A small but provocative new study suggests that breastfeeding a baby may significantly reduce a woman's risk of developing Alzheimer's disease decades later.
Researchers at the University of Cambridge found that women who breastfed for at least one week had a 64 percent reduction in Alzheimer's risk compared to women who did not breastfeed at all. The study accounted for other possible lifestyle and socioeconomic factors, like smoking, drinking and education.
The study, published online in the "Journal of Alzheimer's Disease" on July 23, looked at the cumulative breastfeeding histories of 81 British women over age 70. Researchers interviewed family members as well, to ensure they were getting accurate recall of the past.
According to the study, the longer a woman breastfed, the greater the benefits.
Based on the findings, if one were to compare two hypothetical women who were identical in every way, but one breastfed for 12 months throughout her life, while the other breastfed for four and a half months, the woman who breastfed for a year would have a 22 percent lower risk of developing Alzheimer's than the other.
But the findings, while intriguing, are highly preliminary.
"This was a pilot study, in a small group of women, from one region, with one ethnic background. This question needs to be explored in other populations, in other places," cautioned Molly Fox, a researcher with the division of biological anthropology at the University of Cambridge and an author on the new study. "What's important to recognize, however, is that there does appear to be a relationship between breastfeeding history and Alzheimer's risk that needs to be further explored."
One intriguing finding is that the ratio of time women spent pregnant relative to the time they breastfed appeared to influence outcomes: Women who spent more time breastfeeding compared to time pregnant had a much lower risk of Alzheimer's.
However, the overall protective effects of breastfeeding disappeared when researchers focused on the 20-odd women in the study who had a parent or sibling with Alzheimer's.
It is unclear why breastfeeding might influence later cognitive function, although the researchers have theories. One possibility is that breastfeeding lowers the levels of progesterone in the body -- a hormone that is very high during pregnancy, and that desensitizes the brain's estrogen receptors. Earlier research suggests that estrogen helps protect the brain against Alzheimer's.
"Breastfeeding affects women's bodies in so many different ways," Fox said. "It has an impact on their ovarian hormones, their glucose metabolism, their inflammatory response -- and at the moment, we don't really know which of these pathways is the one that might be having an effect on women's brains decades down the road."
The new study is among the very first to look at the possible link between breastfeeding and cognitive issues specifically, but it joins a growing body of research emphasizing the health benefits of nursing for women, not just their babies. Breastfeeding has been linked to lower risk of type 2 diabetes, breast and ovarian cancer and postpartum depression.
Fox stressed that the researchers were limited in their ability to control for all outside factors that might account for the link between breastfeeding and lower risk of Alzheimer's -- a disease that affects 5.2 million Americans -- in part because researchers simply do not know all of the factors that contribute to the disease's development.
"So much medical research focuses on the genetic risk factors for Alzheimer's," she said. "But women's reproductive histories may also be an important influence."
The American Academy of Pediatrics recommends that women breastfeed exclusively for 6 months and a year or beyond while supplementing with food.