Background: 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. Aim: 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. Results: 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. Conclusion: 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.