A dietary supplement is intended to provide nutrients that may otherwise not be consumed in sufficient quantities.

Supplements as generally understood include vitamins, minerals, fiber, fatty acids, or amino acids, among other substances. U.S. authorities define dietary supplements as foods, while elsewhere they may be classified as drugs or other products.

There are more than 50,000 dietary supplements available. More than half of the U.S. adult population (53% - 55%) consume dietary supplements with most common ones being multivitamins.

These products are not intended to prevent or treat any disease and in some circumstances are dangerous, according to the U.S. National Institutes of Health. For those who fail to consume a balanced diet, the agency says that certain supplements "may have value."

Most supplements should be avoided, and usually people should not eat micronutrients except people with clearly shown deficiency. Those people should first consult a doctor. An exception is vitamin D, which is recommended in Nordic countries due to weak sunlight.