Do vitamin D supplements actually help?

They correct deficiency, which is genuinely common in people with limited sun exposure, darker skin, or covered clothing, and they support bone health. Supplementing beyond correcting deficiency hasn't reliably prevented cancer, heart disease, or infection in trials.

Deficiency is typically treated with a high weekly loading dose for 6-8 weeks, followed by a maintenance dose, with a repeat level after about three months.

Vitamin D needs magnesium and adequate calcium intake to work properly, and levels rise slowly — do not expect symptom change in a fortnight.