Background: Adequate 25(OH)D levels are required to prevent adverse effects on bone health. Population-based data on factors associated with 25(OH)D levels of people with MS have been lacking.
Objectives: To examine the prevalence and determinants of vitamin D insufficiency in a population-based sample of MS cases and controls, and to compare 25(OH)D status between MS cases and controls, taking into account case disability.
Methods: We conducted a population based case-control study in Tasmania, Australia (latitude 41-43 degrees S) on 136 prevalent cases with MS confirmed by magnetic resonance imaging and 272 community controls, matched on sex and year of birth. Measurements included serum 25(OH)D, sun exposure, skin type, dietary vitamin D intake and disability including EDSS.
Results: A high prevalence of vitamin D insufficiency was found in MS cases and controls. Among MS cases, increasing disability was strongly associated with lower levels of 25(OH)D and with reduced sun exposure. Cases with higher disability (EDSS > 3) were more likely to have vitamin D insufficiency than controls (OR = 3.07 (1.37, 6.90) for 25(OH)D </= 40 nmol/l), but cases with low disability were not (OR = 0.87 (0.41, 1.86)).
Conclusion: The strong associations between disability, sun exposure and vitamin D status indicate that reduced exposure to the sun, related to higher disability, may contribute to the high prevalence of vitamin D insufficiency found in this population-based MS case sample. Active detection of vitamin D insufficiency among people with MS and intervention to restore vitamin D status to adequate levels should be considered as part of the clinical management of MS.