Can vitamin D supplementation help with treatment or prevention of Alzheimer’s disease?

Numerous studies have been published suggesting that vitamin D may help to ameliorate some factors associated with the etiology of Alzheimer’s disease, prompting some scientists to suggest that it may be helpful for treating or preventing the disease.^[1] In support of this idea, Vitamin D treatment has been shown to have neuroprotective effects in in vivo animal studies, and human observational studies have found associations between low vitamin D levels and an increased risk of Alzheimer’s. Additionally, an in vitro study of immune cells cultured from the blood of people with Alzheimer’s found that treatment of these cells with vitamin D can increase their breakdown of amyloid-β protein aggregates, which accumulate in the brains of people with Alzheimer’s disease and may be associated with disease pathogenesis.^[2]

However, clinical randomized controlled trials (RCTs) are the only true test of whether or not any given supplement is useful to treat a disease, and the RCTs to date on vitamin D supplementation and Alzheimer’s have reported mixed results. Although one study found that 800 IU (20 μg) of vitamin D taken daily for 12 months significantly improved cognitive function in people with Alzheimer’s disease,^[3] many other trials of vitamin D supplementation in people with Alzheimer’s disease have not found significant effects.^[4] Although vitamin D deficiencies may increase Alzheimer’s disease risk, evidence for a therapeut