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Vitamin D

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Vitamin D is an essential nutrient produced by the body and also found in fatty fish, fish oils, meats, and fortified milk and juice sold in the US. Vitamin D crosses the blood-brain-barrier both by passive diffusion, as well as active transport by cell-surface proteins. Additionally, the brain can synthesize its own vitamin D, as two of the primary enzymes needed (24-hydroxylase and 1α-hydroxylase) are expressed in the brain.

Vitamin D in the Brain

Vitamin D is an essential nutrient produced by the body and also found in fatty fish, fish oils, meats, and fortified milk and juice sold in the US. Vitamin D crosses the blood-brain-barrier both by passive diffusion, as well as active transport by cell-surface proteins. Additionally, the brain can synthesize its own vitamin D, as two of the primary enzymes needed (24-hydroxylase and 1α-hydroxylase) are expressed in the brain.

VitaminD SynthesisVitamin D biosynthesis

Vitamin D receptors (proteins that bind vitamin D and carry out its cellular effects), are located widely throughout the brain. In particular, in the orbital, temporal, and cingulate cortices, as well as the thalamus, nucleus accumbens, stria terminalis, and the amygdala.

Vitamin D has been shown to regulate the synthesis of neurotrophins and neurotransmitters – molecules that regulate growth and signaling, respectively. In particular, vitamin D has been shown to increase the synthesis of nerve growth factor, glial cell line-derived neurotrophic factor, and neurotrophin 3. Moreover, vitamin D has also been shown to be involved in regulating the synthesis of acetylcholine, dopamine, serotonin, and gaba. Thus vitamin D is involved in a huge variety of neural processes at the molecular level.

Vitamin D and Cognition

There is interesting data linking higher Vitamin D levels to reduced cognitive decline in older adults. However, there is little positive data linking vitamin D supplementation to improved cognitive performance in young, healthy adults.

In older individuals, low levels of vitamin D appear to affect executive brain functions, such as the processing of information, working memory, and multitasking. In addition, a recent meta-analysis showed there is a 2.4X greater risk of cognitive impairment in older adults with low levels of Vitamin D. Normal levels of vitamin D in the blood are between 20-50 nanograms per milliliter of blood.

There is not much data linking vitamin D levels to improved cognitive performance in young, healthy adults. In a 2011 placebo-controlled randomized control trial, vitamin D supplementation in healthy-young adults did not result in improvements in cognitive performance or mood states. However, in a study of young adults in the US, it was seen that low vitamin D levels were correlated with depressed mood. Thus, it is possible that individuals with normal levels of vitamin D do no benefit from supplementation, while those with lower levels may still benefit. Indeed, a 2002 cross-sectional study demonstrated that low vitamin D levels can also be seen in young, healthy individuals. In particular, vitamin D levels are at their lowest in the winter, when there is not a great deal of sunlight, which is critical for the production of vitamin D.

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