Spending more time in the sun to boost your vitamin D levels may help stave off the cognitive decline associated with aging, according to a study conducted by researchers from the University of Kentucky.
The study suggests that a vitamin D supplement helps accelerate the biological mechanisms responsible for recycling and renewing neurotransmitters (signaling chemicals) in an area of the brain that plays a key role in memory and learning. This leads to an improved ability of neurons to receive and process signals related to memory formation and retrieval.
"This process is like restocking shelves in grocery stores," researcher Nada Porter said.
Study confirms higher recommended doses
Scientists have long known that vitamin D plays a critical role in forming and maintaining healthy bones and teeth. In recent years, they have begun to learn that the vitamin is also essential to immune function, and that insufficient levels may increase the risk of cancer, autoimmune diseases and other health problems. Studies suggest that low vitamin D levels may also increase the risk of age-related cognitive decline.
In the new study, researchers placed rats on diets with either high, medium or low levels of vitamin D3. After six months, they tested the rats' ability to remember the location of a platform in a water maze. They then moved the platform, and tested the rats' ability to remember the new location.
"This was a more challenging task and, therefore, more sensitive to the subtle changes in memory that occur with aging," Porter said.
Rats who had been on the high-vitamin-D diet used shorter routes to reach the new platform than the other rats, and also reached it more quickly. The paths that they used tended to be relatively simple and consist of few direction changes. In contrast, the paths used by the low-dose rats resembled the loopy drawings made by kindergarteners.
The researchers also found that the rats on the high-dose diet showed changes in gene expression in the region of the brain known as the hippocampus, which is believed to play a central role in cognition and memory formation and consolidation. These rats' brains showed accelerated transport of neurotransmitters.
The vitamin D dose that produced improvements in rats was equivalent to a dose 50 percent higher than the Institute of Medicine's current daily recommendation for humans, which is based on the levels needed for bone health. The levels in the study are consistent, however, with the higher daily doses that many vitamin D experts are now recommending.
The researchers noted that the D3 form of vitamin D is associated with very few side effects.
Sunlight improves brain health
A number of prior studies have suggested a connection between vitamin D and cognitive decline. Some studies have shown that dementia patients have lower vitamin D levels than their healthy counterparts. A study in 2009 found that low vitamin D levels were associated with worse performance on tests of attention, memory and orientation in time and space.
Other studies have suggested that vitamin D can also lower the risk of Parkinson's disease, schizophrenia and even depression.
Although vitamin D can be found in certain foods (mainly those that are artificially fortified), the best source of the vitamin is ordinary sunlight. Light-skinned people can generate all the vitamin D their bodies need with about 15-30 minutes of unprotected sun exposure on their faces and hands daily; darker skin requires correspondingly longer exposure (up to twice as much).