Low levels of vitamin D can increase MS risk but low gestational levels of 25(OH)D have no effect on MS risk.
AMSTERDAM—Levels of vitamin D greater than or equal to 75 nmol/L are associated with a 61% lower risk for multiple sclerosis (MS), researchers reported at the Fifth Joint Triennial Congress of the European and Americas Committees for Treatment and Research in Multiple Sclerosis. Gestational vitamin D levels do not affect the risk for MS in children, however.
Jonatan Salzer, a graduate student in clinical neuroscience at Umeå University in Sweden, and associates conducted a study to estimate the risk for MS by examining levels of 25(OH)D in prospectively collected blood samples from patients with MS and controls. The investigators also sought to evaluate the risk for MS in children by studying levels of 25(OH)D during pregnancy.
The researchers created a database of MS cases and mothers of patients with MS in the four northern counties of Sweden. The database was cross-linked to various biobanks that contained serum and plasma samples taken between 1976 and 2005. The researchers found 192 MS cases with prospectively collected samples for their study of risk factors of MS, and 37 gestational samples taken during pregnancies in which the offspring had later developed MS, as the basis for their inquiry into gestational risk factors of MS. Controls were matched for sex, biobank, sampling date, and age.
Decreasing Levels of Vitamin D
Analysis showed that 3.6% of MS cases and 7.8% of controls had levels of 25(OH)D ≥75 nmol/L, which is the cutoff for normal levels, as defined by the American Endocrine Society. The investigators found a negative correlation between 25(OH)D levels and sampling year for samples collected from May through October (ie, the 25(OH)D levels were lower in later samples).
Also, the risk for 25(OH)D levels <75 nmol/L in controls was three times higher in samples taken after 1985 than it was in samples taken before 1985. Overall, the risk of having 25(OH)D levels <75 nmol/L increased from 1976 to 2005, according to Mr. Salzer.
Changes in the population’s summer behavior, including increasing use of sunscreen, wearing clothes that cover more of the body, and a reduction in time spent outdoors, could explain the overall decrease in vitamin D levels, said Mr. Salzer. “If this finding can be replicated in other cohorts, and applies to the time before 1976, perhaps it is the key to why MS incidence is increasing,” he added.
No effect on MS risk was observed when the investigators grouped 25(OH)D levels into other categories, such as median, tertiles, and quintiles. This result occurred “because of the high prevalence of 25(OH)D levels <75 nmol/L in northern Sweden” and “suggests that higher levels are needed to protect against MS,” said Mr. Salzer.
The results contradict the findings of the 2011 diet questionnaire study conducted by Mirzaei et al. The investigators noted that their results “must be treated with caution,” however, because of the small sample size. “There is a need for expanded study material on vitamin D levels, in which samples are collected from gestation through adolescence,” Mr. Salzer said.
A Call to Revise Recommended Doses of Vitamin D
It may be reasonable to “adjust the supplementation recommendations to increase the doses and include the entire population, with the goal of no one having levels below 75 nmol/L” concluded Mr. Salzer.
—Erik Greb