Is Vitamin D 25-OH useful for fatigue?

Whether Vitamin D (25-OH) is useful for fatigue depends on baseline status. In individuals with deficiency, supplementation can improve fatigue and general well-being. However, in those with sufficient levels, randomized controlled trials show no consistent benefit. Home test kits for Vitamin D are convenient but serve as screening tools, not diagnostic replacements; accuracy depends on sampling technique. The evidence is moderate: human observational and some interventional studies support benefit in deficiency, but effect sizes are small and not universal. Safety note: high-dose Vitamin D can cause toxicity (hypercalcemia), so supplementation should only follow confirmed deficiency. For chronic fatigue, other causes (thyroid, iron, sleep) should be investigated. MyBody-X tests can provide insights but are not a substitute for professional medical advice.