welche supplements brauche ich test — what are common causes?

The question 'which supplements do I need' is often driven by marketing or questionable tests. Common causes of actual deficiencies include: unbalanced diet (e.g., vegan without B12/iron/iodine), chronic gut disorders (Crohn's, celiac), certain medications (PPIs, metformin), or increased needs (pregnancy, athletes). A DNA test alone cannot reliably determine supplement needs – evidence for gene-based supplement recommendations is weak. More useful is blood testing for specific markers (vitamin D, ferritin, B12, folate) combined with a dietary assessment. Beware of tests that promise personalized supplements based on genetics: most effects are small and not clinically actionable.