Diabetes Tied to Increased
Risk of Breast Cancer
Excerpt By Jacqueline Stenson, Reuters Health

Women with diabetes may have a slightly elevated risk of developing breast cancer, new study findings suggest.

"We found there is a small but statistically significant association," said study author Dr. Karin B. Michels, an associate professor of epidemiology at Harvard Medical School in Boston.

The results, drawn from the ongoing Nurses' Health Study, showed that women with type 2 diabetes were 17 percent more likely to develop breast cancer than those without diabetes. Type 2 diabetes, the most common form of the disease, usually develops in adulthood though it is on the rise in children, who are increasingly becoming overweight.

In their analysis, Michels and colleagues accounted for various factors that may have influenced the results, such as heavy alcohol consumption, obesity and a family history of breast cancer.

The research involved 116,488 female nurses who were ages 30 to 55 when the study began in 1976. They were followed for the next two decades, during which time there were 6,120 cases of type 2 diabetes and 5,605 cases of breast cancer. Of those who developed breast cancer, 202 had diabetes.

The link between diabetes and breast cancer was apparent in postmenopausal but not premenopausal women, according to findings reported in the June issue of the journal Diabetes Care.

Michels said the explanation for the association between the two diseases is not clear. "How all of this works mechanistically we're not entirely sure," she told Reuters Health.

Some investigators have speculated that elevated levels of insulin in the blood of diabetics may somehow promote breast cancer, the study authors note in the report.

Insulin is a hormone produced by the pancreas that allows glucose, or blood sugar, to enter cells to be converted into energy. This process is impaired during insulin resistance, when the body becomes less sensitive to the effects of insulin, prompting the pancreas to pump out more insulin to try to compensate.

Efforts to prevent diabetes by encouraging people to exercise regularly, control their weight and eat a healthful diet may have a new, added benefit for women, according to Michels.

"Maybe we can prevent some breast cancers as well," she said.

SOURCE: Diabetes Care 2003;26:1752-1758.

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