Vitamin D used to be known simply for its important role of aiding in absorption of calcium, strengthening bones. Now, according to Dr. Amie Peterson of Oregon Health & Science University in Portland, vitamin D also seems to be anti-inflammatory, maintaining blood vessels, and feeding brain cells with healthy blood flow preventing cognitive impairment. It may even have a positive effect on brain tissue.
It would seem that vitamin D deficiency may cause cognitive impairment. Research has shown that low levels of vitamin D were linked with low scores on a test that indicated cognitive impairment.
"The average vitamin D level was 42.8 for the 42 participants with a perfect score of 30 on the test; 36.7 for the 89 participants who scored between 27 and 29 ('still normal but lower,' says Peterson), and 34.8 for the 21 people with scores of 22 to 26 ('mild cognitive impairment')."
Low levels of vitamin D were also linked with a higher risk of falling.
In another study women with levels below 10 nanograms per mililiter had vitamin D deficiency, and were twice as likely to have cognitive impairment as well.
http://www.webmd.com/healthy-aging/news/20100416/low-vitamin-d-level-tied-to-cognitive-decline?ecd=wnl_hbn_052410