Vitamin D May Protect Against Cognitive Decline

Getting out in the sunlight may be the best thing for this couple's mental functioning. Credit: Ruslan Guzov/Shutterstock

People aged over 60 with vitamin D deficiencies are more prone to losing brain power, according to a new study. While the cause of the relationship remains unclear, it adds to a growing body of research indicating insufficient vitamin D could be harmful in a remarkably diverse number of ways.

Between 2002 and 2010 Rutgers University’s Professor Joshua Miller and his colleagues measured vitamin D levels and cognitive performance of 382 people annually. They ranged in age from their 60s to their 90s, with those in their 70s making up the largest group. The study was inspired by observations that low vitamin D is more common in Alzheimer's sufferers, although previous studies finding this correlation have not shed light on the direction of causation.

Almost half the subjects were “cognitively normal” at enrollment, around a third had mild cognitive impairment and 17.5% had been diagnosed with dementia. A disturbing 61% had low vitamin D levels for at least part of the study, with the proportion even higher among African Americans and Hispanics at 70%. This difference was expected – melanin, the pigment that makes skin darker, blocks ultraviolet rays that help the skin synthesize vitamin D – but as previous studies have largely focussed on white populations, this research offers a more complete picture of the relationship between vitamin D and cognitive decline.

The results were published in the Journal of the American Medical Association – Neurology. "There were some people in the study who had low vitamin D who didn't decline at all and some people with adequate vitamin D who declined quickly. But on average, people with low vitamin D declined two to three times as fast as those with adequate vitamin D," said Miller in a statement. The authors note in the paper that: “The rate of cognitive decline associated with hypovitaminosis D (insufficiency and deficiency) was greatest for episodic memory and executive function.” No differences in the rate of decline were found between ethic groups.

Although diets contribute, most people produce the bulk of the closely related chemicals collectively known as vitamin D from casual exposure of their skin to UV radiation.

The importance of vitamin D for bone health has been known for almost a century. However, despite public health campaigns urging older people to take supplements if they are not spending much time in the sun, our indoor lifestyles are causing an epidemic of low vitamin D, particularly at high latitudes.

Meanwhile a procession of papers have indicated the consequences could go far beyond brittle bones. Deficiencies have been connected to everything from increased cancer risk to depression. Insufficient vitamin D maybe a problem early in life as well, with deficiencies before and after birth linked to schizophrenia in adulthood.

These findings remain disputed, and even the researchers responsible debate whether the vitamin D intake required for bone health is sufficient for other purposes. Nevertheless this study contributes to suggestions that tackling vitamin D deficiency could be one of the most important public health challenges facing many countries, particularly those far from the equator.

Excessive vitamin D levels can also have negative consequences, but is a far less common problem. Nevertheless, Miller recommends people over 60 consult their doctor about getting vitamin D supplements, rather than self-medicating.

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