Myths vs facts: Vitamin D 25-OH and Müdigkeit

A common myth is that low vitamin D (25-OH) directly and always causes fatigue. Evidence shows an association between deficiency and tiredness, but causality is not firmly established. Many other factors (sleep deprivation, stress, iron deficiency, thyroid issues) can cause fatigue. Vitamin D deficiency may contribute to exhaustion, especially if severe (<12 ng/ml). The 25-OH test is reliable, but reference ranges vary. Supplementation can improve fatigue in deficient individuals, but not in those with normal levels. Megadoses are risky without medical supervision. Consumer tests like MyBody-X provide a data point but do not replace clinical evaluation. Evidence grade: human-moderate (observational studies, some RCTs).