The paper, published in the Journal of Alzheimer's Disease, suggested that the link may be to do with certain biological effects of breastfeeding. For example, breastfeeding restores insulin tolerance which is significantly reduced during pregnancy, and Alzheimer's is characterized by insulin resistance in the brain.

　　Although data was gathered from a group of just 81 British women, researchers observed a highly significant and consistent correlation between breastfeeding and Alzheimer's risk. They argued that this was so strong that any potential sampling error was unlikely.

　　"Alzheimer's is the world's most common cognitive disorder and affects 35.6 million people," said Dr. Molly Fox from the University of Cambridge, who led the study.

　　"In the future, we expect it to spread most in low and middle-income countries. So it is vital that we develop low-cost, large-scale strategies to protect people against this devastating disease," Fox said.

　　Previous studies have already suggested that breastfeeding can reduce a mother's risk of certain other diseases. Research has shown that there may be a link between breastfeeding and a woman's general cognitive decline later in life. Until now, however, little has been done to examine the impact of breastfeeding duration on Alzheimer's risk.