Provided that supplements are taken in the amounts recommended on the pack by the manufacturer or retailer, and the Safe Upper Levels (SUL) are not exceeded by combining too many different supplements, then it is highly unlikely that supplements will cause any harm.
Safe Upper Levels (SUL) were established for most vitamins and minerals in a 2003 report by the Expert Group on Vitamins and Minerals. The report determined the maximum daily intake of nutrients from both supplements and diet that it is safe to consume on a long-term basis. These are based on consumption of a typical European diet and are generally far higher than the Nutrient Reference Value or amount that would be in a typical multivitamin.
View the Recommended Intake Guidelines for vitamins and minerals.
Water soluble vitamins – such as the B group vitamins and vitamin C – cannot be stored by the body to any great extent, so if someone takes more than their body needs, it will simply be excreted in their urine.
The fat soluble vitamins, vitamin A and vitamin D can accumulate in the body, but pose no danger to health if consumed within the SUL indicated for them. The exception is in pregnancy, when large amounts of vitamin A may pose a risk to the developing infant. Pregnant women should seek advice from a doctor before taking a supplement containing vitamin A and people with blood clotting disorders should seek a doctor’s advice before taking supplements containing vitamin E or vitamin K as these have an effect on blood clotting mechanisms.
Some minerals may also cause unwanted side effects if taken at doses above the SULs. In 2006 the food supplements industry agreed, with the Food Standards Agency and the Department of Health to the use of warning statements for certain nutrients present in food supplements above agreed specified levels. For example, very high intake of zinc (25 mg and above) can interfere with iron absorption and if taken over a long period of time can lead to anaemia. Responsible manufacturers will ensure that a warning statement to this effect will be on the label of any food supplement containing 25mg or above of zinc.
It is important to note that quantities in excess of what we need or what is recommended may be harmful for a few individuals and that individual sensitivities and variations in response can occur, so people are advised to seek medical advice if any unexpected symptoms appear whilst taking a particular supplement.