Contrary to what the “hygiene hypothesis” suggests, the youngest children in a family are not less likely than older siblings to develop multiple sclerosis, new research suggests.
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.
To look into this idea, Dr. A. Dessa Sadovnick, from the University of British Columbia in Vancouver, Canada, and colleagues analyzed data from 10,995 MS patients and 26,336 healthy siblings drawn from a large population-based registry.
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.
