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.

Related arti­cles on the rela­tion­ship between vit­a­mins and other sup­ple­ments and cog­ni­tive decline and/or dementia:

• Vit­a­min B against Alzheimer’s? Too early to tell.

• No effects of omega-3 sup­ple­ments on Alzheimer’s symptoms

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