Older women who put on a significant amount of weight are at higher risk for breast cancer

Researchers have suspected for some time that women who weigh more have an increased risk for several kinds of cancer. Now some new data strengthens that assertion. It shows that weight gain throughout adulthood significantly increases women's risk of developing breast cancer.

Researcher Jiyoung Ahn from the U.S. National Cancer Institute examined data from a study that's been following the progress of close to one 100,000 post-menopausal women. The Diet and Health study has been looking at the relationship between the two for more than a decade. Researchers started collecting data in 1996, with extensive questionnaires. Ahn explains, "The women reported their current weight plus their weight at ages 18, 35 and 50, which corresponds to early reproductive years, late reproductive years and postmenopausal years."

Ahn says through the year 2000, about 2000, or 2 percent, of these women developed breast cancer. She says that rate is comparable to the rate of breast cancer in the general American population.

The researchers found a direct correlation between the amount of weight gained and increased risk for breast cancer. "Women who gained about 20 to 30 kilograms during their total adulthood, which is equivalent to 40 to 60 pounds, had a 1.5 times increased risk of breast cancer compared with women who maintained their weight," Ahn says.

The more weight that women gained, the higher their breast cancer risk. And if women gained 50 kilograms, their breast cancer risk more than doubled. Other known risk factors for breast cancer are late menopause, late age at first birth, not having had a baby, or drinking moderate to heavy amounts of alcohol. Ahn says even though her research team controlled for these other risk factors when they did their calculations, extra weight added extra risk.

She says the issue might be exposure to estrogen, explaining, "Estrogen is produced in fat tissue. Increased breast cancer risk associated with weight gain may be due to women's increased exposure to estrogen released from fat tissue."

The National Cancer Institute's diet and health study is ongoing. Ahn says next, she'll be examining other data that may reveal the links between what we eat and our cancer risk.

Her paper is published in the Archives of Internal Medicine.