"Various studies suggest that breastfeeding affects women's metabolism, and that prompted us to look at whether lactation does something in terms of diabetes risk," Dr. Alison M. Stuebe of Brigham and Women's Hospital and Harvard Medical School in Boston told Reuters Health. "Those studies show that metabolism, lactation, and reproduction are all tied together in a potentially interesting way

To look for associations between lactation duration and the development of type 2 diabetes, Stuebe and her colleagues analyzed data from two large groups of women who had given birth. The first group included 83,585 women who were part of the Nurses' Health Study, and the second group included 73,418 women who were part of the Nurses' Health Study II. "The second group is a younger group," said Stuebe.

The researchers found that in the first 15 years after a woman's last delivery, each year of breastfeeding was associated with a 15-percent reduction in her risk of diabetes. "In that analysis, we took into account diet, exercise, smoking status, whether or not the women took multivitamins -- which is a marker of whether they are health-conscious or not -- and we still found that 15-percent benefit," remarked Stuebe.

"Beyond 15 years after the last birth there wasn't so much of a benefit, but for at least the first 15 years there seems to be some long-term association that protects women from diabetes," she added.

"In some way, pregnancy is a pro-diabetic state; you have more resistance to insulin, and that's part of the way the body makes sure that the fetus gets enough sugar," explained Stuebe. "Then comes lactation which, in a sense, is an anti-diabetic state."

The researchers' hypothesis is that lactation resets the body after pregnancy. If a woman does not breastfeed for a prolonged period of time, the risk of diabetes might increase.

For Stuebe, one of the nicest things about these findings is that there is no downside to breastfeeding. "It gives us more reasons to encourage women to breastfeed: it's good for babies and it's good for mothers," she concluded.

SOURCE: The Journal of the American Medical Association, November 23/30, 2005, Rueters health