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Identifying New Avenues of Research
New Critical Review by CHORI Scientists Joyce McCann, PhD and Bruce Ames, PhD Points to the Importance of Vitamin D in Brain Function

"The first two years of life are a very active and critical period in brain development, and as we discuss in these reviews, there is evidence of a negative impact on brain development if nutrition isn't adequate."

CHORI scientists Joyce McCann, PhD and Bruce Ames, PhD in the Center for Nutrition and Metabolism have just had a critical review on vitamin D and the brain published online by the Federation of American Societies for Experimental Biology Journal (FASEB J.), which will appear in print in the April 2008 issue of FASEB J.

“This critical analysis of vitamin D function and the brain is a model of careful thinking about nutrition and behavior,” says Gerald Weissmann, MD, Editor-in-Chief of FASEB J. “Drs. McCann and Ames deftly show that while vitamin D has an important role in the development and function of the brain, its exact effects on behavior remain unclear.”

The publication is the fourth in a series of reviews, intended for a broad scientific audience, that bring together evidence from multidisciplinary fields to examine effects of micronutrient deficiencies on fetal and postnatal brain development, which occurs during the first 2 years of life.

"This is the period during which trillions of neurosynapses - connections between neurons - are made, and also the period when myelin is formed, an insulating coating on nerve fibers that is essential for efficient nerve conduction," explains Dr. McCann.

The reviews, on the omega-3 fatty acid docosahexaenoic acid (DHA), choline, iron, and now vitamin D, explore whether evidence supports a causal relationship between deficiency and consequences for cognition or behavior later in life.

In the current review, Drs. McCann and Ames conclude that while there is a large body of evidence that strongly implicates vitamin D's involvement in critical functions in the brain, there is not yet definitive evidence to causally link vitamin D deficiency to observable deficits in cognitive function or behavior.

"An important piece of evidence linking vitamin D to brain function is that vitamin D receptors, the primary means by which vitamin D acts, are found in many areas of the brain, during development and throughout adult life," Dr. McCann says. "Also, the expression of a number of genes whose products are known to be involved in critical brain functions, such as neurotransmission, is influenced by vitamin D as well."

Nevertheless, studies in humans and animals that have attempted to directly measure changes in cognition or behavior under conditions of vitamin D inadequacy are not definitive.

As Dr. McCann explains, "Much of this evidence is either weak or inconsistent. We're not sure why this is, but one possibility has to do with the fact that most cognitive/behavioral studies were done using rodents, who are not exposed to much sunlight because they are covered with fur and mostly nocturnal. Rodents, unlike humans, may have back-up, or homeostatic, mechanisms that protect vital organs such as the brain from loss of vitamin D-regulated functions."

Despite the need for more research, however, the authors believe there is enough evidence to suggest that vitamin D supplementation, especially in at-risk populations, is a good idea.
"The question for public health is what this research means for people's behavior - should they take a vitamin D supplement or not?"
Since there are few natural food sources of vitamin D, supplementation is already recommended for at risk groups in order to protect against rickets, bone fractures, and possibly some forms of cancer. These groups include nursing infants, the elderly - whose skin loses the ability to make vitamin D with age, and people with dark skin, such as African Americans, whose skin is 6 times less efficient in making vitamin D than Caucasian skin.

"The bottom line is that while we can't say for sure based on the current evidence that if you are low in vitamin D there's going to be something wrong with your cognitive abilities or behavior, it still makes sense to take a supplement if you believe you may be low in vitamin D," says Dr. McCann.

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Tuesday, May 17, 2011 8:19 AM

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