There are two ingredients frequently found in supplements which can build up in the body and have toxic effects and so should NOT be included in a routine vitamin/mineral supplement. These are vitamins A and iron.
• Vitamin A: this is a fat-soluble vitamin and its levels can build up in the tissues causing skin problems, bone pain and fractures, nausea, vomiting and weakness. A good vitamin supplement will have beta carotene instead of vitamin A. If the body needs more vitamin A it can create it from the beta carotene, but if not then the beta carotene can be harmlessly excreted.
• Iron: this is frequently found in supplement tablets, and for most people it causes no problem. BUT one person in 300 has a condition called haemochromatosis which means that the iron will continue to build up in the body tissues. This especially occurs in the liver, pancreas and heart, leading to cirrhosis, diabetes and heart failure, and can be fatal. Unfortunately only a special blood test can confirm the presence or absence of haemochromatosis, so to include iron in a routine supplement could potentially kill or maim one person in 300.
Some people do need iron (for anemia), but it should be taken as a separate tablet, only after a blood test has confirmed that there is a need.