Document resource
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, p trend<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.