Vitamin D deficiency testing and supplementation in adult medical practice

Abstract

Vitamin D testing and supplementation are common in adult medical practice, but their clinical use has become uneven. Severe vitamin D deficiency causes osteomalacia, secondary hyperparathyroidism, bone pain, proximal muscle weakness, and increased skeletal fragility. In selected high-risk adults, testing and treatment are clearly justified. In contrast, routine screening of asymptomatic adults and broad supplementation for non-skeletal disease prevention are not well supported by trial evidence. This review evaluates vitamin D deficiency testing and supplementation in adult practice, with attention to bone health, falls, fatigue, immune claims, overtesting, toxicity, and high-risk groups. PubMed-indexed guidelines, systematic reviews, randomized trials, meta-analyses, and toxicity reviews were examined. Current evidence supports targeted testing in adults with clinical suspicion of deficiency, osteoporosis or fragility fracture, osteomalacia features, malabsorption, chronic kidney or liver disease, bariatric surgery, medicines affecting vitamin D metabolism, persistent hypocalcaemia, or other clear risk factors. The 2021 US Preventive Services Task Force found insufficient evidence to assess the balance of benefits and harms of screening asymptomatic community-dwelling nonpregnant adults. The 2024 Endocrine Society guideline also advised against routine 25-hydroxyvitamin D testing in generally healthy populations without established indications. Supplementation remains important for deficient patients and for maintaining recommended intake in those with low dietary or sunlight exposure. However, large trials in generally healthy adults do not support vitamin D supplementation as a stand-alone strategy for preventing fractures, falls, cardiovascular disease, cancer, or most immune outcomes. High intermittent doses may increase fall risk in some older adults. Toxicity is uncommon but clinically important and usually results from excessive supplementation, prescription error, or unmonitored high-dose use. Adult practice should therefore shift from reflex testing and non-specific supplementation toward risk-based assessment, safer dosing, and outcome-focused follow-up.