How Much Calcium Do You Really Need?

A major medical panel suggests that many women don’t need calcium and vitamin D pills to protect against bone fractures. Not all experts agree

by Leslie Pepper
Photograph: Christopher Silas Neal

The promise is appealing: If you’re religious about taking calcium supplements, you can fend off the bone thinning known as osteoporosis and prevent the debilitating fractures that often come with the condition. That’s why in 2012, Americans spent $1.2 billion on calcium supplements and $652 million on vitamin D pills, which can boost thebody’s absorption of calcium.

But recently the effectiveness of those supplements has been questioned. Last year, after reviewing 16 randomized, controlled studies as well as 28 observational studies, the U.S. Preventive Services Task Force concluded that daily supplementation with calcium and vitamin D does not protect healthy postmenopausal women from experiencing fractures and therefore cannot be recommended. The group also said that while data are sparse, there’s no evidence that supplementation will benefit premenopausal women either.

Does this mean we should toss our calcium and vitamin D supplements in the garbage? To answer that question, you first need to understand the reasons these supplements were recommended in the first place.

Why Your Body Needs Calcium and D
Bones seem solid, but their structures are continuously being broken down and renewed. During the breakdown phase, bone cells called osteoclasts dissolve old bone, explains Ethel S. Siris, MD, director of the Toni Stabile Osteoporosis Center at the Columbia University Medical Center. In the renewal phase, cells called osteoblasts pull calcium and other minerals from the blood. These minerals join with collagen (a protein that provides structure) to re-form bone tissue. The activities of the osteoclasts and osteoblasts are balanced so that the right amount of bone is always being created and destroyed.

When we reach our thirties, however, that balance begins to shift. The -breaking-down process becomes dominant, and women lose slightly more bone tissue than they build. That loss really accelerates for a few years after menopause, when estrogen levels plummet. Estrogen regulates the activity of the osteoclasts, and “in its absence, the osteoclasts become too aggressive and they suck in too much bone,” says Siris. This is why -osteoporosis—which affects 7.4 million women over 50—becomes such a significant danger after menopause.

But the bones aren’t the body’s only customer for calcium; the mineral is also essential to the functioning of the heart, muscles and nerves. “The body tries to maintain a constant level of calcium in the blood, so if you’re deficient, your body is going to take it from your skeleton, which is the biggest storage house for this mineral,” says Andrea Sikon, MD, chair of the department of internal medicine and geriatrics at the Cleveland Clinic. For this reason, an insufficient intake of calcium can speed up the weakening of bones.

A shortfall in vitamin D, which your body can manufacture if you’re exposed to sunlight, may also lead to brittle bones. That’s because you need a derivative of vitamin D called calcitriol to facilitate the intestine’s absorption of calcium.

The conventional recommendations for a daily intake of 1,000 milligrams of calcium and 600 international units of D (from all sources—food and possibly supplements) are intended to avert shortages that would end up weakening bones and leading to osteoporosis.

Preventing osteoporosis is a way to head off the fractures that often have terrible consequences. For instance, for a year after a hip fracture, women over 65 are twice as likely to die as they would have been without the injury. Since fewer than one in four American women get the recommended doses of calcium from food and many don’t spend enough time in the sun to get sufficient D (one study estimates 42 percent of Americans are deficient), most medical experts have urged the use of supplements to make up the difference.

First published in the March 2014 issue

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