The advice is simple: to keep bones strong and ward off osteoporosis, especially as you age, get enough calcium – 1,000 milligrams (mg) per day if you’re younger than 50; 1,200 mg if you’re older. You can get calcium in your diet by eating green leafy vegetables; consuming low-fat milk, yogurt and cheese; or opting for calcium-fortified juice, bread and cereal. If you don’t get enough calcium in your diet, you'll need to take a calcium supplement daily. But you may need to know more about calcium to ensure your body gets what it needs.

Calcium Supplement Basics

1. Make sure you check the amount of elemental calcium in a supplement; that’s what your body will actually absorb.

2. Take several smaller doses per day, because your body can absorb only 500 mg at a time.

3. Your body needs vitamin D to use calcium most efficiently, so look for calcium supplements that contain both.

Calcium “Cheat Sheet”
There are several different types of calcium. Check out the chart below for the three most popular types, and to help determine the best calcium supplement for you. Other kinds, such as calcium gluconate and calcium lactate, have very low amounts of elemental calcium and are not recommended. Coral calcium and oyster-shell calcium products also are best avoided because they may contain lead.

Calcium Type  Pros      Cons
Calcium citrate
(Citrical, Solgar) 21% calcium
Most easily absorbed Most expensive; doesn’t contain much elemental calcium
Calcium carbonate
(Tums, Caltrate, Rolaids) 40% calcium  
Least expensive; has more elemental calcium Must be taken with meals or glass of acidic (orange) juice; may cause gas or constipation
Calcium phosphate (Posture) 39% calcium   Does not cause gas or constipation; easily absorbed More expensive than calcium carbonate

Precautions: Don’t take more than 1,200 mg of calcium (in supplement form) a day unless instructed by a doctor or dietitian. Excess amounts (more than 2,500 mg a day) can harm the kidneys and can reduce the absorption of other minerals like iron, zinc and magnesium. Also, avoid taking calcium supplements at the same time as some kinds of medications, including bisphosponates like alendronate (Fosamax) and ibandronate (Boniva) and certain antibiotics, because it can block their absorption by the body.