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Hispanics and African Americans may also be at greater risk of vitamin D insufficiency, based on the study results.
Vitamin D has been found to promote bone health, calcium absorption, and the healthy function of many different organs, but vitamin D levels may also be linked to cognitive health as people age. Researchers are now suggesting that low levels of vitamin D may be associated with more rapid cognitive decline among older people, based on the results of a new study.
The study, published in JAMA Neurology, followed a multiethnic group of 382 adults with an average age of 75 years. The researchers measured vitamin D levels based on serum 25-hydroxyvitamin D (25-OHD) content in the blood and assessed cognitive function with the Spanish and English Neurophyschological Assessment Scales.
Upon comparing a baseline assessment with follow-up results taken an average of 4.8 years later, the researchers found 25-OHD levels were “lower in the dementia group compared with the mild cognitive impairment and cognitively normal group,” according to the study. The dementia group averaged 16.2 ng/mL 25-OHD levels, compared with 20.0 and 19.7 ng/mL levels for the mildly cognitive impaired and cognitively normal groups, respectively.
“About 60% of the group, regardless of their race or ethnicity, was low in vitamin D,” says Joshua W. Miller, PhD, one author of the study, in a press release from the Council for Responsible Nutrition (CRN; Washington, DC).
“Those low in vitamin D declined more in short term memory, known as episodic memory, as well as more complex cognitive tasks, known as executive function,” says Miller. “They were declining about two and a half times faster than those who had adequate vitamin D.”
Vitamin D status, however, did not seem to be associated with a decline in semantic memory or visuospatial ability, the researchers concluded. They added that it remains to be determined whether Vitamin D supplementation can actually slow cognitive decline.
The study also found that mean 25-OHD levels were significantly lower for African American and Hispanic participants compared with white participants: 17.9 ng/mL for African American participants, 17.2 ng/mL for Hispanic participants, and 21.7 ng/mL for white participants.
Vitamin D status was defined in the study as follows: less than 12 ng/mL for deficient, 12 to less than 20 ng/mL for insufficient, and 20 to less than 50 ng/mL for adequate. Among the group of 382 participants, 61.8% were women, 41.4% were white, 29.6% were African American, 25.1% were Hispanic, and 3.9% were of another race/ethnicity. Diagnosis at enrollment included 17.5% of participants with dementia, 32.7% with mild cognitive impairment, and 49.5% cognitively normal.
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Miller JW et al., “Vitamin D status and rates of cognitive decline in a multiethnic cohort of older adults,” JAMA Neurology. Published online September 14, 2015.