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Does Vitamin D Reduce the Risk of Dementia?


 

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Three studies address whether vitamin D deficiency plays role in lowering the risk of dementia and slowing cognitive decline. Two studies say yes, while a third found no independent associations in men.

Insufficient levels of vitamin D were associated with all-cause dementia, Alzheimer’s disease, stroke, and MRI indicators of cerebrovascular disease, according to one of three related studies published in the January 5 Neurology. A second study found a link between cognitive impairment and vitamin D deficiency in older women. However, a third study found no independent association between lower levels of the vitamin and baseline global and executive cognitive function or incident cognitive decline in older men.

Increasing evidence suggests that vitamin D is associated with a number of pathophysiologic conditions such as age-related cognitive decline, according to Joshua W. Miller, PhD. “There is also evidence that vitamin D suppresses the expression of inflammatory cytokines, thus potentially connecting vitamin D deficiency to inflammatory and vascular disease mechanisms underlying neurodegeneration,” noted Dr. Miller, of the University of California–Davis Medical Center in Sacramento, in a commentary on the three studies. “With estimates that the prevalence of vitamin D deficiency in older adults may exceed 50% depending on time of year, living circumstances, dietary intake, and skin color, it is reasonable to postulate that vitamin D deficiency can contribute to age-related cognitive decline.”

Vitamin D and Dementia in Elders Receiving Home Care Women and Vitamin D

In a cross-sectional investigation of 25-hydroxyvitamin D [25(OH)D], dementia, and MRI measures of cerebrovascular disease in elders receiving home care between 2003 and 2007, Jennifer S. Buell, PhD, and colleagues found that more than half of those tested had either deficient (

After adjusting for age, race, sex, BMI, and education, the researchers found that 25(OH)D insufficiency was associated with increased risk for all-cause dementia (odds ratio [OR], 2.3), Alzheimer’s disease (OR, 2.5), and stroke (OR, 2.0). Individuals with dementia represented 23.9% (n=76) of subjects, 41 of whom were classified as probable Alzheimer’s disease. Mean 25(OH)D levels were lower in subjects with dementia and there was a higher rate of dementia among participants with 25(OH)D insufficiency (30.5% vs 14.5%).

“Approximately 30% of free-living elders with mild cognitive impairment are likely to develop dementia and require institutionalization,” noted Dr. Buell, of the Friedman School of Nutrition Science and Policy at Tufts University in Boston, and colleagues. “If the associations seen here are confirmed, maintenance of healthy vitamin D status could prove a cost-effective contribution toward preservation of cognitive dysfunction and support lengthened independent living for the elderly.”

A second study evaluated vitamin D levels and cognitive function in 752 women, ages 75 and older, who were randomly selected from the Epidémiologie de l’Ostéoporose (EPIDOS) cohort.

“Evidence collected over the last 30 years has shown that serum 25(OH)D could be associated with global cognitive performance, even if it remained unclear which specific cognitive functions were affected in vitamin D deficiency,” Cédric Annweiler, MD, MS, told Neurology Reviews.

Vitamin D and Cognition in Elderly Men

“After adjustments for educational level and race, there seemed to be no difference in effect size across the quartiles,” Dr. Slinin and colleagues wrote. “When only white participants were included, there was no association between 25(OH)D level and cognitive impairment by 3MS testing after adjusting for age, season, and site.”

Vitamin D-mentia?

Dr. Miller questioned whether vitamin D deficiency was a cause or an effect of cognitive impairment, noting that demented adults may have poor diets or lack sun exposure.

“What are needed now are placebo-controlled intervention studies to determine if vitamin D supplements will protect against age-related cognitive decline,” Dr. Miller wrote. “In the meantime, neurologists and geriatricians should be aware of the high prevalence of vitamin D deficiency in their patient populations and the possibility that supplementation could be beneficial.”

A third study failed to find strong independent associations between lower levels of vitamin D and cognitive function or decline. Yelana Slinin, MD, MS, of the Center for Chronic Disease Outcomes Research, VA Medical Center, Minneapolis, and colleagues measured 25(OH)D levels and assessed cognitive function using the Modified Mini-Mental State Examination (3MS) and Trail Making Test Part B (Trails B) in a random sample of subjects enrolled in the Osteoporotic Fractures in Men Study.

The investigators tracked cognition levels of 1,604 men for an average of 4.6 years. The initial models adjusted for age, season, and site found that subjects with lower 25(OH)D levels appeared to have higher odds of cognitive impairment than subjects with levels in the highest quartile (Q4). The lowest quartile (Q1) had 25(OH)D levels at or below 19.9 ng/mL. The OR for Q1 was 1.84, the OR for Q2 was 1.42, and the OR for Q3 was 1.18.

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