Can you overdose on vitamins

Yes — more isn't better.

• Fat-soluble A, D, E, K build up; long-term high doses are toxic (vitamin A is risky in pregnancy).
• Excess iron harms the liver and is dangerous for children.
• Too much zinc causes copper deficiency; B6 above 100 mg a day long term can damage nerves.
• Excess water-soluble C and B mostly leaves the body, but huge doses still upset the stomach.

Stick to the label dose and don't double up the same nutrient from several products (add up your multi, separate D and ZMA).