Too many supplements — especially single-nutrient ones — provide too much of a nutrient, often more than our body can process. Not only is that a waste of money, but it can also be dangerous. While many people worry about a nutrient deficiency, exceeding the upper limit can put undue stress on your kidneys, and can sometimes be fatal.
Fat-soluble vitamins A, D, E and K and minerals such as magnesium, iron and potassium pose the biggest risk, while excessive calcium (hypercalcemia) can lead to kidney stones and cardiac arrhythmia.
Here, we’re guided by RDA, because we believe a supplement should be supplemental to your diet.