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Low vitamin D levels a dementia risk factor for darker-skinned individuals

October 26, 2015
by Nicole Stempak, Assoicate Editor
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Low vitamin D levels among the elderly is associated with accelerated cognitive decline and impaired performance, according to a study published online in JAMA Neurology.  Researchers went so far as to say that for darker-skinned individuals, low vitamin D levels should be considered a risk factor for dementia.

Vitamin D deficient individuals experienced cognitive declines two-to-three times faster than those with adequate serum vitamin D levels, according to researchers from from the University of California Davis Alzheimer’s Disease Center and Rutgers University. In other words, it took only two years for the deficient individuals to decline as much as their counterparts with adequate vitamin D declined over the same time.

“Independent of race or ethnicity, baseline cognitive abilities and a host of other risk factors, vitamin D insufficiency was associated with significantly faster declines in both episodic memory and executive function performance,” said lead author Joshua Miller, PhD, in a news release. Miller was professor in the UCD department of pathology and laboratory medicine at the time when the research was conducted and is now professor and chair of the department of nutritional sciences at Rutgers University. Vitamin D levels were not significantly associated with a decline in semantic memory or visuospatial ability.

Researchers studied 382 people in Northern California who were participating in longitudinal research at the Alzheimer’s Disease Center in Sacramento, Calif. Forty-one percent of participants identified as white and 55 percent identified as black or Hispanic. Participants had a mean age of about 75 and were either cognitively normal or had mild cognitive impairment or dementia.

Participants’ serum vitamin D status was measured over the course of five years. Vitamin D deficiency and insufficiency were prevalent among all participants. Among whites, 65 percent had low vitamin D compared with 70 percent of blacks and Hispanics.

“We expected to see declines in individuals with low vitamin D status,” said Charles DeCarli, MD and director of the Alzheimer’s Disease Center. “What was unexpected was how profoundly and rapidly (low vitamin D) impacts cognition. This is a vitamin deficiency that could easily be treated and that has other health consequences. We need to start talking about it. And we need to start talking about it, particularly for people of color, for whom vitamin D deficiency appears to present an even greater risk.”

Sunlight is the primary source of vitamin D. People with darker skin tones typically have lower vitamin D levels because the higher concentration of melanin  that makes their skin darker also inhibits synthesis of vitamin D. The other main source of vitamin D is through dietary consumption primarily through dairy. Diary intake was found to be  especially low among minority groups, with only 6.5 percent of African-Americans and 11 percent of Mexican-Americans nationwide consuming the recommended three daily servings of dairy products, the study says.

Access the full study here.

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