Niacin from food is not the same risk as high-dose pills. The danger usually comes from large supplemental doses, especially extended-release or sustained-release forms used without medical supervision.
4. Vitamin C in Very High Doses
Vitamin C is water-soluble and important for immune function and collagen production, but very large doses are not harmless for everyone. The NIH notes that high vitamin C intake may increase urinary oxalate and uric acid excretion, and this can contribute to kidney stone risk in some people.
A large cohort study found supplemental vitamin C intake was associated with a higher risk of kidney stones in men. People with a history of kidney stones, chronic kidney disease, or oxalate problems should be extra cautious with high-dose vitamin C powders or tablets.
5. Iron Supplements
