Background: Vitamin D is a fat-soluble vitamin available from food and sun exposure. Vitamin D receptors are present in cells throughout the body and cause it to act like a hormone. Observational studies document the association of low vitamin D levels with multiple health conditions. This article reviews the evidence for vitamin D in prevention and treatment in primary care.Methods: We performed a literature review of randomized controlled trials, meta-analyses, systematic reviews, and large prospective trials looking at the role of vitamin D deficiency in the most common conditions seen in primary care and the top 10 causes of mortality since 2010.Results: Vitamin D supplementation in patients with known cardiovascular disease does not reduce risk of stroke or heart attack. Vitamin D supplementation does not seem to have an effect in the treatment of hypertension or in cancer prevention. There is emerging evidence that supplementation reduces COVID-19 severity and risk of mechanical ventilation. Vitamin D at more moderate levels may reduce the risk of falls, but higher doses may cause increased fall risk. There does not seem to be a link between vitamin D supplementation and improved cognition. Vitamin D supplementation may be helpful in patients with major depression. High dose vitamin D may improve pain in people with fibromyalgia. Supplementing patients with prediabetes reduced the risk of progression to type 2 diabetes mellitus. Vitamin D supplementation in addition to standard emollient treatment helped to reduce symptoms in people with atopic dermatitis.Conclusion: Prospective studies of vitamin D supplementation demonstrate variable impact on disease specific and patient-oriented outcomes, suggesting a correlation but not a causal relationship between low vitamin D levels and disease pathogenicity. Future research should determine dosing standards and timing of vitamin D in treatment and prevention.