Time of birth, residential solar radiation and age at onset of multiple sclerosis.

UNLABELLED BACKGROUNDS/AIM: Gestational and early life events have been suggested to contribute to multiple sclerosis (MS) susceptibility. We assessed the effects of time and place of birth on the age at onset of MS symptoms. METHODS We selected a national cohort of 967 veterans from the Multiple Sclerosis Surveillance Registry for whom month and season (time) of birth, and birthplace (city and state) were available. Multiple linear regression analyses were used to examine the association between time of birth, birthplace latitude and solar radiation, and the age at onset of MS symptoms among the study sample. RESULTS Patients with a relapsing form of the disease (R-MS), who were born in winter and whose birthplace was in low solar radiation areas, had disease symptom onset on average 2.8 years earlier than those born in seasons other than winter and in medium- and high-solar radiation areas (p = 0.02). CONCLUSIONS These results suggest that exposure early in life to geographical and seasonal factors, possibly related to the protective effect of sunlight, and thus vitamin D, is associated with a delay in MS symptom onset. Other larger studies are required to examine the period-specific (from conception to adulthood) environmental factors that are associated with MS susceptibility.