THE INFLUENCE OF CIGARETTE-SMOKING ON THE ASSOCIATION BETWEEN BODY-WEIGHT AND MORTALITY - THE FRAMINGHAM HEART-STUDY REVISITED

PURPOSE: To calculate for two measures of obesity, the Metropolitan Re lative Weight (MRW) and body mass index (BMI), the value at which mini mum mortality occurs. This was done to retest the hypothesis, in the F ramingham Heart Study data, that the association between obesity and m ortality can be obscured by an interaction between the measure of obes ity and smoking. In the original analysis of the Framingham data it wa s suggested that there was a U- or J-shaped relationship between MRW a nd death in smokers but a linear relationship in nonsmokers. The desig n and setting were those of the NHLBI Framingham Heart Study. METHODS: The 5209 members of the Framingham Heart Study underwent a baseline e xamination in 1948-1952 (Exam 1) and they were reexamined at approxima tely two-year intervals over a 30-year period. The study included both men (n = 2336) and women (n = 2873) in the age range of 28 to 62 year s. After excluding persons with missing baseline data, the analytic sa mple size was 5163. Additional analyses were conducted by deleting per sons with cardiovascular disease (CVD) at baseline (n = 135), the samp le used by the original paper by Garrison and colleagues, and persons who died within the first four years of follow-up (n = 62). The main o utcome measures consisted of thirty-year survival through Exam 16, app roximately in 1980, as influenced by MRW or BMI, age, and smoking stat us at baseline (Exam 1). RESULTS: We were able to show that the sample sizes of male nonsmokers were too small to test the hypothesis within age groups < 40 and 40-49 years. In men ages 50-62 there was a signif icant age adjusted quadratic relationship between BMI or MRW, and risk of death. The estimated BMI at the minimum risk of death for smokers (24.5) and nonsmokers (23.8) were not statistically different. Identic al results were found for MRW (minimum: smokers = 112.5, nonsmokers = 111.4). In men and women ages 28-62 there appeared to be a u- or j-sha ped relationship between the 30-year crude mortality rate and MRW. Aft er excluding persons with missing data, CVD at baseline, and persons w ho died within the first four years of follow-up, the age adjusted est imated BMI value at the minimum risk of death was nearly identical for men and women and for smokers and nonsmokers (Men: smokers = 22.8, no nsmokers = 22.8; Women: smokers = 22.9, nonsmokers = 23.3). Additional ly, the estimates of the minimum were always below the mean. Identical results were found without deleting persons with CVD at baseline and deaths in the first four years of follow-up. Identical results were fo und for MRW. CONCLUSIONS: Reanalysis of the Framingham Heart Study dat a does not support the hypothesis that there is an interaction between smoking and measures of obesity. Moreover, the estimated BMI or MRW a t the minimum risk of death was similar for men and women smokers and nonsmokers alike even after deleting prevalent cases of CVD and deaths within the first four years of follow-up. Published by Elsevier Scien ce Inc.