Calcium carbonate contains more elemental calcium (40% vs 21%) and is cheaper, but requires stomach acid for absorption — take it with meals. Calcium citrate absorbs well on an empty stomach and is better suited for seniors and those with low stomach acid. Citrate also causes fewer gas and constipation issues.

Yes, over 2,500 mg of calcium per day (from food and supplements combined) can increase kidney stone risk and calcium deposits in blood vessels. Some studies also point to increased heart disease risk with excessive calcium supplementation. Ideally, 50-70% of calcium comes from food, with the remainder from supplements.

Vitamin D is essential for calcium absorption from the intestine — without adequate vitamin D, the body absorbs only 10-15% of calcium from food (up to 40% with vitamin D). Taking calcium without vitamin D is therefore far less effective. Most quality calcium supplements also contain vitamins D3 and K2.

Vegetarians and vegans can get calcium from dark green vegetables, tofu, almonds, and calcium-fortified plant milk. However, plant-based calcium is often harder to absorb due to oxalates and phytates. Calcium-fortified foods and supplements ensure adequate intake when dietary options are limited.

Take calcium carbonate with meals for better absorption. Calcium citrate can be taken any time. Do not take more than 500 mg at once — split larger doses across multiple servings. Do not take calcium together with iron, as they compete for absorption. An evening dose may also support better sleep.