What to watch with Vitamin D 25-OH and Schlaf?

Low vitamin D (25-OH) levels have been linked to sleep disturbances such as shorter sleep duration, poorer sleep quality, and increased daytime sleepiness. However, the evidence is mostly observational; randomized controlled trials show mixed results. A blood test for 25-hydroxyvitamin D is necessary to confirm deficiency before supplementing. Over-supplementation can cause hypercalcemia and kidney stones. Genetic tests for vitamin D receptor (VDR) variants have limited predictive value for actual serum levels. For sleep issues, also consider sleep hygiene, stress, and melatonin. Consult a physician for persistent sleep problems.