How are Vitamin D 25-OH and Schlaf related?

The relationship between vitamin D (25-OH) and sleep is an active research area, but the evidence is moderate and not conclusive. Vitamin D receptors are present in brain regions regulating sleep-wake cycles, and observational studies have linked low vitamin D levels with poorer sleep quality, shorter sleep duration, and increased daytime sleepiness. However, effect sizes are small, and randomized controlled trials often fail to show significant sleep improvement from supplementation in non-deficient individuals. Confounders like sun exposure, season, and lifestyle further complicate the picture. Vitamin D deficiency should be diagnosed and treated, but supplementing solely for sleep improvement is not well-supported. Caveat: high doses can be toxic. MyBody-X offers blood tests for vitamin D as a screening tool, but interpretation should be done by a physician. The evidence is based on human studies of moderate strength; no clear genetic markers link vitamin D and sleep.