Women who have high vitamin D levels are at a decreased risk for developing multiple sclerosis (MS), shows research.
In a study of Swedish women, 25-hydroxyvitamin D (25[OH]D) levels of at least 75 nmol/L were associated with a 61% decreased risk for developing the condition relative to levels lower than this.
However, in contrast to previous research, there was no evidence for a link between women's levels of 25(OH)D during gestation and children's future risk for MS, report Jonatan Salzer (Umea University, Sweden) and colleagues.
"Spring births have been associated with a higher risk of MS, and vitamin D deficiency during winter pregnancies has been suggested as a possible explanation for this," explains the team. "During part of the winter at latitudes =42° N, most UVB [ultraviolet bands] is absorbed by the atmosphere and no vitamin D is produced in the skin."
In a case-control study of two population-based biobanks including samples collected for 164,000 patients since 1975 in the north of Sweden (situated between latitudes 61.5°N and 69.1°N), the team identified 192 cases of individuals who had developed MS over a median of 9 years since their blood was sampled. They also identified 37 samples from pregnant mothers whose offspring had later developed MS.
Overall, the 25(OH)D levels were low, report Salzer et al. Only seven (4%) of 192 MS cases and 30 (8%) of 384 matched controls had 25(OH)D levels of 75 nmol/L or more.
As reported in Neurology, having 25(OH)D levels of at least 75 nmol/L was associated with a significantly reduced risk for the onset of MS, at an odds ratio of 0.39.
Among the gestational 25(OH)D samples, the team found no association between vitamin D status and MS risk.
However, a post-hoc analysis showed that the prevalence of 25(OH)D levels of at least 75 nmol/L among pregnant controls gradually fell between 1976 and 2005, implying that "the recommendation for vitamin D supplementation during pregnancy might need to be reviewed, especially since the vitamin D requirements during pregnancy may be higher than in the general population," writes the team.
"If the finding of decreasing 25(OH)D levels over time is representative of the entire population, perhaps it is key to why MS incidence is increasing," they add.
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