According to the hygiene hypothesis, being too clean is not a good thing. Infections at an early age actually trains the immune system to respond appropriately to the environment, and this protects kids against certain diseases like asthma and MS, so the argument goes. Having older brothers and sisters should raise the odds of such infections, and therefore reduce the risk of MS...
Late birth order did not cut the risk of MS, the researchers report in the online issue of The Lancet Neurology medical journal. In fact, in large families with only one affected sibling, there was some evidence that late birth order actually raised the risk, as affected siblings were slightly younger than unaffected siblings. "This study does not support the prediction of the hygiene hypothesis," the team concludes.
technorati tags: multiple sclerosis, hygiene hypothesis