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Large supplemental doses may increase the amount of oxalate in the urine. In susceptible people, this can contribute to the formation of **calcium oxalate kidney stones**.
People who already have:
* kidney disease
* a history of kidney stones
* disorders that increase oxalate absorption
should be particularly cautious with high-dose vitamin C supplements.
Getting vitamin C from ordinary foods such as citrus fruits, berries, peppers, and vegetables is generally not the concern. The issue is primarily concentrated supplements taken in much larger amounts than the body requires.
## 4. Niacin — Vitamin B3
Niacin is an essential B vitamin, but high doses of nicotinic acid have also been used medically to influence cholesterol levels.
At nutritional doses, niacin is not normally associated with liver damage.
At pharmacological doses, however, it can cause elevations in liver enzymes and, in some cases, clinically significant liver injury.
Certain sustained- or extended-release formulations have been particularly associated with liver toxicity when used improperly.
Possible warning signs can include:
