What you should know about calcium and supplements

By Delaney Sump, guest contributor

This article was originally published in September 2021

calcium supplements

Calcium is an essential nutrient to the human body, and there are vigorous debates in the research world about who might consider calcium supplementation and why. This conversation is particularly relevant when discussing how to support older adults and post-menopausal women who are at an increased risk of developing osteoporosis, considering one of calcium’s essential roles is helping to build and maintain strong bones. (Other nutrients such as phosphorus and vitamin D also play important roles in bone health.)

Bones and blood

Bones are made up of a protein called collagen, which provides the soft framework, and calcium, phosphate and other minerals that provide the solid structure of the skeleton so it can hold up the weight of our bodies and resist bending. About 99% of the calcium in our bodies is stored in bones; the remaining 1% is found in the blood and plays crucial roles in muscle contraction, nerve function, intracellular signaling and more.

Luckily, our bodies do a great job of maintaining our blood calcium. If the level of calcium in circulation drops for some reason (as when the diet is low in calcium long-term), the parathyroid gland will sense this drop and instruct the bones to demineralize a little bit and release calcium into the blood. Low vitamin D levels can also initiate bone demineralization because vitamin D increases calcium absorption in the small intestine. So, low vitamin D can lead to lower calcium levels, and that means losing more calcium out of bones to maintain that all-important blood calcium ratio. This is okay now and then, but if it happens regularly, it can lead to the loss of a significant amount of bone density over the years, which can contribute to osteoporosis if left unchecked. On the flip side, the process of increasing bone density also requires sufficient calcium, thus the push for growing children to drink plenty of milk or find other sources of dietary calcium to build strong bones and teeth.

Children, teens and young adults should especially focus on consuming enough calcium since they’re still growing and laying down bone density. By our thirties, we’ve reached peak bone mineral density and the focus turns to maintaining and preventing bone loss.

Warding off osteoporosis

Thankfully, a few tools help in this quest. First, getting enough calcium from food (1,000 mg/day for women through age 50 and men through age 70, and 1,200 mg/day for women over 50 and men over 70) will support blood calcium levels. Some good sources of calcium include:

  • dairy foods, including milk, cheese and yogurt
  • fortified juices and fortified non-dairy milks (check labels for calcium levels)
  • hearty greens such as kale, bok choy, collard and turnip greens
  • canned fish with bones, such as sardines and salmon

Supporting the body’s need for vitamin D is another key to maintaining adequate calcium levels. Sufficient sun exposure is crucial for vitamin D, but keep in mind that the amount of sunlight you need to keep up your vitamin D status varies with where you live. Vitamin D is also found in a small number of foods and is available in vitamin D supplements. Also know that nutrition is just part of the equation for building and maintaining strong bones; regular weight-bearing exercise and avoiding smoking significantly contribute to bone health, too.

What about supplements?

Taking in our nutrients from food is generally the most ideal route, so look to fresh, whole foods first for your needs. Then, if it’s right for you, use supplements to fill any gaps. (Also, always talk to a licensed health professional before beginning a new supplementation regimen, especially in the case of minerals like calcium.) Calcium supplements are often considered by people who are at a higher risk of calcium deficiency, e.g., older adults, people with a history of smoking and vegans.

Dosage is an important thing to consider any time you’re taking supplements. It’s nearly impossible to exceed the recommended amount of calcium through food sources, but the same is not true for supplements, and taking too much calcium can actually lead to problems like kidney dysfunction and calcification of soft tissues.

Absorption is another issue: the human body won’t absorb more than about 500 mg of calcium at one time, so split up the doses by several hours if taking more than that per day by supplement. Also, be aware that iron, magnesium and zinc compete with calcium for absorption in the gut, so people who are deficient in these nutrients should take calcium supplements before or between meals to avoid any issues with those other minerals. One caveat is that calcium carbonate, one of the most common forms on the market, should actually be taken with food since it requires sufficient stomach acid for absorption. Calcium citrate, the other most common form, can be taken without food and is ideal for people with low stomach acid, IBS or other related conditions.

Research results

Since calcium is clearly so important for bone health, shouldn’t it make sense that daily calcium supplementation would keep our bones strong well into older adulthood? Unfortunately, it isn’t that simple. There is conflicting research on whether calcium supplementation provides any significant health benefits, e.g., decreasing the rate of fractures, an important measure of bone health.

Some well-regarded studies have shown that daily calcium supplementation, usually along with vitamin D supplementation, reduces fracture rates, prevents loss of bone mass, and/or supports bone mineral density in vulnerable populations. On the other hand, other equally well-constructed studies have shown that calcium supplementation fails to confer any significant benefits for bone health, and some have even shown associations between calcium supplementation and negative health consequences such as kidney stones, GI distress, cardiovascular disease and heart attacks.

Overall, the bulk of the research suggests that combined calcium and vitamin D supplementation may help slow the rate of bone mineral density loss in older adults but doesn’t seem to do much for preventing fractures. We would expect more definitive research in the future, though, and wouldn’t consider that the last word.


Look for regular Sound Consumer articles over the next year from Delaney Sump, a student in the Master of Science in Nutrition/Didactic Program in Dietetics program at Bastyr University, working with Maribeth Evezich, MS, RDN, CD, an assistant professor in the Department of Nutrition and Exercise Science.

A pioneer in natural medicine, Bastyr University is a nonprofit, private university that is at the forefront of developing leaders in natural health arts and sciences for the 21st century. Bastyr offers graduate and undergraduate degrees in science-based natural medicine that integrates mind, body, spirit and nature. The University is also a leader in conducting cutting-edge research in complementary and alternative medicine and in offering affordable natural healthcare services in its local communities.

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