09/25/2024
How much calcium do you absorb from supplements?
Absorption from supplements is highest with doses of 500 mg or less . For example, the body absorbs about 36% of a 300 mg calcium dose and 28% of a 1,000 mg dose.
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.
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.
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.
Side effects of too much calcium via supplementation
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.
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.
Wondering how much calcium do you need? 500 to 700 milligrams of calcium through diet and 800 to 1,000 of vitamin D as a supplement should be adequate to preserve bone density....
