Is vitamin D supplementation of potential benefit for community-living people with Alzheimer's disease?
Vitamin D is associated not only with effects on calcium and bone metabolisms but also with many chronic diseases. Low vitamin D levels in patients with Alzheimer's disease have been widely reported in the literature.
The purpose of this study was to critically review the potential benefit of vitamin D supplementation in individuals with Alzheimer's disease living in the community. Methods: A systematic literature search was conducted in PubMed, CINAHL, EMBASE and the Cochrane Library for papers published 2011–2018.
Seven papers were selected, consisting of one clinical trial, five cohort studies and one systematic review. Studies showed an association only between vitamin D deficiency and lower attention in older people. None of the reviewed studies provided evidence of a positive impact of vitamin D supplementation on cognitive function in older people with Alzheimer's disease.
There was no evidence that vitamin D supplementation has a direct benefit for Alzheimer's disease. The review synthesised the existing body of knowledge and concluded that optimum levels of vitamin D (neither too low nor too high) do appear to have positive effects on patient outcomes and quality of life. It is still unclear why vitamin D intake is inadequate as people age. Further research is needed to clarify vitamin-D-related aspects of Alzheimer's disease.
Chronic diseases not only threaten the quality of life but also impose a significant burden on the economy in terms of health expenditure (Ünal et al, 2013). These diseases are also seen to have slow progression and a long duration. Alzheimer's disease is an irreversible brain disorder that is slow progressing and leads to memory loss and deteriorating thinking skills over a long period of time (Leung et al, 2018). According to recent evidence, vitamin D is associated not only with its known effects on calcium and bone metabolism but also with many chronic diseases due to the widespread presence of vitamin D receptors in the body (Staud, 2005; Mpandzou et al, 2016; Veldurthy et al, 2016). In addition, inadequate vitamin D intake with ageing has been reported and vitamin D deficiency is presumed to be associated with Alzheimer's disease (Meehan and Penckofer, 2014). Vitamin D is sometimes referred to as the ‘sunshine vitamin’ since it is synthesised in humans when the skin is exposed to ultraviolet-B (UVB) light from the sun, as well as being obtained from dietary sources, and both routes are important in maintaining optimum levels (Nair and Maseeh, 2012). Reduced outdoor activities, skin wrinkles or poor skin integrity and malabsorption disorders with ageing are held responsible for low vitamin D in patients with Alzheimer's disease (Meehan and Penckofer, 2014).
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