In general, magnesium and vitamin D can be taken together, and magnesium plays a role in vitamin D metabolism. That said, it does not mean everyone needs to supplement both. If symptoms persist during vitamin D use—such as cramps, sleep issues, or irritability—a clinician may consider whether magnesium intake is adequate. Safety matters: in kidney disease, the balance of vitamin D, magnesium, and calcium can be more delicate, so avoid uncontrolled dosing. Practically, taking them at the same time is usually fine; people with sensitive stomachs may prefer magnesium with meals. If you take certain medications (e.g., thyroid drugs or some antibiotics), timing separation from magnesium may be needed.