Combining supplements will not normally interfere with the way they work and in some cases may be beneficial, for example vitamin C helps iron absorption. However, certain supplements may interact with each other. There is competition within the gut for the absorption of different minerals and a large dose of one might decrease the absorption of another. Therefore a multivitamin and/or mineral product is best for all-round supplementation because it has been designed to deliver nutrients in the right balance.

Before combining supplements, people should consult a health care practitioner or the product manufacturer.  It is also important to check that the daily amount taken of each particular nutrient does not exceed Safe Upper Levels.