The role of vitamin D in the brain appeared evident in the 1980s when researchers found key proteins in the brain involved in vitamin D metabolism. A lot of clinical evidence has accumulated since then suggesting that low vitamin D levels may potentially result in cognitive decline. Nonetheless the results are mixed and not all previous studies have show that low levels of vitamin D are indeed associated with cognitive decline or dementia.
A 2010 study evaluated this question for the first time by following the same individuals over the years, instead of comparing people with normal levels and people with low-levels of vitamin D. This study followed 858 adults 65 years and older over 6‑years. Results showed an increased risk of cognitive decline in patients with vitamin D deficiency.
Comments: An association between two things (here vitamin D levels and cognitive decline) does not necessarily means that one causes the other. Potential confounding factors may explain the association. For instance vitamin D deficiency has also been associated with cardiovascular disease, which is known to be a risk factor for dementia. However this recent study addressed such confounding factors and found that the relation between vitamin D deficiency and cognitive decline was maintained.
One question left to answer is whether vitamin D deficiency is part of the early manifestations of cognitive decline or whether it is risk factor that can be manipulated and acted upon. Whether taking vitamin D may help fight against cognitive decline is still unclear. In fact most of the evidence shows lack of benefits from a wide variety of typical supplements, from gingko to vitamins.
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