The benefits of breast-feeding for babies have proved to be myriad, and an increasing number of studies are finding long-term health benefits for mothers, too, including reduced risk of cardiovascular disease and lower odds of some cancers.

A new analysis confirms earlier observations that breast-feeding helps to decrease a mother's risk of developing type 2 diabetes, and suggests that even a single month of lactation can serve a protective effect. Many major U.S. medical organizations currently recommend breast-feeding infants for at least six months.

Researchers behind the new work found that mothers who did not breast-feed at all had about twice the chance of developing type 2 diabetes than mothers who did, even after controlling for other factors, such as age, race and health history. Twenty-seven percent of the mothers who reported not having breast-fed for at least a month had developed type 2 diabetes.

The protective effect against diabetes may surprise many people. "Diet and exercise are widely known to impact the risk of type 2 diabetes, but few people know that breast-feeding also reduces mothers' risk of developing the disease later in life," Eleanor Schwarz of the University of Pittsburgh's Department of Medicine and lead author of the study, said in a prepared statement.

The population-based study asked 2,233 women ages 40 to 78 about their breast-feeding and health history and calculated their body mass index. About two thirds (62 percent) of the women said they had breast-fed a baby for at least a month. And those who reported either having breast-fed exclusively for at least one month or at least in part for six months or more all had lower rates of diabetes than mothers who never breast-fed—but about the same rates as women who had never given birth.

Whereas much previous research has suggested at least six months of lactation was needed for substantial protective effects, the new data "showed significant benefits with only one month of lactation," reported the researchers.

Scientists are still working to understand the mechanisms behind this pattern. Schwarz and her colleagues noted that women who breast-feed tend to be faster to shed the additional visceral fat gained during pregnancy, and animal studies have shown that breast-feeding might increase a woman's insulin sensitivity. Women with a higher risk for diabetes might also be less inclined to breast-feed, the authors noted. "Studies have linked obesity and insulin resistance to difficulties with breast-feeding," and in the study, women who were obese were less likely to have breast-fed.

The findings were published online August 27 in The American Journal of Medicine.

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