Understanding Calcium: Supplements, Calcium Carbonate, Calcium Citrate, and More

Are you getting enough calcium in your diet? Maybe not -- especially if you're a woman or a teenage girl. Although Americans have improved their calcium intake in recent years, we're still not getting enough to maintain our bone health.

How much is that? It depends on your age. According to the Institute of Medicine, the recommended daily intake of calcium is:

• 1-3 years: 700 milligrams daily
• 4-8 years: 1,000 milligrams daily
• 9-18 years: 1,300 milligrams daily
• 19-50 years: 1,000 milligrams daily
• 51-70 years: 1,200 milligrams daily for women; 1,000 milligrams daily for men
• 71 and older: 1,200 milligrams daily

The Institute of Medicine notes that most in the US get enough calcium except for girls 9 to 18 years old. Although women’s recommended calcium needs increase with menopause, postmenopausal woman taking supplements may also be at increased risk of getting too much calcium.

"We know that peak bone mass occurs around age 30, so it's very important in childhood and adolescence to have a healthy intake of calcium early on," says Marcy B. Bolster, MD, professor of medicine in the division of rheumatology and immunology at the Medical University of South Carolina and director of the MUSC Center for Osteoporosis and Bone Health.

"After age 30, we start to gradually lose bone, and that loss accelerates for women at the time of menopause. So it's very important to stave off bone loss with adequate calcium intake."

Your health care provider may recommend calcium supplements. However, with so many choices of calcium supplements,where should you start? Here's what you need to know.

What kind of calcium supplement should you take?

"I tell my patients to take the kind that they tolerate best and is least expensive," Bolster says. She says she recommends calcium carbonate because "it's inexpensive, won't cause discomfort, and is a good source of calcium."

Some people may have problems producing sufficient stomach acid, or may be taking medications that suppress acid production. For them, says Puzas, a calcium citrate supplement might be better because it "dissolves a little better than calcium carbonate for these people."

What about other types of supplements, like calcium plus magnesium, coral calcium, and so on? Not necessary, the experts tell WebMD, although they note that supplements that combine calcium with vitamin D -- which is essential for the body to appropriately absorb calcium -- provide an added benefit.

What calcium supplement dose is best?

The body can absorb only about 500 milligrams of a calcium supplement at any one time, says Puzas, so you can't just down a 1000-mg supplement first thing in the morning and call it a day.

Instead, split your dose into two or three servings a day. "The best way to take it is with a meal; calcium is absorbed better that way," Puzas says. If your daily diet includes calcium-containing  foods and drinks, you may not need multiple doses.

Can you take too much calcium?

According to the National Institutes of Health, the upper limits of daily intake of calcium for people between the ages of 19 and 50 is 2,500 milligrams and for those 51 and older, it’s 2,000 mg.

Calcium supplements rarely cause excessive calcium levels in the bloodstream. "It doesn't hurt you, but it's not particularly beneficial, either," Puzas says.

One exception: people who have a tendency to make kidney stones. "You might make larger and more frequent stones with unusually high doses of calcium."

"There's really no point in taking more calcium than about 1,200-1,500 milligrams a day," Bolster stresses.

Can I skip calcium supplements and get what I need from my diet?

Yes. But it's going to take some work.

How can you tell if you're getting enough calcium? Try tracking your calcium intake for a week.

"Write down what you eat for a week, figure out how much calcium is in what you've eaten during that time," says J. Edward Puzas, MD, a professor of orthopedics and director of orthopedic research at the University of Rochester Medical Center in New York. "Then divide by seven. I'll bet you'll be well under 1,000 milligrams."

When he first tried this test, Puzas himself found that his calcium intake was only about 700 milligrams per day -- "and I knew better and was trying to do good things!"

Some of your best sources of dietary calcium are yogurt (over 400 milligrams per 8-ounce serving), nonfat milk (about 300 milligrams per serving), and cheeses like mozzarella and cheddar (between 275 and 315 milligrams per serving). Some dark green vegetables, like spinach, are fairly high in calcium as well.

Keep in mind that there's really not that much difference between getting calcium in a supplement and calcium in food.

"Ideally, if you have a good, healthy diet, and get all your nutrients including calcium from that, that's best," says Puzas. "But the calcium in food and the calcium in supplements is identical."

What would a good, calcium-rich diet look like?

If you drank a glass of milk (300 milligrams of calcium) with a calcium-fortified cereal for breakfast (400 milligrams of calcium), you'd get 70% of the 1,000-milligram recommended daily intake of calcium for an adult age 19-50 with that meal alone.

Or, you could have a carton of yogurt (415 milligrams of calcium) with 6 ounces calcium-fortified orange juice (250 milligrams of calcium) for a total of  665 milligrams of calcium. Calcium-fortified foods -- such as cereals, some juices, and soy milk -- are excellent sources of the mineral, experts tell WebMD.

Later that day, if you add 3 ounces of canned salmon(180 milligrams of calcium) on your lunch salad, snack on 1.5 ounces of cheddar cheese (306 milligrams of calcium), have  half a cup of spinach with dinner (120 milligrams of calcium), and enjoy half a cup of ice cream for desert (85 milligrams of calcium), you would have gotten more than enough calcium for an average adult.

If you don't eat dairy products, good sources of calcium include tofu made with calcium sulfate (138 milligrams of calcium per half-cup serving); leafy dark green vegetables such as spinach, kale, or turnip greens; and calcium-fortified foods.

So do your best to get your calcium the tasty way. But if you can't, a simple, inexpensive calcium supplement can help keep your bones just as healthy.