From Medscape Medical News

Low Vitamin D Levels Associated With Increased Risk for Cognitive Impairment

Susan Jeffrey

Authors and Disclosures

Other Health Care Provider Rating: ( 1 Vote ) Rate This Article:

July 13, 2010 (Honolulu, Hawaii) — Results of a new analysis using data from the Third National Health and Nutrition Survey (NHANES III) show that vitamin D deficiency is associated with an increased risk for cognitive impairment in older Americans.

The findings echo those from a second report from the same group in a different cohort showing that low levels of vitamin D were associated with subsequent cognitive decline during 6 years of follow-up.

Taken together, it appears that, "low levels of vitamin D are just genuinely bad for the brain," lead author David J. Llewellyn, PhD, from the University of Exeter Peninsula Medical School in the United Kingdom, told Medscape Medical News. "That's why we're so excited, because vitamin D supplements are such an obvious thing that we can do something about now."

Dr. David J. Llewellyn

The expected epidemic of dementia with the aging population is already starting to appear, he said, and although long-term strategies are needed, trials that may have a short- to medium-term payoff are urgently required immediately. In that setting, trials of vitamin D for prevention may be a promising strategy, he said.

The results from NHANES III were presented here at the Alzheimer's Association International Conference on Alzheimer's Disease 2010. The results from the Invecchiare in Chianti (InCHIANTI) study appear in the July 12 issue of the Archives of Internal Medicine.

NHANES Findings

Vitamin D was once just of interest in bone health, but recent work has suggested low vitamin D levels may be a risk factor for a wide range of age-associated diseases, Dr. Llewellyn said, including cancer, hypertension, stroke, and more recently, cognitive decline.

It is known that vitamin D crosses the blood–brain barrier and that receptors for vitamin D are found across the brain, but its precise role is still not known, Dr. Llewellyn noted. It does seem to play a role in processes that may be important for dementia risk, including vascular health and amyloid clearance from the brain. Given these associations, he noted, it seems "biologically plausible" that there might be an association of low vitamin D levels with dementia risk and cognitive performance in the general population.

It is estimated that about a billion people worldwide have vitamin D levels considered insufficient (<75>

A previous paper using data from NHANES III did not find an association between vitamin D levels and cognitive performance (McGrath J, et al. Neuroepidemiol. 2007;29:49-54), but the researchers speculated this may have related to methodology — specifically, the choice of cognitive tests included.

The previous paper used only delayed verbal memory from the Mini-Mental State Examination (MMSE) and the East Boston Memory Test, Dr. Llewellyn said. "I threw everything in, because I was interested in whether this would be a more stable representation of these individuals' cognitive status."

The researchers also adjusted for a wide range of variables, including vitamin E levels, family income, more extensive measures of physical activity, and obesity.

A total of 3325 adults aged 65 years or older had complete cognitive assessments and blood samples available; cognitive impairment was defined as the worst 10% of the distribution of combined scores. Vitamin D levels were divided by cut points previously established for bone health, from severely deficient (<25>

Compared with those patients with sufficient levels of vitamin D, those participants who were very vitamin D deficient had a 6-fold higher risk for cognitive impairment, with a doubling of risk still for those who were considered deficient (≥25 to <50>

"We see some attenuation in the fully adjusted model, but this is still a relatively large effect size, I think it's fair to say," Dr. Llewellyn noted. "People [with severe vitamin D deficiency] have about 4 times higher odds of cognitive impairment, and again the trend across groups remains significant."