If I want to know the RDA for a nutrient, I check the National Institutes of Health, Office of Dietary Supplements site. Good site. Here’s Calcium. Depending upon one’s age and sex, the RDA is between 1,000 and 1,300 mg a day.
That’s a lot! You’d almost have to eat several servings of dairy a day to meet that. Hm. But I’m familiar with the work the Institute of Medicine puts behind their nutrient requirements so I typically don’t question it.
Lately I was questioning it, the calcium. I had read of communities in poorer countries that do just fine on a few hundred mg a day. Then I saw this older review:
Calcium Requirements In Man: A Critical Review, Postgraduate Medical Journal, 1978
Many official bodies give advice on desirable intakes of calcium but no clear evidence of a calcium deficiency disease in otherwise normal people has ever been given. In Western countries the usual calcium intake is of the order of 800-1000 mg/day; in many developing countries figures of 300-500 mg/day are found. There is no evidence that people with such a low intake have any problems with bones or teeth. It seems likely that normal people can adapt to have a normal calcium balance on calcium intakes as low as 150-200 mg/day and that this adaptation is sufficient even in pregnancy and lactation.
Not enough to change my mind. But this was enough:
How Much Calcium Do You Really Need?, Harvard Medical School, 11 September, 2019
Dr. Walter Willett, chair of the Department of Nutrition at Harvard T.H. Chan School of Public Health: “Essentially, I think that adults do not need 1,200 mg of calcium a day. The World Health Organization’s recommendation of 500 mg is probably about right.
How did we get to recommending double that more sensible 500 mg?
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. That wasn’t a sound decision, Dr. Willett says: “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.” Moreover, there wasn’t any evidence that consuming that much calcium actually prevented fractures. Nonetheless, the recommendation has been carried forward since then.
I’m tempted to see which entity sponsored those 1,200 mg/day studies. He goes on to describe studies that found:
- Calcium and vitamin D supplements don’t prevent fractures.
- High calcium intake—from either food or pills—doesn’t reduce hip fracture risk.
- Calcium supplements increase risk of heart attack.
- Calcium supplements increase risk of kidney stones.
Eating 500 mg/day of calcium is just fine, more than fine because it reduces risks for constipation, kidney stones, heart disease, and deficiencies of other nutrients that calcium competes with for absorption.