Low Vitamin D Among the Elderly Is Associated With Significant Decline in Cognition, Dementia
The researchers say their findings amplify the importance of identifying vitamin D insufficiency among the elderly, particularly high-risk groups such as blacks and Hispanics, who are less able to absorb the nutrient from its most plentiful source: sunshine. Among those groups and other darker-skinned individuals, low vitamin D should be considered a risk factor for dementia, they say.
The research is published online in JAMA Neurology, a JAMA Network journal.
"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," says Joshua Miller, a professor in the UC Davis department of pathology and laboratory medicine at the time when the research was conducted and now a professor and chair of the department of nutritional sciences at Rutgers University.
"This work, and that of others, suggests that there is enough evidence to recommend that people in their 60s and older discuss taking a daily vitamin D supplement with their physicians," Miller says. "Even if doing so proves to not be effective, there's still a very low health risk to doing it."
The large, longitudinal study was conducted in nearly 400 racially and ethnically diverse men and women in Northern California participating in longitudinal research at the Alzheimer's Disease Center in Sacramento, California. Fifty percent of participants were Caucasian and 50% were black or Hispanic. The participants had a mean age of 76 and were either cognitively normal, or had mild cognitive impairment or dementia.
The participants' serum vitamin D status was measured at the beginning of the study. Vitamin D deficiency and insufficiency were prevalent among all of the study participants. Overall, 26% were deficient and 35% were insufficient. Among Caucasians, 54% had low vitamin D, compared with 70% of blacks and Hispanics.
Over five years of follow-up, vitamin D deficient individuals experienced cognitive declines that were two to three times faster than those with adequate serum vitamin D levels. In other words, it took only two years for the deficient individuals to decline as much as their counterparts with adequate vitamin D declined during the five-year follow-up period.
"We expected to see declines in individuals with low vitamin D status," says Charles DeCarli, director of the Alzheimer's Disease Center. "What was unexpected was how profoundly and rapidly [low vitamin D] impacts cognition."
Exposing the skin to sunlight is the major source of vitamin D. Racial and some ethnic minorities are at greater risk of low vitamin D because the higher concentration of melanin that makes their skin darker—and protects against skin cancer in sunny climates—also inhibits synthesis of vitamin D.
Diet is the other major source of vitamin D. Dietary vitamin D is obtained particularly through dairy consumption. The intake of dairy products is especially low among minority groups, with only 6.5% of blacks and 11% of Mexican-Americans nationwide consuming the recommended three daily servings of dairy products, the study says.
"I don't know if replacement therapy would affect these cognitive trajectories. That needs to be researched and we are planning on doing that," DeCarli says. "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."
Source: UC Davis Health System