BOSTON -- Women who gain weight as adults and after menopause are at an increased risk for breast cancer, but the reverse is also true, researchers here reported.
BOSTON, July 11 -- Women who gain weight as adults and after menopause are at an increased risk for breast cancer, but the reverse is also true, according to researchers here.
Among nearly 50,000 women who were followed for up to 24 years, about 15% of breast cancers could be attributed to weight gain of more than 2.0 kg (4.4 lbs) since age 18, wrote A. Heather Eliassen, Sc.D., of Brigham and Women's Hospital.
Conversely, women who lost weight after menopause had a 57% lower relative risk (P=0.01) for breast cancer than women who maintained or gained weight, Dr. Eliassen and colleagues at Harvard Medical School and the Harvard School of Public Health, wrote in the July 12 issue of Journal of the American Medical Association.
"An important finding from this study is that weight loss may reduce breast cancer risk, even if weight is not lost until after menopause," they added.
"Although these data suggest that it is never too late to lose weight to decrease risk, given the difficulty in losing weight, the emphasis must also remain on weight maintenance throughout adult life," they added.
The investigators arrived at their conclusions by way of a prospective study of women who took part in the landmark Nurses' Health Study. A total of 87,143 women ages 30 to 55 and free of cancer were followed for up to 26 years to assess their weight change since the age of 18 years. The current study expands on a previous analysis of weight change in this group, published in JAMA in 1997.
The authors also looked at weight change since menopause among 49,514 of the women who were followed for up to 24 years. The main study outcome was the rate of invasive breast cancer.
In all, there were 4,393 incident cases of invasive breast cancer. Women who gained 25 kg (55 lbs) or more since they were in their late teens had a 45% increase in risk for breast cancer (relative risk, 1.45; 95% confidence interval, 1.27-1.66; P<0.001 for trend), compared with women who maintained weight over their adult lives.
Among women who had never taken postmenopausal hormones, the risk for weight gain after menopause was two-fold compared with weight maintenance (relative risk 1.98; 95% CI, 1.55-2.53).
Among those women who gained 10.0 kg (22 lbs) or more since menopause, the relative risk for breast cancer was 1.18 (95% CI, 1.03-1.35; P =0.002 for trend) compared with women who had no significant weight change.
Weight loss after menopause, in contrast, appeared to be protective against breast cancer.
"Women who had never used postmenopausal hormones, lost 10.0 kg or more since menopause, and kept the weight off were at a lower risk than those who maintained weight," the authors wrote.
The relative risk for postmenopausal weight loss vs. maintenance was (0.43; 95% CI, 0.21-0.86; P=0.01 for weight loss trend).
"Overall, 15.0% (95% CI, 12.8%- 17.4%) of breast cancer cases in this population may be attributable to weight gain of 2.0 kg or more since age 18 years and 4.4% (95% CI, 3.6%-5.5%) attributable to weight gain of 2.0 kg or more since menopause," the authors wrote. "Among those who did not use postmenopausal hormones, the population attributable risks are 24.2% (95% CI, 19.8%-29.1%) for a weight gain since age 18 years and 7.6% (95% CI, 5.9%- 9.7%) for weight gain since menopause."
The authors said that the finding that the interaction between postmenopausal exogenous hormones, weight gain, and breast cancer may be due to the fact that after the age of menopause, adipose tissue is the primary source of estrogens, from aromatization of adrenal androgens.
"This interaction between weight change and postmenopausal hormone use is likely because exogenous hormones increase circulating estrogen levels among all women, regardless of adiposity, and thus obscure the gradient due to adipose tissue alone. Thus, an association between weight change and breast cancer is most clearly observed in women who have never used postmenopausal hormones," they wrote.
The authors acknowledged the difficulty of weight loss, especially after menopause, and recommended an emphasis on weight maintenance as a more realistic means of reducing breast cancer risk in both pre- and postmenopausal women.
They noted several limitations of the study including recalled weight at age 18 years and the fact that relatively few women lose weight, particularly after menopause. They felt that more follow-up is needed to confirm the findings and characterize the benefits more precisely.