Study Shows Low Vitamin D Levels Linked to Faster Cognitive Decline

16 Sep 2015 --- Low levels of vitamin D are associated with more rapid cognitive decline among older people, according to a new study released today1. Entitled “Vitamin D Status and Rates of Cognitive Decline in a Multiethnic Cohort of Older Adults,” the results appear online in the medical journal JAMA Neurology. The authors are Joshua W. Miller, Ph.D., of the Department of Nutritional Sciences at Rutgers University, New Brunswick, N.J., and his colleagues from the University of California, Davis.

We now know that vitamin D is essential for many organ functions in addition to ensuring strong bones by enhancing calcium absorption. There are many receptors for the fat soluble vitamin D throughout the brain and its active form has been shown to have widespread neuroprotective effects, including clearing amyloid plaques such as those found in Alzheimer’s disease. A study conducted in 2012 also showed a link between low levels of the active form of vitamin D and dementia throughout Europe and the US it has previously been unclear whether cognitive decline leads to low vitamin D levels via dietary changes at the onset of disease or whether it is low levels of this vitamin that contributes to dementia, but this research sheds some more light onto this question.

It has been proposed that vitamin D affects cognitive function via its influence on the growth and survival of neurons and by affecting neuronal apoptosis. In this latest study, the researchers wanted to see what effect vitamin D status has on the cognitive function of older adults of various ethnic backgrounds. In order to do this, they looked at the baseline levels of vitamin D in a multiethnic group of volunteers and compared those levels with their cognitive function. They also assessed how the change in cognitive function correlated with vitamin D status over time.

There were 382 older adults in the study; their average age was 75 years old. More than half (62%) were women. Although the largest number of participants were white, at 41%, 29.6% were African American and 25% were Hispanic. In terms of cognitive function, at the beginning of the study 49.5% of the participants were cognitively normal, 32.7% were mildly cognitively impaired, and 17.5% had dementia. The investigators measured vitamin D levels with blood (25-OHD).

At baseline, the investigators found that the average 25-OHD levels were lower for the African American (17.9 ng/mL) and Hispanic participants (17.2 ng/mL) when they were compared with the white subjects (21.7 ng/mL). They also noted that average 25-OHD levels were lower in the dementia group than in the mildly cognitive impaired and cognitively normal groups (16.2, 20.0 and 19.7 ng/mL, respectively). On follow-up, which averaged 4.8 years, the researchers found that subjects who had deficient (less than 12 ng/mL) or insufficient (12 to less than 20 ng/mL) vitamin D status had the greatest rates of cognitive decline.

Dr. Miller explained in the audio portion of the news release, “About 60% of the group, regardless of their race or ethnicity, was low in vitamin D. Those low in vitamin D declined more in short term memory, known as episodic memory, as well as more complex cognitive tasks, known as executive function. They were declining about two and a half times faster than those who had adequate vitamin D.”

The researchers call for more studies to determine whether vitamin D supplements can slow cognitive decline. Dr Miller says, “we are very much in need of randomized control trials to determine if vitamin D supplements are superior to placebo in slowing cognitive decline or delaying or preventing Alzheimer's Disease or dementia in older adults. No such trials have been published as of yet.”