By Eleanor McDermid
Three studies published in Neurology add weight to the theory that vitamin D levels have an important effect on relapse rates and cerebral lesions in patients with multiple sclerosis (MS).
Two of the studies provide conflicting evidence on whether vitamin D status interacts with interferon-β treatment.
The findings are important in the context of previous research showing an etiologic role for vitamin D in MS, say editorialists Alberto Ascherio (Harvard School of Public Health, Boston, Massachusetts, USA) and Ruth Ann Marrie (University of Manitoba, Winnipeg, Canada).
But they stress that proving causality is a "particularly daunting task" in the case of vitamin D and MS, because of the influence of season, time spent outdoors, and sun-protection behaviors.
The study by Trygve Holmøy (Akershus University Hospital, Lørenskog, Norway) and team had a cross-sectional design. It showed that, among 88 patients, each 10 nmol/L increase in vitamin D level at the time of magnetic resonance imaging was associated with a 12.7% reduction in the likelihood for new T1 gadolinium-enhancing lesions and a 11.7% reduction in the likelihood for new T2 lesions.
The effect was evident across 6 months before patients started interferon-β treatment, but not during the 18 months after.
In the second study, Rogier Hintzen (Erasmus Medical Center, Rotterdam, the Netherlands) and colleagues monitored 73 patients for an average of 1.7 years, during which they collectively had 139 clinical relapses. Vitamin D measurements were taken every 8 weeks and a doubling of levels was associated with a 27% reduction in relapse risk.
But Ascherio and Marrie comment that, with such frequent measurements, the results could reflect the effect of disease status on vitamin D levels, rather than the reverse.
The third study, by Bruce Taylor (University of Tasmania, Hobart, Australia) and team found a 10% reduction in rate of relapse for each 10 nmol/L increase in vitamin D levels among 178 patients over an average 2.2 years of follow up. In this study, vitamin D levels were measured every 6 months.
Contrary to the results of Holmøy et al, the researchers found the effect of vitamin D was evident only among patients taking interferon-β.
"For clinicians and their patients the fundamental question is whether otherwise adequate vitamin D levels for the general population are suboptimal for individuals with MS," say Ascherio and Marrie.
Published and ongoing trials do not sufficiently answer this question, they say, so it is "too soon to recommend the use of high-dose vitamin D in clinical practice."
But they advise "monitoring of vitamin D levels and supplementation as needed to achieve at least a year-round level of vitamin D sufficiency in persons with MS."
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