How much calcium do you really need?

How much calcium per day is recommended? Like many women, you may have memorized the minimum daily calcium requirement — 1,000 milligrams (mg) a day for women ages 50 and younger and 1,200 mg for women over 50 — and followed it faithfully in an effort to preserve your bones. But outside the United States, the recommended calcium intake is much lower. The World Health Organization recommends 500 mg of calcium a day and the United Kingdom sets the goal at 700 mg..

Why is 1,200 mg of calcium per day recommended?

 Adequate calcium is necessary for good health, and not just because it's a major component of our bones. It also plays a vital role in keeping our organs and skeletal muscles working properly. The body gets the calcium it needs for basic functions by releasing the calcium stored in our bones into the blood through bone remodeling—the process by which bone is constantly broken down and rebuilt.

Because bone density drops when bone breakdown outpaces bone formation, scientists reasoned that maintaining an adequate level of calcium in the blood could keep the body from drawing it out of the bones. In the late 1970s, a couple of brief studies indicated that consuming 1,200 mg of calcium a day could preserve a postmenopausal woman's calcium balance.

Based on those studies, in 1997 an Institute of Medicine panel raised the recommendation for calcium intake from 800 mg to 1,200 mg a day for women over 50. However, the recommendation was based on calcium balance studies that lasted just a few weeks. In fact, calcium balance should be determined over a much longer time period. Moreover, there isn't sufficient evidence that consuming that much calcium actually prevents fractures. Nonetheless, the recommendation has been carried forward since then.

The truth about how much calcium you need

In the past two decades, several clinical trials involving thousands of postmenopausal women have sought to determine how calcium intake affects the risk of hip fractures. In each study, women were randomly assigned to one of two groups — one to receive calcium and supplements of vitamin D (to aid calcium absorption) and the other to get placebo pills. After several years, the researchers looked at the number of hip fractures in each group. Here's what they found:

Calcium and vitamin D supplements don't prevent fractures. That finding came from two British studies reported in 2005. It was substantiated by a 2006 report from the Women's Health Initiative, which showed that 18,000 postmenopausal women who took a supplement containing 1,000 mg of calcium and 400 international units (IU) of vitamin D were no less likely to break their hips than an equal number who took a placebo pill, although the density of their hip bones increased slightly. Even that small change might have been due to the vitamin D rather than the calcium.

High calcium intake — from either food or pills — doesn't reduce hip fracture risk. This was the conclusion of a 2007 report by Swiss and American scientists who conducted an analysis of more than a dozen studies of calcium.

The downside of calcium supplements

The studies also revealed a couple of downsides to high levels of calcium supplementation, but not to calcium obtained through a regular diet:

An increased risk of kidney stones. In the Woman's Health Initiative, women taking the calcium–vitamin D combination had a higher risk of developing kidney stones than those who got the placebo. Although high levels of dietary calcium are thought to offer some protection against kidney stones, high doses of calcium from supplements may promote stone formation by increasing the amount of calcium that is eliminated in the urine.

An increased risk of heart attack. In a randomized study of 1,471 postmenopausal women conducted in New Zealand, 21 of 732 women who took 1,000 mg of calcium a day had heart attacks, compared with 10 of 736 who received a placebo. A 2010 analysis of 15 randomized controlled trials also linked calcium supplementation with an increased risk of heart attack.

Vitamin D is important, too

Vitamin D is also essential for healthy bones. In fact, the daily vitamin D requirement was first introduced to help prevent rickets — a condition in which developing bones are soft and can become bowed — in children.

Vitamin D is made in the skin through exposure to ultraviolet radiation in sunlight. However, the amount produced varies widely from person to person. People with darker skin produce less vitamin D than lighter-skinned people, and in all populations, the skin's ability to convert sunlight to vitamin D declines with age. Plus, if you follow the advice to reduce your risk of skin cancer by keeping covered and wearing sunscreen, you're also cutting your vitamin D production. Such variability has made it difficult for researchers to tell how much vitamin D people make in addition to the amount they consume in supplements. Evidence from studies that have measured blood levels of vitamin D indicates that levels in the high-normal range are optimal for building bone. To reach those levels may require taking 800 to 1,000 IU of vitamin D a day.

So how much calcium do you really need?

One thing the studies have taught us is that both calcium and vitamin D are essential in building bone. If you can get at least 700 mg of calcium from food, that should be enough. But if you're not sure, check with your doctor before just reaching for a calcium supplement.

However, getting enough vitamin D from sunlight and dietary source can be challenging. That's why so many doctors recommend a vitamin D supplement containing 800 IU to 1,000 IU daily.

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