Women Who Gain Significant Weight in Adulthood Increase Risk of Postmenopausal Breast Cancer, UB Study Finds

BUFFALO, N.Y -- If new mothers need a reason to shed pounds gained during pregnancy other than to fit into their pre-pregnancy clothes, a new study from the University at Buffalo provides it.

UB epidemiologists have found a strong association between weight gain and risk of postmenopausal breast cancer for women who put on the most pounds between their first pregnancy and menopause, compared to those who gained the least.

Women who gained in the neighborhood of 60 pounds during the period from first pregnancy to menopause were twice as likely to develop breast cancer compared with those whose gain was about 20 pounds. And the longer a woman remained at a higher weight, the greater the breast-cancer risk.

There was no association between lifetime weight gain and breast-cancer risk in premenopausal women, between weight or weight changes at the age of 20 and breast-cancer risk, or body shape at menarche, results showed.

The study findings were presented today (June 15) at the Society for Epidemiological Research meeting in Salt Lake City. Daikwon Han, Ph.D., research assistant professor in the Department of Social and Preventive Medicine, UB School of Public Health and Health Professions, is principal researcher.

"There is quite consistent data showing an association between increased risk of postmenopausal breast cancer and increased body mass index," said Han. "And although previous studies suggested that timing of weight change through a women's reproductive life, not simply total weight change, may be related to breast cancer risk, this association has not been clearly identified.

"Our findings provide evidence that weight gained at certain reproductive time points may be an important risk factor, especially weight gained between first pregnancy and menopause," said Han.

The study involved 1,170 women who had had breast cancer and 2,116 women selected randomly and matched to cases by age and race. Participants recorded their weight at every 10 years of life from age 20 until the present. Using weight at age 20 to represent weight in early life, Han created new variables on weight (and weight changes) to represent certain time points, such as first pregnancy and menopause. Researchers also conducted extensive interviews to determine overall individual cancer risk factors.

Results showed that postmenopausal women in the highest quartile of weight gain -- 27 kilograms (kg) or 59.5 pounds since age 20 -- were at twice the risk of developing breast cancer compared to women in the lowest quartile who had gained 9 kg (21.7 pounds) or less over a lifetime. The longer a woman remained at a higher weight, the greater the risk of postmenopausal breast cancer, findings showed. In addition, researchers found that hormone replacement therapy appeared to weaken the association between postmenopausal breast cancer and weight gain.

"This study suggests that there may be important time points in relation to weight change and breast-cancer risk, especially among postmenopausal women," said Han.

Additional researchers on the study from the UB Department of Social and Preventive Medicine, School of Public Health and Health Professions, were Maurizio Trevisan, M.D., professor and interim dean, Paola Muti, M.D., Ph.D., Jing Nie, Dominica Vito, and Jo Freudenheim, department chair. Stephen Edge, M.D., from Roswell Park Cancer Institute, was also a contributing researcher.

The study was funded by grants from the National Institutes of Health and the U.S. Army Office of Medical Research.

The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.