Low blood levels of vitamin D are tied to poorer cognitive skills and more severe disability in people with multiple sclerosis, researchers in Italy report.
“Our study showed that [vitamin D] levels are associated with cognitive function in MS, as already well demonstrated in the general population and in neurodegenerative diseases” such as such as Parkinson’s and Alzheimer’s, they wrote.
“In particular, we demonstrated that, in MS, vitamin D levels are associated with attention/information processing speed … and with working and verbal memory,” suggesting vitamin D may have a protective role in MS, the scientists added.
The study, “Low serum 25‑hydroxy-vitamin D levels are associated with cognitive impairment in multiple sclerosis,” was published in the journal Multiple Sclerosis and Related Disorders.
Vitamin D levels previously linked with MS motor disability, disease activity
While difficulties with walking, balance, and fatigue are among the most common MS symptoms, problems with cognition also are evident in a disease caused by mistaken immune system attacks on the protective covering of nerve fibers in the brain and spinal cord.
“Attention, information processing speed, and visuospatial memory are the most commonly affected domains in MS,” the researchers wrote. Information processing speed is the time needed to understand and respond to information, and visuospatial memory is a part of working memory that’s needed for orientation, and depth and distance perception.
Vitamin D, mostly known for its role in maintaining bone health, also is involved in brain and muscle health. Previous studies suggest that vitamin D deficiency may contribute to MS development and progression.
“Low vitamin D has been associated with cognitive dysfunction in different neurodegenerative diseases, and, in MS, with motor disability and disease activity,” the researchers wrote.
Emerging evidence also suggests that low vitamin D levels may link with slower processing speed in people in earlier MS stages, but how they might affect other areas of cognition is unclear.
Researchers in Italy recruited 181 adults with an MS diagnosis, being followed at a university hospital’s MS center in Naples and given a Brief International Cognitive Assessment for MS (BICAMS) exam there between January and April 2022. Measures of their vitamin D blood levels also were collected the day of that exam.
BICAMS includes the Symbol Digit Modalities Test (SDMT) to assess information processing speed, the California Verbal Learning Test-II (CVLT-II) of working and verbal memory, and the Brief Visuospatial Memory Test-Revised (BVMT-R).
It is “a widely used battery that explores the cognitive domains most commonly affected in MS,” the researchers wrote.
Patients had mean vitamin D levels below that considered sufficient
Patients’ mean age was 46.8, and more than half (61.3%) were women. Most (73.5%) had relapsing-remitting MS, 33 (18.2%) had secondary progressive MS, and 15 (8.3%) had primary progressive MS.
Their median score on the Expanded Disability Status Scale (EDSS) was 3.5; this standard measure of MS-related disability ranges from zero to 10, with higher scores indicating greater disability.
Patients’ mean vitamin D blood levels were 24.2 nanograms per milliliter (ng/mL), with adequate vitamin D levels defined as 31 ng/mL or higher. More than one-third of the group (39.3%) had vitamin D deficiency, or levels below 20 ng/mL; and another 35.5% had vitamin D insufficiency, with levels ranging 20 to 30 ng/mL.
A lower vitamin D level significantly associated with poorer cognitive function, the researchers found. In particular, the vitamin D level was 9.63 ng/mL lower for each BICAMS test showing cognitive impairment.
“In our study, we confirmed previous associations between attention/information processing speed on SDMT and vitamin D levels, and also found an association with verbal memory (CVLT-II),” the researchers wrote.
After adjusting for potential influencing factors, they found that vitamin D levels were 0.7 ng/mL higher for each unit increase in the SDMT scores, indicating faster information processing. Vitamin D levels also were 0.1 ng/mL higher for each unit increase in the CVLT-II, reflecting better working and verbal memory.
While these associations were statistically significant, no significant link was found between vitamin D levels and BVMT-R scores.
Depression, fatigue levels not seen to affect study’s findings
Vitamin D blood levels also significantly associated with EDSS scores, being 2 ng/mL lower for each unit increase in the EDSS, indicating more disability.
These associations remained significant when the scientists adjusted their analyses to account for patients’ depression, anxiety, and fatigue levels, which can affect cognitive function and test performance.
“Vitamin D is associated with both motor and cognitive disability in MS, thus suggesting its relationship with neurodegenerative aspects of the disease,” the researchers wrote, noting “these associations are not influenced by depression, anxiety and fatigue.”
Future studies following patients over time are needed to confirm these findings and clarify the link between vitamin D and cognitive function in MS.
