Short answer: yes.  Fat-soluble supplements, however, are more of a problem than water-soluable. A meta-analysis of existing studies (Journal of the American Medical Association, February 2007)   determined that overdoses of beta carotene, vitamin A, and vitamin E—all fat-soluable—may increase mortality. The risks of vitamin C, which is water-soluble, were not clear-cut and needed more study.  Complementary Prescriptions, however, takes issue with the JAMA study, saying it was flawed in focusing on research that showed dangers while not looking at research that demonstrated positive effects. 

Some clarification on vitamin types:

Fat-Soluble: These include vitamins A, D, E and K, which are stored in body fat tissues.  Too many of these can build up in the liver, brain and heart and may be toxic. Dangerous levels, though, are typically many times the suggested normal dose.

Water-Soluble: B-complex and vitamin C are water-soluble, which means excess amounts are eliminated from the body in the urine, making them less dangerous.

Natural Sources:  Your best bet for vitamins is to get them from vegetables, fruits, fish oils, low-fat dairy products, nuts, seeds, and whole grains. You’re far less likely to overdose on carrots than on beta-carotene.

The Annie Appleseed Project has a comprehensive overview of vitamins and their sources.

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