Vitamin D has increasingly become the focus of several scientific investigations as researchers seek to better understand the role that the compound plays in organ function, especially that of the brain. Now, new research indicates that vitamin D insufficiency may be associated with faster decline of cognitive function.
While the results could have implications for further research on dementia and other neurodegenerative diseases, it is still not known whether vitamin D supplementation will slow cognitive decline.
The study, led by Joshua W. Miller, PhD, of Rutgers University, and colleagues included an ethnically diverse group of 382 older adults, from which baseline serum 25-hydroxyvitamin D (25-OHD) status, and change in subdomains of cognitive function were collected. The average age of study participants was 75.5 years, 61.8% were female, and 41.4% were white, 29.6% were African American, 25.1% were Hispanic, and 3.9% were of another race or ethnicity. At enrollment, 17.5% had dementia, 32.7% had mild cognitive impairment, and 49.5% were cognitively normal.
Among all participants, the average 25-OHD level was 19.2 ng/mL, with 26.2% of participants being vitamin D deficient and 35.1% vitamin D insufficient. Average 25-OHD levels were lower in African American and Hispanic participants compared to white participants (17.9, 17.2 and 21.7 ng/mL, respectively). Those with dementia had lower 25-OHD levels than those with mild cognitive impairment and normal cognitive function (16.2, 20.0 and 19.7 ng/mL, respectively).
Compared to those with adequate vitamin D levels, those with deficient or insufficient levels experienced a greater rate of decline in episodic memory and executive function over a 4.8-year follow-up. However, vitamin D status was not significantly associated with declines in semantic memory or visuospacial ability.
“Independent of race or ethnicity, baseline cognitive ability, and a host of other risk factors, vitamin D insufficiency was associated with significantly faster declines in both episodic memory and executive function performance, which may correspond to elevated risk for incident AD [Alzheimer’s disease] dementia,” the authors wrote. “Given that vitamin D insufficiency is medically correctable, well-designed clinical trials that emphasize enrollment of individuals of nonwhite race/ethnicity with hypovitaminosis D could be useful for testing the effect of vitamin D replacement on dementia prevention.”