Vitamin-D Selbsttest: what are common causes?

A Vitamin D self-test measures 25-hydroxyvitamin D levels, typically from capillary blood. Common causes of low levels include: insufficient sun exposure (especially in winter, northern latitudes, or with darker skin), low dietary intake (fatty fish, eggs, mushrooms), malabsorption (celiac disease, Crohn's, after gastric bypass), obesity (vitamin D is sequestered in adipose tissue), kidney or liver disease (impaired hydroxylation), and certain medications (antiepileptics, glucocorticoids). Age and pregnancy also increase requirements. A self-test provides a preliminary indication but does not replace medical diagnosis. The measurement is often reliable, but preanalytical errors (e.g., improper blood collection) can affect results. If values are abnormal, a physician should investigate underlying causes and consider supplementation. Evidence for causes is strong (human-strong); test accuracy varies by kit.