Weight gain in middle-age linked to breast cancer

According to new research women who gain weight throughout adulthood rather than maintaining a stable weight may have an increased risk for breast cancer.

Experts say obesity is known to be a risk factor for developing breast cancer after the menopause when estrogens may accumulate in fat tissue, potentially initiating or promoting the growth of cancerous cells in the breast.

For the study Dr. Jiyoung Ahn from the National Cancer Institute, Bethesda, and colleagues used data from the National Institutes of Health–AARP Diet and Health Study on 99,039 postmenopausal women.

At the start of the study in 1996, the women reported their current body measurements and weight, plus their weight at ages 18, 35 and 50; body mass index (BMI) was used to classify the women as underweight, normal weight, overweight or obese.

The researchers found that by 2000, 2,111 of the women who had not taken menopausal hormone therapy, had developed breast cancer.

Gaining weight in the early reproductive years (age 18 to 35), late reproductive years (age 35 to 50), perimenopausal and postmenopausal years (age 50 to the current age) and throughout adulthood (age 18 to the current age) were each associated with an increased risk of developing breast cancer compared with maintaining a stable weight during those periods.

The researchers found that women who were not obese or overweight at age 18 but were at ages 35 and 50 had 1.4 times the risk of developing breast cancer compared with women who maintained a normal weight.

Women who lost weight had the same breast cancer risk as those whose weight remained stable.

The study authors say because weight gain during adulthood mainly reflects the deposition of fat mass rather than lean body mass, weight gain potentially represents age-related metabolic change that may be important in breast cancer development.

They believe their findings reinforce public health recommendations for the maintenance of a healthy weight throughout adulthood as a means of breast cancer prevention.

Four out of five cases of breast cancer are diagnosed in women after the menopause and the risk rises with increasing age.

The hormone oestrogen can be supplied by fat cells as well as the ovaries and stimulates some breast cancers to grow.

The study is published in the current issue of Archives of Internal Medicine.