Myths vs facts: Vitamin D 25-OH and Schlaf

The claim that low vitamin D (25-OH) directly causes poor sleep is a common myth. While vitamin D receptors exist in brain areas regulating sleep, and observational studies link low levels to worse sleep quality, randomized controlled trials show inconsistent benefits from supplementation. Confounders like sunlight exposure, physical activity, and overall health are often overlooked. Consumer DNA tests (e.g., CLOCK gene variants) have very weak predictive value for sleep. Measuring 25-OH vitamin D is useful for assessing deficiency, but using it alone to explain or treat sleep issues is not evidence-based. For genuine sleep disorders, a comprehensive medical evaluation is necessary.