"There were some people in the study who had low vitamin D who didn't decline at all and some people with adequate vitamin D who declined quickly," says Joshua Miller. "But on average, people with low vitamin D declined two to three times as fast as those with adequate vitamin D." (Credit: iStockphoto)

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Low vitamin D speeds up cognitive decline

Older adults who don’t get enough vitamin D may experience cognitive decline at a much faster rate than people who have adequate vitamin D, a new study suggests.

We obtain vitamin D—known for its importance for bone health—primarily through sun exposure and some foods. It also has a major impact on how the body, including the brain, functions.

The study assessed 382 people with normal cognition, mild cognitive loss, or dementia once a year for an average of five years.

Unlike previous studies of vitamin D and dementia, the participants were racially and ethnically diverse and included whites, African Americans, and Hispanics. Most (61 percent) had low vitamin D levels in their blood, including 54 percent of the whites and 70 percent of the African-Americans and Hispanics. Participants ranged in age from their 60s to their 90s, with the largest group in their 70s.

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“There were some people in the study who had low vitamin D who didn’t decline at all and some people with adequate vitamin D who declined quickly,” says Joshua Miller, professor of nutritional science at Rutgers. “But on average, people with low vitamin D declined two to three times as fast as those with adequate vitamin D.”

While individuals with darker skin are more likely to have low levels of vitamin D because melanin, the pigment that makes skin dark, blocks the ultra-violet rays that help the skin synthesize vitamin D, there was no difference in the rates of cognitive decline based solely on racial or ethnic lines.  In other words, low vitamin D was associated with faster cognitive decline regardless of race or ethnicity.

Although taking too much vitamin D can be dangerous, the findings, published in JAMA Neurology, suggest that people over 60 should consult their physician about taking vitamin D supplements.

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“Some people may have had melanoma or fear getting it,” Miller says. “Or, they may live in climates where the sun isn’t powerful enough, or do work that keeps them out of the sun. That’s where supplements come in.”

Meanwhile, more research needs to be done including performing randomized controlled clinical trials, Miller says. “This will give us the additional information that we need to help determine whether vitamin D supplements can be used to slow the rate of cognitive decline and prevent dementia in older adults.”

Miller conducted the research between 2002 and 2010 at the Alzheimer’s Disease Center at the University of California, Davis, with  Charles DeCarli, Danielle Harvey and others.

Source: Rutgers

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