October 20, 2010
Vitamin D, the so-called “sunshine vitamin” long linked to healthy bones, has also been hailed as a possible protector against heart disease, diabetes and obesity. Now, a new study from Italy finds that the vitamin may be important for brain health and preventing the memory decline of Alzheimer’s disease.
The study, published in the Archives of Internal Medicine, involved 858 men and women ages 65 years and older. In the six-year study, those with the lowest blood levels of vitamin D were most at risk of memory, learning and thinking problems.
It is estimated that well over half of older adults in the United States and Europe are thought to be deficient in vitamin D, the researchers report, with some estimating that virtually all seniors are deficient in the vitamin. The body makes vitamin D in the skin on exposure to the sun. But seniors tend to get less sun exposure than younger people, and the body’s ability to produce vitamin D declines with age.
Other researchers have provided convincing evidence that vitamin D supplementation can lower the risk of developing Alzheimer’s disease in people who suffer from vitamin D deficiency but not in people who have adequate levels of vitamin D in their body.
Vitamin D may play a role in the formation of nerve cells, including tissue in the brain. The nutrient may also aid the brain by maintaining levels of calcium, a mineral critical for sending signals from one nerve cell to the next, and by helping to rid the brain of beta-amyloid, which in excess forms the brain plaques of Alzheimer’s disease.
The researchers, from the University of Exeter in England, assessed blood levels of vitamin D at the start of the study, then again after three and six years. Participants were also given regular tests of memory, attention, planning and thinking skills.
Compared to those with normal vitamin D levels, seniors with the lowest levels of 25-hydroxyvitamin D, a form of the vitamin that circulates in the blood (they had levels of less than 25 nanomoles per liter of blood), were 60 percent more likely to have substantial memory and thinking decline over the six-year study period. They also were 31 percent more likely to experience declines on tests measuring executive function, or the ability to plan and execute tasks.
“If future prospective studies and randomized controlled trials confirm that vitamin D deficiency is causally related to cognitive decline, then this would open up important new possibilities for treatment and prevention,” the authors concluded.
“Very importantly, such trials will also provide an opportunity to systematically assess potential harms of vitamin D supplementation, an issue that has been largely overlooked or dismissed,” wrote doctors from the University of Auckland in New Zealand, in an editorial accompanying the study.
Vitamin D is found naturally in some foods like fish, but you would have to eat a 3.5 ounce portion of salmon daily to get the recommended 600 IUs of the vitamin. Vitamin D is also added to milk, but it would take a daily quart to get the recommended dose. Spending 15 minutes or so in the sun each day, without sunscreens is sufficient to stimulate the skin to to produce adequate levels of the vitamin. But because of skin cancer risk, excessive sun exposure is not generally recommended.
Some doctors are recommending higher daily doses of 2,000 IUs or more as supplements, but the long-term effects of such high amounts are unknown. Vitamin D is fat soluble and remains in the body, stored in fat. Side effects of taking excessively high doses of vitamin D supplements can include digestive problems, headache, irregular heartbeats and extreme fatigue.
More study is needed to determine the role of vitamin D in brain health and Alzheimer’s prevention.
David J. Llewellyn, Ph.D., Iaian A. Lang, Ph.D., Kenneth M. Langa, M.D., Ph.D. et al: “Vitamin D and Risk of Cognitive Decline in Elderly Persons.” Archives of Internal Medicine, Vol. 170 (No. 13), July 12, 2010, pages 1135-1141.
Andrew Grey, M.D., Mark Bolland, MBChC, Ph.D.: “Vitamin D: A Place in the Sun?” Archives of Internal Medicine, Vol. 170 (No. 13) July 12, 2010, page 1099.