Vitamin D-Test

Single-marker vitamin D status check measuring 25-hydroxyvitamin D. At €42.40 all-in, a practical seasonal screen for anyone at Dresden's latitude (51°N) where UV-driven synthesis is limited from October through March.

25-hydroxyvitamin D (25-OH-D) is the standard biomarker for assessing vitamin D status in clinical practice. It reflects the combined input from cutaneous UV-B synthesis, dietary intake, and supplementation, with a half-life of approximately 2-3 weeks that makes it representative of recent overall vitamin D exposure. At Dresden's latitude of 51°N, effective skin synthesis of vitamin D from sunlight occurs only from approximately April through September, and even during these months it is limited by clothing, sunscreen use, time spent indoors, and the angle of the sun. During the winter months, UV-B radiation at this latitude is insufficient to drive any meaningful cutaneous vitamin D production regardless of sun exposure duration. Population studies consistently show that 60-80% of Central European adults have suboptimal vitamin D levels during winter, with rates of frank deficiency (below 20 ng/mL or 50 nmol/L) reaching 30-40% in some surveys. Groups at particular risk include office workers, older adults (cutaneous synthesis efficiency declines with age), individuals with darker skin pigmentation, those who cover most of their skin for cultural or religious reasons, and obese individuals (vitamin D is sequestered in adipose tissue). The clinical significance of vitamin D extends well beyond its classical role in calcium absorption and bone mineralisation. Vitamin D receptors are expressed in immune cells, muscle fibres, cardiovascular endothelium, pancreatic beta cells, and neurons. Research has identified associations between low vitamin D status and increased susceptibility to respiratory infections, autoimmune conditions, muscle weakness, cardiovascular events, insulin resistance, and mood disorders — though the causal strength of these associations varies. Interpretation of results follows established thresholds: below 20 ng/mL (50 nmol/L) is deficiency; 20-30 ng/mL (50-75 nmol/L) is insufficiency; 30-50 ng/mL (75-125 nmol/L) is the optimal range. Levels above 100 ng/mL (250 nmol/L) carry toxicity risk, though this is achievable only through supplementation, never through sunlight exposure alone. Supplementation does not need to be stopped before testing — the test measures current status including supplementation, which is the clinically relevant question for dosing decisions.