Mothers who breastfeed their children may have a lower risk of developing Alzheimer's disease.
The report, published in the Journal of Alzheimer's Disease, suggests that the link may be to do with certain biological effects of breastfeeding and that longer periods of breastfeeding lowered the overall risk.
Previous studies have established that breastfeeding can reduce a mother's risk of other diseases but until now little has been done to examine the impact of breastfeeding duration on Alzheimer's risk.
Dr Molly Fox, from the department of biological anthropology at the University of Cambridge, led the study.
She said: "Alzheimer's is the world's most common cognitive disorder and it already affects 35.6 million people.
"So it is vital that we develop low-cost, large-scale strategies to protect people against this devastating disease."
Although researchers used data from a very small group of 81 British women, they say they observed a highly significant and consistent correlation between breastfeeding and Alzheimer's, although the connection was much less pronounced in women who had a family history of dementia.
The findings may point towards new directions for fighting the global Alzheimer's epidemic.
The study argues that there may be a number of biological reasons for the connection between Alzheimer's and breastfeeding.
One theory is that breastfeeding deprives the body of the hormone progesterone, compensating for high levels of progesterone that are produced during pregnancy.
Progesterone is known to desensitise the brain's oestrogen receptors, and oestrogen may play a role in protecting the brain against Alzheimer's.