For most people, it is safe to eat foods containing calcium and to take calcium supplements that together do not exceed the tolerable upper intake level of 2.5 grams of calcium per day. This upper level for daily calcium intake in adults is the highest level that likely will not pose risks of unwanted side effects in the general population. The upper level of 2.5 grams a day is an average recommendation for all healthy people who are older than a year, regardless of gender.
Consuming too much calcium—in excess of 5 grams a day, or 3 grams a day in people with existing kidney problems (4)—can lead to several harmful side effects. Most of these side effects result from people taking too many calcium supplements. Rare harmful side effects from excess calcium include kidney stones (5), hypercalcemia (too much calcium in the blood), and kidney failure (1). In addition, excessive consumption of milk (which is high in calcium) and some types of antacids, especially antacids containing calcium carbonate or sodium bicarbonate (baking soda), over a long period of time can cause milk-alkali syndrome, a condition that can also lead to calcium deposits in the kidneys and other tissues and to kidney failure (4, 6, 7).