may have been due to inadequate examination of cigarette smoking.

Are These Results Consistent With Other Studies?
Many researchers have investigated the association between obesity and CHD, but only recently have investigators studied the extent to which gain in weight or BMI was associated with CHD or all-cause mortality. In Harvard alumni who reported their weight in 1962 or 1966 and again in 1977, increased risk of CHD mortality (RR, 1.28 to 2.01) was observed in men who gained weight compared with men with stable weight.7 The authors did not statistically test for effect modification by cigarette smoking, although they did point out that a U-shaped relation between weight change and all-cause mortality was demonstrated among nonsmokers only. Harvard alumni may not be typical of many US men because 17% currently smoked cigarettes in 1977 and only 12% gained >5 kg from 1962 to 1977. In comparison, 54% of men in the Western Electric study were current smokers, and 76% gained >5 kg from age 20 until the baseline examination in 1958.

Rimm and colleagues9 evaluated weight gain since age 21 and risk of incident CHD among 29 122 men participating in the Health Professionals Follow-Up Study. Results showed a positive association between weight gain and risk of 3-year incident CHD such that men gaining >=19 kg were 2.1 times more likely to develop CHD than were men with stable weight (±2 kg). In a similar study with women, Willett and colleagues10 investigated the risk of CHD associated with weight gain since age 18 among 115 818 female nurses in the Nurses' Health Study. Women gaining >=20 kg were 2.7 times more likely to develop CHD than were women with a stable weight (±4.9 kg). These results are in agreement with those of the present study as these populations had many fewer current cigarette smokers than the present study population. Thus, cigarette smoking in these studies could not substantially distort the relation between gain in weight and risk of subsequent CHD.

Could Misclassification of Exposure Have Biased the Result?
{Delta}BMI was calculated based on recalled weight at age 20 and measured weight and height at the baseline examination in 1958/1959. We did not directly validate recalled weight at age 20 in this study population, although previous investigators have demonstrated strong correlations between recalled weight at age 2529 and age 1810 with records of measured weight (r=.80 and .87, respectively). BMI is uncorrelated with height (r=.00 to .254) and highly correlated with the sum of skinfolds (r=.61 to .85) and body density from hydrostatic weighing (r=-.66 to -.85), indicating that it is a good proxy for body fatness.25 Choice of cut points of strata of {Delta}BMI is not a reasonable explanation for the present result in light of secondary analyses indicating the pattern of association between {Delta}BMI and CHD death was similar when the data were analyzed using alternative groupings of {Delta}BMI.

Cigarette smoking behavior was believed to be concurrent with gain in BMI from age 20 to baseline. However, cigarette smoking status was collected at the baseline examination in 1958. Misclassification of cigarette smoking status may have occurred during age 20 to baseline, although the mean duration of cigarette smoking among current smokers was 28 years (SD, 6 years), indicating that most current smokers started to smoke cigarettes in their early 20s.

Could Increased CHD Mortality Associated With {Delta}BMI Be the Result of Including Individuals With Subclinical or Preexisting Disease at Baseline Examination? Could Weight Loss Due to Premorbid Conditions Be a Determinant of CHD Mortality?
These alternative explanations are implausible for several reasons. First, when deaths occurring during the first 5 years of follow-up were excluded, the pattern of association between {Delta}BMI and CHD death did not change appreciably. Second, when individuals with diabetes or major organ system disease or a former alcohol drinker were excluded, the results were minimally affected. Third, exclusion of persons with unusually low or high BMI at age 20 (<18 or >28 kg/m2) did not appreciably change the results, indicating that individuals with preclinical disease were likely not influencing the association between {Delta}BMI and CHD death in never-smokers.

Could Misclassification of CHD Mortality or Chance Have Influenced the Result?
This is highly unlikely because complete 25-year follow-up was obtained for every member of the cohort. On the 25th anniversary of the first examination, the vital status of all 2107 participants was determined. All death certificates were obtained and coded,27 without knowledge of other information about participants. Misclassification of CHD mortality was unlikely, although the inability to examine acute myocardial infarction as a CHD end point is a limitation of the study. Chance could have been an alternate explanation for the result as the confidence intervals around the RRs included unity, although examination of a linear trend in the RRs is unaffected by the width of the confidence intervals around the risks.

We hypothesized that blood pressure and serum total cholesterol were intermediate in the causal pathway between gain in BMI and CHD death. Therefore, we did not control for their effect in the primary analysis. In a secondary analysis, however, the relative risks of CHD death by {Delta}BMI strata among never-smokers were slightly lower when the intervening variables, systolic blood pressure and serum total cholesterol, were included in the analysis. We hypothesized that the association between {Delta}BMI and CHD death would diminish as at least part of the variance in CHD death could be explained through the influence of {Delta}BMI on blood pressure and total cholesterol.30 This result may suggest that gain in BMI is directly influencing CHD mortality not through its influence on blood pressure or cholesterol but via a different mechanism. Or, perhaps more likely, gain in BMI may be a surrogate for another factor (eg, body fat patterning) that is associated with the excess CHD mortality seen among individuals who gain large amounts of BMI during young adulthood.31 Body fat patterning or central adiposity may work through other biological pathways to influence CHD mortality that are only moderately associated with blood pressure and total cholesterol and not intermediate in the causal chain. However, when analyses were controlled for triceps and subscapular skinfold measures at baseline, the RRs of CHD mortality changed only slightly. Furthermore, a chronic increase in body fat may affect other biological pathways leading to CHD mortality. Recently proposed mechanisms such as lipoprotein(a) and apolipoprotein E or the well-established CHD risk factors, HDL and LDL cholesterol may be the factors most influenced by weight gain32 33 that ultimately lead to CHD. These particular lipoprotein subcomponents were not obtained in the Western Electric cohort but may explain why total cholesterol does not appear to be an intermediary variable in this analysis.

The increased mechanization of modern societies as a result of advances in technology to encourage sedentary lifestyles combined with abundant and palatable food sources have resulted in a large proportion of the population being classified as obese or overweight.34 Physical inactivity is an independent risk factor for CHD,35 and evidence is accumulating to suggest that physical inactivity is the most important cause of weight gain in adulthood.36 Weight gain may be due to decreased energy expenditure related to physical inactivity rather than increased energy intake.36 37 38 39 It is proposed that prevention, or a decrease in the rate of progression, of gain in weight during adulthood may be best achieved through promotion of regular, moderately intense physical activity.35 40 41 42 Adult weight gain may be associated with risk of CHD largely as a marker for chronic physical inactivity that can be detected accurately only among nonsmokers due to the interfering effect of cigarette smoking on weight and weight gain. Thus, smokers may remain lean due to their cigarette smoking behavior and not from maintaining a physically active lifestyle or eating a prudent diet.

In conclusion, in this prospective cohort study, we demonstrated that cigarette smoking modifies the association between gain in BMI during young adulthood and 25-year CHD mortality. The evidence presented here may therefore aid in clarifying previous inconsistent results concerning obesity and CHD. Future investigations of weight gain and CHD mortality should account for the modifying effect of cigarette smoking.


*    Acknowledgments
 
Dr Fulton is indebted to Drs Darwin R. Labarthe, Ralph F. Frankowski, and James M. Pivarnik for their assistance and contributions to her doctoral dissertation research.


*    Footnotes
 
Guest editor was Henry H. Blackburn, MD, University of Minnesota.

Received February 10, 1997; revision received March 25, 1997; accepted April 9, 1997.


*    References
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*References
 
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