Although national guidelines recommend that adult women get 1,000 to 1,200 milligrams (mg) of calcium a day, some experts think that's too much calcium. In an interview in the August 2015 Harvard Women's Health Watch, Dr. Walter Willett, chair of the Department of Nutrition at the Harvard T.H. Chan School of Public Health, said that women can do just as well on half that much.
"Essentially, I think that adults do not need 1,200 milligrams of calcium a day. The World Health Organization's recommendation of 500 milligrams is probably about right. The United Kingdom sets the goal at 700 milligrams, which is fine, too. It allows for a little leeway," says Dr. Willett.
The body gets the calcium it needs for basic functions by releasing calcium stored in bones into the bloodstream. The ongoing process of building bones and breaking them down is called bone remodeling. Bone density drops when bone breakdown outpaces bone formation. Scientists have reasoned that maintaining an adequate level of calcium in the blood could keep the body from drawing it out of the bones, thereby keeping bones strong. 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. The current recommendation is based on those studies.
But that may not have been a sound decision. "The recommendation was based on calcium balance studies that lasted just a few weeks. In fact, calcium balance is determined over the course of years," says Dr. Willett. In addition, several clinical trials during the last 20 years have shown little benefit—and some risk—from high levels of dietary calcium:
- Calcium and vitamin D supplements don't prevent fractures.
- High calcium intake alone—either from food or supplements—doesn't prevent hip fracture.
- High doses of calcium from pills increases the risk of kidney stones.
- Calcium supplements may increase the risk of heart attack.
- Higher levels of dietary vitamin D may be necessary to prevent bone loss.
Dr. Willett recommends going lower on calcium and higher on vitamin D than the guidelines suggest: 500 to 700 mg a day of calcium, and 800 to 1,000 IU a day of vitamin D. At that rate, you can probably get all or most of your calcium from food, especially if you have a serving or two of dairy products daily.
Read the full-length article: "How much calcium do you really need?"
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