Vitamin D Deficiency Linked to Early Cognitive Difficulties in Study

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by Steve Bryson, PhD |

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Low vitamin D levels in the bloodstream are associated with slower information processing speeds in people with early-stage multiple sclerosis (MS), a study suggests.

“Our data support the hypothesis that vitamin D is involved in cognition in MS,” its researchers concluded.

The study, “Serum Vitamin D as a Marker of Impaired Information Processing Speed and Early Disability in Multiple Sclerosis Patients,” was published in the journal Brain Sciences.

In MS, immune attacks against myelin — the protective coating around nerve fibers — result in inflammation that further damages nerve fibers, disrupting electric signals traveling from the brain to the body and back.

Patients experience various symptoms that can include numbness and tingling, muscle spasms, walking difficulties, pain, fatigue, and bowel or bladder problems. Emotional changes such as depression, anxiety, and mood swings are also known.

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Cognitive impairment was initially thought to appear only in the progressive types of MS. But recent evidence suggests that changes to cognition affect MS patients across disease stages, including onset.

In particular, one of the first cognitive problems seen in MS is a slowing in information processing speed — the time needed to understand and respond to information — relative to others without the condition.

Vitamin D is involved in several cellular processes, from regulating bone density to the immune system, as well as in promoting nerve cell survival by reducing pro-inflammatory signals.

A lack of vitamin D has been associated with a higher risk of MS and greater disease activity. Likewise, an association between low vitamin D levels and cognitive impairment has been established in other neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease.

However, several MS clinical trials failed to show vitamin D supplements as an effective add-on therapy, and few studies have explored the relationship between vitamin D and information processing speed in the early stages of MS.

Researchers at the University of Piemonte in Italy examined whether a correlation exists between vitamin D and information processing speed in 81 newly diagnosed MS patients. All had at least one year of follow-up.

Eligible patients had vitamin D levels measured at diagnosis and, at the same time, underwent the symbol digit modalities test (SDMT) to assess information processing speed as part of the Brief International Cognitive Assessment in MS patients (BICAMS).

As sunlight affects vitamin D levels, patients were enrolled at two northwestern Italian regions with similar climates, then categorized into spring/summer and autumn/winter sampling to ensure similar exposure. Vitamin D was measured in blood serum, the fluid component of blood without clotting factors.

Their mean age at diagnosis was 37.6, and most in this group — 54 or 67% — were women. Most, 71, patients had relapsing-remitting MS (RRMS), two had clinically isolated syndrome (CIS), one was a primary progressive MS (PPMS) patient, while seven had radiologically isolated syndrome (RIS), characterized by nerve damage indicative of MS without any clinical signs of the disease.

Low vitamin D levels were found in most of these patients, with a mean of 19.71 nanograms per mL of serum (ng/mL).  A total of 10 people had vitamin D levels of 30 ng/mL or greater, which are considered within normal range.

Vitamin D levels sampled in the winter in a group of 48 patients showed no mean differences from those of 33 participants sampled in the summer.

A total of 18 patients, 21.95% of this group, had slowed information processing speed, including 15 with RRMS and one each with RIS, CIS, and PPMS. Those with low vitamin D levels scored significantly lower on the SMDT assessment compared with those with vitamin D in the normal range. None of the participants with cognitive impairment had normal vitamin D levels.

The relationship between low vitamin D and slower information processing speed was confirmed by statistical analysis, after adjusting for sunlight exposure and MRI parameters.

Compared with patients with normal vitamin D levels, those with low levels also had worse disease severity at both diagnosis and at their last clinical follow-up, as evaluated by the expanded disability status score (EDSS).

Patients with gadolinium-enhancing lesions in MRI, which are lesions with active inflammation, or spinal cord involvement did not have slower information processing speeds. In contrast, those with a greater volume of brain white-matter lesions, reflecting more damage to myelin, had poorer SDMT test scores.

Additional analyses found that the most significant predictors of SDMT scores were vitamin D levels, educational achievement, and age at diagnosis. After adjusting for EDSS, the type of MS, and MRI characteristics, vitamin D levels remained the only predictor of information processing speeds, the researchers noted.

“Our study supports the hypothesis that vitamin D may influence cognition and disability from the early stages of MS disease,” they concluded.