November 2, 2015
Low levels of vitamin D may play a role in memory problems and the onset of Alzheimer’s disease and other forms of dementia in the elderly, according to a new report. The findings underscore the importance of identifying vitamin D deficiency in older men and women, say the researchers, from the University of California, Davis, and Rutgers University.
The researchers found that memory skills declined two to three times faster in those with low blood levels of the vitamin compared to those with adequate vitamin D levels. “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,” said study author Joshua Miller, now at Rutgers.
For the study, the researchers followed 382 men and women living in northern California for about five years. Their mean age was 75. Some had dementia or mild cognitive impairment, a serious form of memory loss that may eventually lead to a diagnosis of Alzheimer’s disease.
The researchers found that about 60 percent of the study participants were low in vitamin D. A healthy vitamin D level is general defined as about 20 to 25 nanograms of the vitamin per milliliter of blood.
Seniors who had low levels of vitamin D tended to score worse on tests of episodic memory, which is the ability to recall personal experiences that occurred at a particular time and place. They also performed worse on tests of executive function, or the ability to plan ahead and solve problems. Both aspects of memory are severely impaired by Alzheimer’s disease.
They also found that seniors in the study who had dementia had lower vitamin D levels than those with mild cognitive impairment or normal cognitive function.
The authors didn’t study whether vitamin D supplements might slow the rate of cognitive decline. But they plan to continue research to see if taking vitamin D supplements might slow or prevent the onset of Alzheimer’s or dementia in those getting supplements of the vitamin. “Even if doing so proves to not be effective, there’s still very low health risk to doing it,” Dr. Miller said.
Vitamin D, which promotes bone health, is sometimes called the sunshine vitamin because it is produced in the skin upon exposure to sunlight. People living in northern latitudes may be particularly prone to vitamin D deficiency during the winter months, when sunlight levels are low.
Certain ethnic groups are also particularly prone to vitamin D deficiency, including African-Americans and Hispanics, who are less able to absorb sunlight through the skin. Among those groups and other darker-skinned individuals, low vitamin D should be considered a risk factor for dementia, the authors note. The findings were published in JAMA Neurology, a journal from of the American Medical Association.
“This is a vitamin deficiency that could easily be treated and that has other health consequences,” said Charles DeCarli, a study author and the director of the Alzheimer’s Disease Center at UC Davis. “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,” he said.
Vitamin D is found naturally in some foods like fish, and it is also added to foods like milk. But the best way to raise blood levels of the vitamin is to spend at least 15 minutes in the sun each day.
Some doctors recommend taking vitamin D supplements, but the effects of taking very high doses are unknown. Vitamin D remains in the body, stored in fat, and getting excessive doses can produce side effects that can include digestive problems, headaches, irregular heartbeats and extreme fatigue.
Source: Joshua W. Miller, PhD; Danielle J. Harvey, PhD; Laurel A. Beckett, PhD; et al: “Vitamin D Status and Rates of Cognitive Decline in a Multiethnic Cohort of Older Adults.” JAMA Neurology, Sept. 14, 2015