Obesity and Smoking: A Mortal Duo

BETHESDA, Md., Oct. 3 -- Obesity and smoking, when combined, add up to as much as a fivefold increase in the risk of early all-cause mortality.

Compared with normal weight, never-smokers, obese smokers, both men and women, face an estimated six- to 11-fold increase in risk of death from heart disease before age 65, reported epidemiologist D. Michael Freedman, Ph.D., of the National Cancer Institute, and colleagues, in the November issue of the American Journal of Preventive Medicine.

For women, the increased risk was more dramatic than for men, Obese women smokers younger than 65 were 10.64 times more likely to die of circulatory disease than same-age, normal weight women who never smoked. But when obese women stopped smoking the relative risk dropped to 3.81.

For obese men younger than 65 the relative risk was 6.01 compared with age-matched normal weight non-smoking men. As with women, the risk declined for obese men who stopped smoking but the decline was not as precipitous, with a relative risk declining from a sixfold increase to a fourfold rise.

Dr. Freedman and colleagues assessed mortality risk in 64,120 women and 18,760 men who participated in the U.S. Radiologic Technologies Study, an ongoing collaboration of the National Cancer Institute, the University of Minnesota, and the American Registry of Radiologic Technologists.

All participants completed self-administered baseline questionnaires from 1983 to 1989 that included data on age, gender, height, weight, smoking history and medical history.

The participants were categorized by body mass index into five groups: underweight (BMI less than 18.5), normal (18.5 to 24.9), overweight (25.0 to 29.9), moderately obese (30 to 34.9) and very obese (BMI of 35 and higher).

The data were also analyzed by gender and age-younger than 65 or older than 65.

The patients were followed form the date of the questionnaire through death or 2002, which ever occurred first.

Among the findings:

• Regardless of age or sex, the combination of obesity and smoking increased all cause mortality.
• Women smokers younger than 65 who were extremely obese had a 5.2 relative risk for all cause mortality compared with normal weight women who didn't smoke. For extremely obese men younger than 65 who smoked the relative risk was 4.19.
• The relative risk of all cause mortality decreased to 1.88 for extremely obese women younger than 65 who stopped smoking and to 2.05 for extremely obese men younger than 65 who stopped smoking.
• The relative risk of dying from cancer was 2.45 for obese women smokers younger than 65, and 1.7 for those 65 or older, versus 2.77 and 3.05 in obese male smokers younger than 65 and 65 or older, respectively.

The study was limited by its reliance on self-reported height and weight, because it is probable that heavy individuals under-reported their weight and as a result BMI may have been underestimated, the authors wrote. Other limits included the lack of data on physical activity or abdominal obesity.

The authors concluded that additional studies are needed to clarity the "relationship among excess weight, smoking, and morality, and particularly, to examine whether combined risk is especially elevated in younger women."