Dear Bones: Lucy and MIT Nutritionist Anna Jasonides commend you for thinking about your calcium intake and striving to get enough. Calcium is one of Jasonides’s favorite topics, and with good reason. “It’s the most abundant mineral in the body,” she exclaims. “And you don’t just need it for your bones. Calcium does so much else.”
The “so much else” is a long list, Jasonides tells Lucy. But among other things, calcium is involved in blood clotting, muscle contraction, and the function of nerves. It also helps to release hormones and enzymes that affect almost every part of the body. “We lose calcium through our skin, nails, hair, sweat, and other excretions every day, but our bodies don’t produce new calcium,” she explains. “That’s why we need to continually replenish our body’s supply.”
An individual’s daily calcium requirement varies by sex and with age, but a woman aged 19–50 should be getting 1,000 mg. a day—preferably from “real food,” Jasonides says. “Dairy foods provide the most concentrated source, with most having about 300 mg. of calcium per standard serving.” If you don’t “do dairy,” you’ll probably need more servings of non-dairy foods to get the calcium you need. “Plants like kale, collards, broccoli, white beans, almonds, and tofu set with calcium are among the best plant sources,” she notes. “Spinach and beet greens are not a good source, because their calcium is bound to oxalate acid and is, therefore, not so available for digestion.
“And, though not a plant, I have to mention canned salmon and sardines, two of my favorite go-to sources for a quick, nourishing meal—and a great source of dietary calcium,” she adds. “It’s the bones that offer up the calcium there.”
If you can’t meet your calcium needs through diet, Jasonides says, calcium supplements are acceptable. “You are right that TUMS—or calcium carbonate—is hard to absorb,” she notes, “but it is still an acceptable source. The calcium in TUMS will be better absorbed if there is acid in the stomach, so try to take it with food. Calcium citrate is a more absorbable form—this is what’s used in fortified orange juice and other fortified foods—but in pill form, you will have to take more, because the dose in each pill is lower.”
In any case, Jasonides recommends focusing only on the total number of milligrams you’re getting each day without worrying about the absorption rate. “On average, only 30 percent of the calcium ingested from any source is absorbed by the small intestine,” she notes. But, she cautions, this is also a case where more is not better. “For someone who needs 1,000 mg. of calcium a day, the toxicity level is 2000 mg.,” she notes, “so if you’re taking a supplement, don’t take more than you need.”
Lucy thanks you for a question about a topic that is not only near and dear to the heart of our favorite nutritionist, but also a topic so important to our health. Lucy plans to pull out her favorite calculator and take a careful look at her daily calcium intake, and she urges you, and all her other readers, to do the same. —Lucy