Ultraviolet radiation, vitamin D intake and multiple sclerosis

Abstract

Background: Multiple Sclerosis (MS), an inflammatory and neurodegenerative disease, has an elusive etiology that is thought to be an interaction between genetic and environmental risk factors. Ultraviolet Radiation (UVR) and/or vitamin D have been consistently shown to be protective against MS development; however, their roles in modulating the clinical course of this disease remain unclear. Objectives: The overall objective of this dissertation was to examine the effects of UVR and vitamin D related exposures on the ages of disease onset and progression to disability among a national cohort of Veterans with MS. Methods: We conducted a cross-sectional study, using a questionnaire designed to assess the different parameters that contribute to UVR exposure and vitamin D synthesis. We examined the dual influence of (1) timing and geographical location of birth and (2) sun exposure and vitamin D-related intakes from childhood to MS onset on the clinical course of this disease. All the analyses were conducted by disease subtype (Relapsing vs. Progressive MS). Multiple linear regression and Cox proportional hazard models were used to analyze the data. Results: Among Veterans with Relapsing MS (N=731), those born in winter and in low solar radiation areas, had their disease symptom onset on an average 2.8 years earlier (p = 0.02) than those born during other seasons in areas with medium to high solar radiation. Among 948 veterans with Relapsing MS, we found that low sun exposure in fall/winter seasons during childhood and early adolescence was also associated with early MS onset (p = 0.01); whereas regular use of cod liver oil in childhood was associated with later disease onset (p = 0.01). Among Veterans with progressive MS (N=151), low average fall/winter sun exposure before symptom onset was associated with an increased risk of disability (p = 0.01); while regular intake of cod liver oil during childhood and early adolescence decreased the risk (p = 0.04). Conclusions: Our findings suggest that environmental exposures before MS onset, primarily related to UVR and/or vitamin D status, early in life and during childhood and early adolescence have significant effects on the clinical course of MS.