25-Hydroxyvitamin D deficiency and risk of MS among women in the Finnish Maternity Cohort.

OBJECTIVE

To determine whether and to what extent vitamin D deficiency is associated with multiple sclerosis (MS) risk.

METHODS

We conducted a prospective nested case-control study among women in the Finnish Maternity Cohort (FMC). The FMC had 1.8 million stored serum samples taken during the pregnancies of over 800,000 women at the time of this study. Through linkages with hospital and prescription registries, we identified 1,092 women with MS diagnosed between 1983 and 2009 with at least 1 serum sample collected prior to date of MS diagnosis; ≥2 serum samples were available for 511 cases. Cases were matched to up to 3 controls (n = 2,123) on date of birth (±2 years) and area of residence. 25-Hydroxyvitamin D (25[OH]D) levels were measured using a chemiluminescence assay. We used conditional logistic regression adjusted for year of sample collection, gravidity, and parity to estimate relative risks (RRs) and 95% confidence intervals (CIs).

RESULTS

A 50 nmol/L increase in 25(OH)D was associated with a 39% reduced risk of MS (RR 0.61, 95% CI 0.44-0.85), = 0.003. Women with 25(OH)D levels <30 nmol/L had a 43% higher MS risk (RR 1.43, 95% CI 1.02-1.99, = 0.04) as compared to women with levels ≥50 nmol/L. In women with ≥2 samples, MS risk was 2-fold higher in women with 25(OH)D <30 nmol/L as compared to women with 25(OH)D ≥50 nmol/L (RR 2.02, 95% CI 1.18-3.45, = 0.01).

CONCLUSIONS

These results directly support vitamin D deficiency as a risk factor for MS and strengthen the rationale for broad public health interventions to improve vitamin D levels.