Overview
- Vitamin D status is assessed by the 25‑hydroxyvitamin D blood test, with results reported in ng/ml or nmol/l and a conversion factor of 2.496.
- The RKI cites 30–50 ng/ml as an optimal range, while some laboratories such as Labor Enders apply different cutoff values for deficiency and oversupply.
- EFSA sets a tolerable upper intake for healthy adults at 100 µg daily (4000 IU), and the BfR warns against long‑term use of high‑dose preparations.
- Supplement‑driven overdoses can raise blood calcium and cause nausea, vomiting, abdominal pain, kidney damage, heart rhythm problems and, in severe cases, life‑threatening outcomes.
- Clinicians recommend testing before any high‑dose regimen, dosing should be individualized, a common rule of thumb is that 10,000 IU raises serum levels by about 1 ng/ml, and risk groups include people with limited sun exposure, darker skin or certain chronic conditions or medications.