Cigarette smoking, relative weight, and menopause

To examine the interrelationships of cigarette smoking, relative weight, and the occurrence of natural menopause, the authors prospectively evaluated the experience of 66, 663 female US registered nurses who were premenopausal in 1976. Over a two-year period, 5004 women became post-menopausal. Current smokers were more likely than past or never smokers to develop menopause, although the effects of smoking diminished with age. The rate ratios of menopause for current smokers vs. never smokers (with 95% confidence limits) for women aged 30-39, 40-44, 45-49, and 50-55 years were 1.90 (1.10-3.28), 2.16 (1.73-2.69), 1.53 (1.41-1.67), and 1.20 (1.12-1.28). These rate ratios were not appreciably affected by adjustment for relative weight. Median ages at menopause were 52.4 for never smokers and 51.9, 51.0, 50.7, and 50.4 years for women who currently smoked 1-14, 15-24, 25-34, and 35 or more cigarettes per day. A crude linear relationship between relative weight and occurrence of menopause was observed. Comparing the leanest and heaviest quintiles, rate ratios for menopause among women aged 30-39, 40-44, 45-49, and 50-55 years were 1.42 (0.74-2.75), 1.26 (0.95-1.69), 1.25 (1.13-1.41) and 1.08 (0.99-1.19). The effect of relative weight was in part explained by the tendency of current smokers to weigh less than nonsmokers. After adjustment for current cigarette consumption a weak linear relationship between relative weight and menopause remained among women who smoked, although no such association was seen among nonsmokers

Relative weight and risk of breast cancer among premenopausal women

Although higher relative weight is generally considered to increase the risk of breast cancer, several case-control studies have suggested that the reverse may be true among premenopausal women. The association between Quetelot's index (a measure of relative weight calculated as weight/height) and the subsequent incidence of breast cancer was therefore examined during four years of follow-up among a cohort of 121,964 US women who were 30-55 years of age in 1976. In contrast to women who had experienced natural menopause or bilateral oophorectomy, the incidence of breast cancer among premenopausal women decreased with higher levels of relative weight Age-adjusted relative risks for increasing quintiles of Quetelef s index were 1.00, 0.90, 0.90, 0.73, and 0.66 (Mantel extension test for trend =-2.82, p = 0.005). This inverse association was not explained by known risk factors for breast cancer and was somewhat stronger when Quetelef s index was computed using reported weight at age 18 years. The excess incidence of breast cancer among lean premenopausal women, however, was limited to tumors that were less than 2.0 cm in diameter, were not associated with metastases to lymph nodes, and were well-differentiated. These findings suggest that the apparent excess risk of breast cancer among lean premenopausal women may result at least in part from easier, and thus earlier, diagnosis of less aggressive tumors