Pair of Studies Link Vitamin D, Cognitive Ability in Seniors

Two recent studies indicate that vitamin D intake can have a significant effect on the cognitive abilities of the elderly.

Unfortunately, more than half of older Americans have insufficient levels of vitamin D, according to David Llewellyn, Ph.D., a researcher at the University of Exeter Peninsula Medical School, United Kingdom.

Llewellyn presented data on this topic from the Third National Health and Nutrition Examination Survey, or NHANES III, during the Alzheimer's Association International Conference on Alzheimer's Disease 2010, July 10-15 in Honolulu.

Researchers examined information from more than 3,000 adults ages 65 and older who participated in NHANES III. Vitamin D levels in blood samples were assessed in relation to participants' performance on cognitive function tests for memory, orientation in time and space, and attention span.

According to Llewellyn, 8 percent of the subjects who had sufficient levels of vitamin D were cognitively impaired compared with 15 percent of subjects who were vitamin D-insufficient and who demonstrated cognitive impairment. Those who had significant vitamin D insufficiencies were four times more likely to be impaired.

"The lower your vitamin D level, the more likely you are to have cognitive impairment," he said.

Llewellyn said many older Americans aren't exposed to enough sunlight to produce adequate levels of vitamin D, and skin becomes less efficient at producing the vitamin as the body ages. He also said there are few dietary sources with high levels of naturally occurring vitamin D and noted that even foods that are fortified with the vitamin still do not provide adequate levels.

According to Llewellyn, vitamin D may protect blood flow to the brain and also may clear toxins from the brain, including the amyloid proteins associated with Alzheimer's disease. But, he added, more research is needed to establish whether vitamin D supplementation has therapeutic potential for dementia.

"We used to think vitamin D was just important for bone health," Llewellyn said during his presentation, "but we actually now know that vitamin D seems to play a role in a much wider range of age-associated diseases, and they're the ones we worry about -- like cancer, high blood pressure, heart disease, stroke and so on."

Llewellyn also is the lead author of a similar study recently published in the Archives of Internal Medicine.

In that study, sufficient levels of serum 25-hydroxyvitamin D (25[OH]D) were defined as 75 nanomoles per liter or greater, while severe insufficiency was defined as 25 nmol/L or less.

Researchers used data from more than 800 noninstitutionalized Italians ages 65 and older who were enrolled in the InCHIANTI (Invecchiare in Chianti, or "aging in the Chianti area") study. Blood test results were assessed in relation to the results of three cognitive evaluations -- the Mini-Mental State Examination and Trail Making Test Parts A and B.

Scores for all three tests were significantly lower in subjects who were vitamin D-deficient or severely deficient than in those who had sufficient levels, and more than half of participants with dementia were severely vitamin D-deficient.