Overview
- Vitamin D status should be measured as serum 25(OH)D, with the RKI citing an optimal range of 30–50 ng/ml and acknowledging method and seasonal variability.
- The BfR advises against precautionary self-supplementation, recommends up to 20 µg vitamin D per day from supplements, and warns not to exceed 100 µg total daily intake.
- Routine D+K2 pairing is not a universal rule, as the Verbraucherzentrale finds no reliable basis for blanket co‑use and patients on vitamin K–antagonists require medical advice.
- Vitamin D can support intestinal magnesium absorption but does not justify uncritical combined products; magnesium supplements are limited to 250 mg/day by the BfR due to diarrhea risk, with higher therapeutic doses used under supervision.
- B12 deficiency risk is elevated in vegans, older adults and those with absorption issues and is diagnosed by blood tests with treatment via supplements or injections, while B6 deficiency presents with dermatologic, hematologic and neurologic signs tied to malabsorption, drugs or alcohol.