The researchers enrolled 23 patients with relapsing-remitting MS and secondary progressive MS. After laboratory work to determine serum vitamin D levels, patients underwent a comprehensive neuropsychological evaluation to assess emotional functioning, memory, executive functioning, processing speed, attention, and visuospatial abilities.

Low vitamin D levels and poor performance were correlated on a verbal learning test (r = .49; P < .05). The effect was stronger in single-trial learning (r = .65; P < .001). No correlation was observed during later learning trials.

"These findings suggest the importance of determining vitamin D levels in order to maximize cognitive potential among MS patients. Future randomized trials should examine whether vitamin D supplementation may improve learning in MS," the researchers wrote in the abstract.

The work was prompted by several recent studies that showed a relationship between cognitive function and vitamin D levels in the elderly, Todd Feaster, PsyD, a neuropsychologist at the MidAmerica Neuroscience Institute in Lenexa, Kansas, told Medscape Neurology. Dr. Feaster also works with patients with Alzheimer's disease, so those findings struck a chord in him, he said.

The study suggests that cognitive impairment might not be caused by MS alone but could be caused or exacerbated by vitamin D deficiency, and supplementation might improve symptoms.

"When you have a winter like we've had in the Midwest, you're stuck inside all day. So is vitamin D deficiency exacerbating cognitive issues? And if we get those levels up, will we get improvement?" Dr. Feaster posited.

The study was relatively small, cautioned Helen Tremlett, PhD, assistant professor of neurology at the University of British Columbia in Vancouver, Canada. "It does need to be reproduced," she told Medscape Neurology.

"He didn't factor in seasonality, which could be [important]. But if the findings are true, we might be able to supplement vitamin D and bring up cognitive levels" in these patients, Dr. Tremlett suggested.

However, the study isn't robust enough to change clinical practice just yet. "We can't do an intervention based on what he's presented, but it gives us real food for thought. A longitudinal study would be nice to see," she remarked.

Consortium of Multiple Sclerosis Centers (CMSC) 24th Annual Conference and the Third Joint Meeting of Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS): Abstract P03. Presented June 4, 2010.