Supplement shelves can give the impression that almost everyone needs something. Yet for generally healthy adults, a review of 84 studies found that routine vitamin and mineral supplements offered little or no protection against cardiovascular disease, cancer or early death.
Taking a supplement without a clear reason may also cause harm. High doses of some water-soluble vitamins can cause harm, and too much vitamin B6, for example, has been linked to nerve damage. Some fat-soluble vitamins, particularly vitamin A, can accumulate and cause toxicity when taken in excess.
A diagnosed deficiency is one reason to take a supplement. Other evidence-based reasons include folic acid before and during early pregnancy, vitamin B12 for people who cannot obtain enough from food and the 10 micrograms of vitamin D that UK guidance recommends people consider during fall and winter.
Once there is a sound reason to take a supplement, timing can sometimes affect absorption. Usually, "timing" concerns meals, drinks and other medicines rather than a perfect hour on the clock.
Iron: The fussiest supplement
