Exposure to younger siblings’ infections during the first six years of life appears to help develop elder children’s immune systems and cut their risk of multiple sclerosis.
To test the “hygiene hypothesis” -- that infections early in life may reduce the risk of developing allergies and autoimmune diseases in adulthood -- Australian researchers looked at the histories of 136 Tasmanian adults with multiple sclerosis and compared them with 272 without the disease. Those who as children had up to five years of contact with a younger sibling had an 88% reduced risk of developing multiple sclerosis. Those with one to three years of exposure had a 43% reduced risk. Longer exposure to a younger sibling also translated into a lower risk of developing mononucleosis.
The research was published in the Jan. 26 issue of the Journal of the American Medical Assn.