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Guide to Vitamins

Should I Take a Calcium Supplement?

Kids need calcium for growth. Adults need it for bone health. Who should take it in pill form?

Illustrations by Kieran Blakey

This story is a part of The Elemental Guide to Vitamins. Here are the vitamins and supplements that are covered: multivitamins, vitamin D, vitamin C, calcium, B vitamins, omega-3, vitamin E, fiber, protein, and probiotics.

CCalcium is an essential mineral that the human body uses to make healthy bone and teeth. It’s found in a lot of foods — everything from leafy greens and legumes to fish like sardines and salmon. But on a per-serving basis, dairy foods are the real calcium champs.

(Other food groups — especially leafy greens like kale — also contain calcium, but a person would need to consume a lot to get the same amount as, say, a glass of milk. One cup of milk contains five times the calcium as a cup of kale, and a cup of cheese contains about 20 times the calcium as kale.)

Kids need calcium for growth and development. Adults need it to maintain bone health. Especially later in life, bone tends to break down more rapidly than the body can build it up. Over time, this breakdown can lead to osteoporosis — a condition in which bones become so porous and fragile that fractures are a concern.

These concerns may be heightened in older women; estrogen ramps up the activity of bone-building osteoblasts. And because a woman’s estrogen levels usually decline following menopause, bone weakness is a predictable threat.

Since the body needs calcium to build bone, it makes sense that taking a calcium supplement could help promote healthy growth in kids and also prevent bone breakdown and weakness in adults. Especially in older adults who don’t eat much dairy, it was once thought that calcium supplements were an effective safeguard against osteoporosis. But the evidence in support of all these presumptions is spotty.

“A lot of foods nowadays are fortified with calcium, and so most people are getting a lot more from their diets than they realize.”

For one thing, the human gut struggles to absorb calcium when people consume the mineral by itself. A little vitamin D is needed to help facilitate the gut’s uptake of calcium. But the research on taking calcium with vitamin D to prevent age-related bone weakness is underwhelming. The U.S. Preventive Services Task Force says that, to date, there’s not good evidence that adults who take calcium and vitamin D enjoy a lower risk for bone fractures.

On the other hand, it’s possible that vegans, vegetarians, and other people who avoid eating dairy products may be low in calcium. Also, boys ages nine to 13 and girls ages nine to 18 are at risk for calcium shortfalls, per the National Institutes of Health. But even in these groups, it’s not clear that taking a calcium pill or calcium combined with vitamin D leads to health benefits.

“A lot of foods nowadays are fortified with calcium, and so most people are getting a lot more from their diets than they realize,” says Dr. Mark Moyad, the director of preventive and alternative medicine at the University of Michigan. He says people who don’t eat dairy still get lots of calcium from breakfast cereals, fortified orange juice, non-dairy “milks” like soy milk, and the other foods mentioned above.

What could go wrong from overdosing on calcium? Too much can cause constipation. And there’s some evidence — though again, it’s mixed — that calcium supplements may mess with the body’s absorption of iron and zinc, or increase a person’s risk for kidney stones.

Also, while calcium’s main job is to build bone and teeth, it also plays a role in the healthy function of nerves, blood vessels, and muscle — including the heart. But, surprisingly, there’s evidence that taking a calcium supplement may promote heart trouble. A large 2011 BMJ study found that women who took calcium supplements — either with or without vitamin D — were at greater risk for heart problems, and heart attacks in particular.

“After taking a calcium supplement, the blood level of calcium increases substantially,” says Dr. Ian Reid, a distinguished professor of medicine at the University of Auckland in New Zealand and co-author of the BMJ study. “These changes have been associated with increases in blood pressure and increases in the tendency of blood to clot,” he adds. “Either of these could contribute to increased cardiovascular risk.”

The connection between calcium supplements and heart problems is not rock solid, and Reid says lower-dose supplements (those containing just 100 or 200 milligrams) may not come with the same risks. But he says older people and those with heart trouble should be wary. “Since there is no clear evidence that taking calcium supplements confers any benefits, there is little justification for giving these supplements to any older person,” he says.

The bottom line: For most people, taking calcium supplements likely isn’t needed. But for younger folks, if someone is 100% certain that he or she is not getting enough calcium from diet alone, a supplement may help fill in those shortfalls.

This story is a part of The Elemental Guide to Vitamins.

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Markham Heid

Markham Heid

I write about health, science, and psychology. My work has appeared in Time magazine, the New York Times, Vice, and elsewhere. I live in Germany.