Vitamin D-Check

Serum 25-hydroxyvitamin D measurement. At €18.65 (plus blood draw), an affordable seasonal screen for anyone living at Leipzig's latitude (51°N) where UV-driven synthesis is limited October through March.

25-hydroxyvitamin D is the standard biomarker for assessing vitamin D status. It reflects combined input from cutaneous UV-B synthesis, dietary intake, and supplementation. At Leipzig's latitude (51°N), effective skin synthesis of vitamin D occurs only from approximately April through September, and even then is limited by clothing, sunscreen use, and indoor lifestyles. Estimates suggest 60–80% of Central European adults have suboptimal vitamin D levels during winter months. The clinical impact extends beyond the well-known role in calcium absorption and bone mineralisation. Vitamin D receptors are expressed in immune cells, muscle tissue, cardiovascular endothelium, and brain neurons — supporting its associations with immune regulation, muscle strength, cardiovascular health, and mood. Deficiency is defined as below 20 ng/mL (50 nmol/L), insufficiency as 20–30 ng/mL, and optimal as 30–50 ng/mL. Levels above 100 ng/mL carry toxicity risk from supplementation (not achievable through sunlight alone). The test is particularly relevant for: individuals with limited sun exposure, dark-skinned individuals at northern latitudes, older adults (cutaneous synthesis declines with age), obese individuals (vitamin D is sequestered in adipose tissue), and anyone experiencing unexplained fatigue, muscle weakness, or bone pain. Supplementation does not need to be stopped before testing — the test measures current status including supplementation, which is the clinically relevant question.