Vitamin D intake and multiple sclerosis risk in the Norwegian Mother, Father and Child cohort.

BACKGROUND

Higher vitamin D has consistently been associated with a lower multiple sclerosis (MS) risk, but some controversy remains about whether this is due to vitamin D itself or sunlight.

METHODS

We conducted a prospective study among women participating in the Norwegian Mother, Father and Child Cohort Study, recruited in 2002-2008 and followed until 2022. We identified incident MS cases through data linkage with the Norwegian MS Registry. Total vitamin D intake from food and supplements was obtained from validated food frequency questionnaires completed in pregnancy. We estimated HRs for MS and 95% confidence intervals (CI) using Cox regression.

RESULTS

Among 78 074 participants, 349 developed MS during follow-up. Their median daily vitamin D intake was 296 international units (IU) compared with 333 IU among women who did not develop MS. Higher total vitamin D intake was associated with a 42% lower MS risk (HR comparing top vs bottom quintile 0.58, 95% CI 0.38 to 0.89, ptrend<0.01). The results were similar when adjusting for age at delivery, total energy intake, pre-pregnancy body mass index and smoking. The associations were similar for vitamin D intake from food (HR for top vs bottom quintile 0.70, 95% CI 0.47 to 0.1.04, ptrend=0.02) and supplements (HR for ≥600 IU/day vs <200 IU/day 0.65, 95% CI 0.41 to 1.04, ptrend=0.01).

CONCLUSIONS

In this prospective study, higher vitamin D intake was associated with lower MS risk in women living in Norway, where there is insufficient sun-induced vitamin D production during most of the year. This supports the hypothesis that vitamin D itself modifies MS risk.