There was a 39% reduced risk for MS when levels of 25-hydroxyvitamin D (25[OH]D) increased 50 nmol/L (relative risk [RR] 0.61; 95% CI, 0.44-0.85; P =.003). A 25(OH)D level <30 nmol/L was associated with a 43% greater risk for MS compared with levels that were ≥50 nmol/L (RR 1.43; 95% CI, 1.02-1.99, P =.04). In addition, a 25(OH)D level of <30 nmol/L vs ≥50 nmol/L was associated with a 2-fold greater risk for MS in women who had ≥2 serum samples (RR 2.02; 95% CI, 1.18-3.45, P =.01).
This study failed to adjust for MS risk factors such as body mass index, smoking, or the presence of the Epstein-Barr virus infection, which might have limited the findings. In addition, the Finnish Maternity Cohort included primarily white subjects, which may reduce the findings’ applicability to other races.