Weight Gain Ups Breast Cancer Risk

Oct. 22, 2007 -- Throughout adulthood, especially in the years before and during menopause, weight gain raises a woman's risk of breast cancer.

It's been known for years that obese and overweight women have a higher risk of breast cancer than do women who stay fit and keep their weight down. Now, a study from the National Cancer Institute (NCI) and the AARP shows that weight gain throughout a woman's adult life affects her breast cancer risk.

"We found that weight gain throughout adulthood -- as well as weight gain at specific stages of life -- were associated with risk of breast cancer," NCI researcher Jiyoung Ahn, PhD, tells WebMD.

Ahn and colleagues analyzed data on nearly 100,000 women aged 50-71 collected via an NCI questionnaire sent out to AARP members. Cancer data came from cancer registries.

Compared with women who maintained a stable weight since age 18, the study showed that:

• Women who gained more than 66 pounds from age 18 to 35 had a 65% higher risk of breast cancer.
• Women who gained more than 66 pounds from age 35 to 50 had a 223% higher risk of breast cancer.
• Women who gained 44 to 66 pounds from age 35 to 50 had a 56% higher risk of breast cancer.
• Women who gained 22 to 44 pounds from age 35 to 50 had a 31% higher risk of breast cancer.
• Women who gained more than 66 pounds from age 50 to their current age had a 94% higher risk of breast cancer.
• Women who gained 44 to 66 pounds from age 50 to their current age had a 45% higher risk of breast cancer.
• Women who gained 22 to 44 pounds from age 50 to their current age had a 46% higher risk of breast cancer.
• Women who gained 4.4 to 22 pounds from age 50 to their current age had a 32% higher risk of breast cancer.

Eugenia Calle, PhD, managing director of analytic epidemiology at the American Cancer Society, says the findings show that the timing of weight gain has a lot to do with breast cancer risk.

"If you had a weight gain early in life in the absence of weight gain later, it would not be risky in terms of breast cancer," Calle tells WebMD. "But weight gain any time after 35 is very predictive of postmenopausal breast cancer."

Hormone Therapy, Weight Gain, and Breast Cancer

Breast cancer risk was linked to weight gain only in women not taking menopausal hormone therapy. That, Ahn says, is because hormone therapy itself increases a woman's risk of breast cancer. Hormone therapy apparently "masked" the effects of weight gain.

Why might this be so? Ahn and Calle note that fat tissue produces estrogen. Healthy young ovaries produce a lot more estrogen than fat tissue does, so estrogen from fat isn't a big issue early in a woman's reproductive years.