welche supplements brauche ich test — which blood markers matter?

There is no single test that tells you which supplements you need. The most evidence-based blood markers for supplementation decisions are: vitamin D (25-OH-D), vitamin B12, ferritin (iron stores), magnesium (serum or RBC), and possibly the omega-3 index. These reflect actual deficiencies that supplementation can correct. In contrast, many commercial tests (e.g., NAD+ measurements) lack clinical validation: while oral NR/NMN raise blood NAD+ by 20–50%, no long-term human trial shows that this translates to better health or longevity. DNA-based supplement recommendations (e.g., from MyBody-X) rely on weak associations and are not a substitute for medical lab work. Important: supplementing without a proven deficiency can be harmful (e.g., excess vitamin B6 or selenium). Get the core markers checked by a doctor first. Evidence: human-moderate for vitamin D, B12, ferritin; mixed/unclear for NAD+ and DNA tests.