Vitamin D Offers No Protection Against Alzheimer's
This was the conclusion that researchers in Australia came to, after conducting a systematic review and analysis of more than 70 clinical and pre-clinical studies.
But what was not clear from these, she and her colleagues note, is whether low vitamin D contributes to neurodegeneration or merely accompanies it.
Their analysis, says Iacopetta, contradicts â€œan emerging belief [â€¦] that higher levels of vitamin D can impact positively on brain health.â€
However, while they found no robust evidence of a â€œneuroprotectiveâ€ role for vitamin D, they did not rule out that the â€œsunshine vitaminâ€ might be a marker for some other protective factor.
They add that further studies are needed to identify a mechanism through which UV exposure might have this effect.
Neurodegenerative diseases are those that damage and kill nerve cells, or neurons, in the brain and other parts of the central nervous system. While they have this feature in common, their causes, symptoms, and how they progress can vary considerably.
Alzheimerâ€™s disease, for example, is a neurodegenerative disease that causes dementia and whose hallmarks include buildup of certain toxic proteins in the brain.
Another example is Parkinsonâ€™s, a disease that kills cells that produce dopamine, a chemical that the brain needs to control movement and other functions.
Multiple sclerosis (MS) is a disease that attacks the protective covering on the fibers that connect neurons to one another, causing breakdown in communication and, eventually, death of cells.
While Alzheimerâ€™s and Parkinsonâ€™s are more common in older people, MS tends to strike earlier in life.
Vitamin D, sunshine, and health
Our bodies make vitamin D when UV rays from the sun fall on exposed skin. It is also present naturally in certain foods and in fortified products.
For many people, these sources of vitamin D may suffice, but some groups may need to take supplements to meet their daily requirement.
Whether vitamin D comes from UV exposure, food, or dietary supplements, it has to undergo two chemical changes before the body can use it. One change takes place in the liver, and the other takes place mostly in the kidneys.
Vitamin D is important for health in several ways. It helps the body to make and maintain bones, regulate cell growth, control muscles, reduce inflammation, and modulate immune function.
In some of these roles, vitamin D interacts directly with genes that instruct cells how to make the proteins that control the various functions.
No â€˜causal roleâ€™ in neuroprotection
They concluded instead that â€œthe link between vitamin D and brain disorders is likely to be associative â€” as opposed to a directly causal relationship.â€
UV light may impact brain by other means
He explains that â€œsome early studiesâ€ have suggested that exposure to UV from the sun might have a â€œpositive impactâ€ on MS and similar neurological disorders.
Their findings allow for the possibility that â€œUV light may impact molecular processes in the brain in a manner that has absolutely nothing to do with vitamin D,â€ he adds.
A lot more research needs to be done before we can â€œfully understand whatâ€™s happening,â€ he concludes.
â€œWe could not establish a clear role for a neuroprotective benefit from vitamin D for any of the diseases we investigated.â€