What happens if we exceed the RDAs?

The Expert Group on Vitamins and Minerals, reporting for the Foods Standards Agency in 2003, concluded that vitamin and mineral supplements can be dangerous if taken in excess, and it published Safe Upper Levels (SULs) for mineral intake. For instance the SUL for zinc was put at 25 mg, above which there might be a danger to health — such as damage the immune system.

In the USA the equivalent is the Upper Level (UL), the 'maximum level of daily nutrient intake that is likely to pose no risk of adverse effects'. Here again, various dangers of exceeding such Upper Levels have been cited, such as:

  • an excess of selenium (which has been given a UL of 400 mcg) may lead to hair loss and brittle nails;
  • an excess of manganese (UL 11 mg) may result in muscle and nerve disorders;
  • an excess of calcium (UL 2500 mg) and iron (UL 45 mg) could cause gastrointestinal problems.

The general advice is that, if you really want to take vitamin and mineral supplements, without a medical need to do so, find a product that delivers no more than the Recommended Daily Allowance.

Useful website

http://dietary-supplements.info.nih.gov (US National Institute of Health, office of Dietary Supplements)

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