Dietary supplements are generally unnecessary and less effective than eating a balanced diet, according to Michael Krawinkel, a professor at Giessen University’s Institute for Nutritional Sciences in Germany.

Writing in a German nutrition magazine, Krawinkel noted that someone whose daily intake of vitamins and minerals did not always meet the recommended levels usually averaged sufficient amounts over the course of a week.

Claims of a deficiency of selenium, magnesium, or vitamins D, C or E in many people are often false, he said.

For some groups of people, however, dietary supplements are advisable, Krawinkel pointed out.

Expectant mothers should take folic acid in the first weeks of pregnancy, infants should be given vitamins K and D as well as fluorine, and people aged 65 and older would do well to take vitamin D regularly.