Wiktionary
n. (context medicine English) any substance, such as a vitamin or mineral taken as a supplement to food to replace nutrients that would otherwise be missing in a person's diet
Wikipedia
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.
Usage examples of "dietary supplement".
Vitamin C wasn't the only dietary supplement humans required on this misbegotten planet, but it was probably the one whose absence would have the quickest consequences.
One night he watched a report on the fertilization of the Antarctic Ocean with iron dust, which was to act as a dietary supplement to phytoplankton, a population that was shrinking at an alarming rate for no obvious reason.
She picked a container of fortified dietary supplement and sipped at it unhappily.
This time the boy responded with a suggestion for an unpalatable dietary supplement.