Excess vitamin E can cause headaches, diarrhea and increased blood pressure. In time, large doses of niacin can lead to liver toxicity. Too much vitamin C can cause diarrhea or liver problems. Too much vitamin B6 can lead to muscle weakness and numbness of the feet and hands. A deficiency of one nutrient can be caused by an excess of another.
Excessive zinc decreases copper and iron absorption.
Excessive vitamin C decreases copper absorption. And recently, researchers at the Grand Forks Human Nutrition Research Center, North Dakota, found that chromium picolinate supplementation leads to iron deficiency. Men taking 200 micrograms of chromium picolinate were iron deficient in as little as two months. The chromium picolinate binds with transferrin, the substance responsible for transporting iron in the blood. Supplements provide the illusion of caring for your health, but unless you're eating three squares a day, you're not getting the benefits of food itself.