VANCOUVER, British Columbia, Aug. 22 (UPI) -- A Canadian study finds that being an older child in a family does not increase the risk of developing multiple sclerosis.
Dessa Sadovnick of the University of British Columbia and George Ebers of Oxford University tracked 10,900 people with the degenerative disease and 26,300 healthy siblings. They found that birth order does not appear to affect risk of MS.
Some small studies had suggested that older siblings or people from smaller families had a higher risk. Researchers suggested that children with older siblings got some protection from being introduced to infections, known as the hygiene hypothesis.
"This study does not support the prediction of the hygiene hypothesis, which suggests that people with MS would be born earlier than expected within their sibships," Sadovnick said. "The data presented here cast no doubt on the importance of environmental factors to MS risk, and suggest that environmental risks for MS must be accounted for by factors that do not affect birth-order position."
The study was published in The Lancet Neurology.
