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Acta Neurol Scand. 2010 Jan;121(1):20-3. doi: 10.1111/j.1600-0404.2009.01181.x. Epub 2009 Nov 23.

Season of birth and multiple sclerosis in Sweden.

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Department of Neurology, Umeå University Hospital, Umeå, Sweden.

Corrected and republished in



To estimate the risk of multiple sclerosis (MS) by month of birth in Sweden.


Cases (n = 9361) were obtained from the Swedish MS Registry. All births in Sweden 1900-2007 served as controls (n = 12,116,853). The risk of MS was analyzed for each month of birth separately compared with birth during the other 11 months.


More (11%) cases with MS than expected were born in June. Fewer (8% and 10%) cases with MS than expected were born in December and January (non-significant after correction for multiple analyses). More (5%) cases with MS than expected were born in February-July as compared with August-January.


This study supports previous results suggesting an association between the risk of MS and the season of birth. Decreased exposure to sun in the winter leading to low vitamin D levels during pregnancy is a possible explanation that needs further research.

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