MONDAY, Oct. 22 (HealthDay News) -- Women who gain weight any time after the age of 18 are more likely to develop breast cancer than women who maintain a stable weight, a new study suggests.

In other words, when it comes to breast cancer, there's no good time to gain weight as an adult.

"We found that weight gain throughout adulthood as well as weight gain at specific stages of life were associated with risk of breast cancer, compared with maintaining a stable weight," said study lead author Jiyoung Ahn, a fellow with the nutritional epidemiology branch at the National Cancer Institute's division of cancer epidemiology and genetics. "Specific stages include during early reproductive years, late reproductive years, and perimenopausal and postmenopausal years."

Ahn's findings included women who did not take menopausal hormone therapy, which has been linked to a heightened risk of breast cancer.

"This is just one more very important piece of evidence demonstrating the importance of weight gain to the development of breast cancer," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La.

The findings are published in the Oct. 22 issue of Archives of Internal Medicine.

Obesity has been shown to be a risk factor for breast cancer during the postmenopausal years. This is probably because estrogens, which fuel breast cancer growth, accumulate in fat tissue. It's been unclear, however, if the timing of weight gain might influence risk.

For the new study, the researchers analyzed data on almost 100,000 postmenopausal women who were participating in the National Institutes of Health-AARP Diet and Health Study.

At the beginning of the study, in 1996, the women reported their weight and body measurements at ages 18, 35 and 50. They were then classified, based on their body mass index, as underweight, normal weight, overweight or obese.

Among women who did not take menopausal hormone therapy, gaining weight in the early reproductive years (ages 18 to 35), the late reproductive years (ages 35 to 50), perimenopausal and postmenopausal years (age 50 to the present) and throughout adulthood (age 18 to the present) was associated with a heightened risk of developing breast cancer compared with women who maintained a stable weight.

Women who were at or below a normal weight at age 18 but were overweight or obese at ages 35 and 50 had 1.4 times the risk of developing breast cancer, compared with women who had maintained a normal weight. Women who subsequently lost weight had the same cancer risk as those who maintained a stable weight.

But isn't gaining weight a normal part of aging?

Experts increasingly are saying no.

"The issue was outside of the scope of this study, [but] limited data suggest that weight gain is not inevitable with age," Ahn said.

Brooks added: "In our society, most people gain weight [as they age] but that may not be what we should be doing. It's something you should be avoiding as you age. It's not something you should assume just because it's the societal norm."

More information

Visit the National Cancer Institute for more on breast cancer.

SOURCES: Jiyoung Ahn, Ph.D., fellow, nutritional epidemiology branch, division of cancer epidemiology and genetics, National Cancer Institute, Bethesda, Md.; Jay Brooks, chairman of hematology/oncology, Ochsner Health System, Baton Rouge, La.; Oct. 22, 2007, Archives of Internal Medicine

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