There are many studies that show that the risks for getting multiple sclerosis (MS) vary according to the month a person is born. However, the differences between the months of birth are slight.
For example, a 2005 study of people with MS living in northern latitudes found that more people (9.1%) had a birthday in May and significantly less (8.5%) were born in November. The opposite pattern is seen in the southern hemisphere. Thus, worldwide there is a slight increase in MS risk in those born in the spring and a decrease in those born in the winter.
The cause of this has not been determined. Some ideas include differences in:
Vitamin intake during pregnancy (more folate in fresh vegetables in the spring, more vitamin D from sunlight in the summer)
- Birth weight - Heavier babies born after summer and fall pregnancies
- Exposure to viruses - More people experience viruses in spring and fall. This may affect the not only the viruses a baby is exposed to during pregnancy, but also after birth.
A recent article in JAMA Neurology describes ...