Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines

Vitamin D offers a wide range of under-recognized health benefits beyond its well-established role in musculoskeletal health. It plays a crucial role in extra-renal and skeletal tissues, prenatal and newborn health, brain health, immune function, cancer prevention, cardiovascular disease, etc. Current clinical guidelines, particularly the Endocrine Society's 2024 recommendations, remain limited in scope and have not addressed the vital extra-skeletal benefits of this vitamin nor the thresholds for vitamin D assays. Their recommendations were based on conclusions from randomized controlled trials of the benefits of vitamin D, which were infrequently found. Most such trials included participants with above average 25-hydroxyvitamin D [25(OH)D] concentrations and treated with low vitamin D doses and analyzed based on intention to treat. This review considers the role of vitamin D in reducing the risk of incidence and death for eight of the top ten causes of death in the US illustrating that serum concentrations above 30 ng/mL (75 nmol/L) compared to <20 ng/mL are associated with significantly reduced risk of incidence and mortality rates for many health outcomes. Since about a quarter of the US population and 60% in Central Europe have 25(OH)D concentrations <20 ng/mL, significant reductions in disease rates and deaths could be achieved by raising those values above the minimum of 30 ng/mL. Daily vitamin D supplementation with 2000 international units (IU) (50 µg) of vitamin D3 is recommended for prevention of vitamin D deficiency/insufficiency (i.e, serum 25(OH)D < 30 ng/mL)—sufficient for musculoskeletal system functions. However, intake above 4000 IU/day are recommended to raise serum 25(OH)D to the range 40‒70 ng/mL to achieve protection against many adverse health outcomes. This review aims to pave the way for more inclusive, evidence-based guidelines that enhance public health and personalized care.