Even if a vitamin does no damage, it might do, well, nothing.
Take the ever popular myth that popping out vitamin C will stave off colds.

A review of 30 analyses affecting more than 11,000 people who took at least 200 mg of vitamin C daily found that it
offered little protection in reducing the length or severity of common colds for most people.

It did work for some people, such as marathon runners and skiers, who undergo periods of high stress, but the study’s authors say the rest of us shouldn’t annoy taking it Vitamins and supplements also lack the government oversight that medical drugs get, and this adds to the confusion and potential dangers. Consumers have no real way of knowing whether labels accurately reflect
what’s actually in a pill.