One study suggests that low blood levels of vitamin D may increase risk for cognitive decline, while another study shows that consuming a diet rich in the antioxidant powerhouse vitamin E may help reduce the risk for dementia, including Alzheimer's disease.
But experts, including the study researchers, caution that it is still too early to make any blanket recommendations about what individuals should eat and what supplements they should take to reduce their risks for age-related cognitive decline and dementia.
In the vitamin D study of 858 adults aged 65 and older, those with the lowest blood levels of vitamin D -- less than 25 nanomoles per liter of blood -- were 60% more likely to show signs of general cognitive decline during the six-year study and 31% more likely to show declines in their ability to plan, organize, and prioritize (so-called executive function), than their counterparts who had sufficient blood levels of vitamin D.
The findings appear in the July 12 issue of the Archives of Internal Medicine.
Vitamin D is often called the sunshine vitamin because our bodies produce it in response to sunlight. Vitamin D has become the "it" vitamin in recent years, as growing research links its deficiency to a host of health problems including heart disease, certain cancers, osteoporosis, diabetes, schizophrenia, and some autoimmune disorders.
Anywhere from 40% to 100% of older adults in the U.S. and Europe may be vitamin D-deficient, according to information cited in the new study.
Can Vitamin D Prevent Dementia?
"Our study demonstrates that low levels of vitamin D are associated with an increased risk of new cognitive problems," study researcher David J. Llewellyn, PhD, of the University of Exeter, England, says in an email. "This raises the possibility that vitamin D supplements may have therapeutic potential for the prevention of dementia and clinical trials are now urgently needed."
"We do not yet know the optimal intake of vitamin D to protect the brain as we need the results of clinical trials to confirm this," he says.
Andrew Grey, MD, of the University of Auckland in New Zealand, co-authored an editorial accompanying the new study that calls for rigorously designed trials. The new study "should serve as a springboard to conduct a randomized placebo-controlled trial to investigate whether vitamin D supplements prevent dementia," he says in an email.
"Similarly, other observational studies have reported associations between lower levels of vitamin D and many other diseases [and] randomized controlled trials of vitamin D supplementation are required to determine whether these associations are causal," he says.
As of right now, "vitamin D should only be measured if clinically indicated -- [such as in] the frail elderly, dark-skinned people -- and those who avoid the sun for religious, cultural, or medical reasons are at risk of clinically important vitamin D deficiency," he says.
"At present, there is not rigorous evidence for health benefits of vitamin D supplementation in community-dwelling individuals, beyond avoiding the very low levels," he says. The bottom line? "Routine supplementation of vitamin D is not, at present, justified."
Michael Holick, MD, PhD, is not as cautious in his interpretation of the new findings or in his vitamin D recommendations. As a professor of medicine, physiology, and biophysics at the Boston University School of Medicine and the director of the Vitamin D, Skin, and Bone Research Laboratory there, Holick has been warning Americans about the dangers of vitamin D deficiency for most of his career.
"I am not at all surprised that vitamin D deficiency is associated with cognitive decline," he tells WebMD. His advice is simple: "Take more vitamin D. All adults should consume 2,000 international units (IU) of vitamin D per day."
Currently, the dietary reference intake (DRI) for vitamin D is 200 IU per day for adults aged 14 to 50, 400 IU per day for adults 50 to 71, and 600 IU per day for those older than 71. The Institute of Medicine is considering new recommendations for vitamin D intake.
But the jury is in, according to Holick, and the time to supplement is before you develop signs of dementia or other diseases. "The role of vitamin D is to prevent and reduce risk of disease more so than treat them," he says.
Vitamin E and Alzheimer's Risk
A second study in the July issue of the Archives of Neurology shows that eating foods rich in vitamin E may help lower risks of developing dementia and Alzheimer's disease.
Vitamin E can be found in whole grains, wheat germ, leafy green vegetables, sardines, egg yolks, nuts and seeds, but most participants in the new study got their vitamin E from margarine, sunflower oil, butter, cooking fat, soybean oil, and mayonnaise. Antioxidants like vitamin E protect the body from damage caused by harmful molecules called free radicals.
In the study of 5,395 people aged 55 and older, those who got the most vitamin E in their diet -- 18.5 milligrams per day, on average -- were 25% less likely to develop dementia than their counterparts who got the least vitamin E on their diet, about 9 milligrams per day.
Elizabeth R. Devore ScD, of Erasmus Medical Center in Rotterdam, Netherlands, and colleagues followed the study participants for 9.6 years. During this time, 465 developed dementia, including 365 cases of Alzheimer's disease. They also looked at how much vitamin C, beta-carotene, and flavonoids participants consumed, but only dietary vitamin E seemed to be related to dementia risk.
More Study Needed
Mary Sano, PhD, the director of the Alzheimer Disease Research Center and a professor of psychiatry at the Mount Sinai School of Medicine in New York City, says that more study is needed before any recommendations can be made about vitamin D or vitamin E and dementia risk.
"There is no assurance that raising the levels of vitamin D would reduce the association with cognitive decline," she tells WebMD in an email. "This report should not lead us to vitamin supplementation for everyone, but if one's levels are severely low then supplementation may be warranted for many reasons, not just dementia."
As far as eating more vitamin E-rich foods to reduce risk of Alzheimer's disease, Sano says other factors may be at play; meaning that it may not be the E per se as much as the fact that people who eat diets that are rich in vitamin E and other antioxidants may eat less fat and sugar. She also cautions that the benefits were seen from whole foods, not supplements.
"The importance of this study is that it suggests that dietary factors, particularly shifting food intakes from one food group to perhaps a healthier one, may have benefit, but many of the supplementation studies have not shown that you can reverse the effects of diet by taking vitamins," she says.