Have you ever been told to take a calcium supplement by a healthcare provider, only to be overwhelmed by the number of options available in stores and online? Calcium carbonate and citrate dominate the marketplace, but what about others, such as calcium hydroxyapatite, gluconate, lactate, or ones derived from algae?
Choosing the “right” calcium supplement depends on a few variables, including whether or not you will be taking it with food, how much you want to spend, how big a pill you can comfortably swallow, and how many doses (whether by pills, tablets, capsules, soft gels, powders, soft chews, or gummies) you’re willing to take at one time.
Why take calcium to begin with?
This mineral, the most abundant one in the human body, is nearly all stored in the skeleton and teeth and contributes to their structural strength. The rest (about 1 percent) is found in blood, extracellular fluid, and other tissues, where it helps the body send and receive nerve signals, maintain a normal heartbeat, release hormones, and clot blood, among other functions. If dietary intake from food or supplements is inadequate, calcium is drawn from bone to enable these vital jobs. Chronically low intake of calcium, or malabsorption due to conditions such as celiac disease, can lead to decreased bone density and an increased risk of fracture.
It’s all elemental
Calcium supplements exist as compounds of elemental calcium (the actual amount of calcium available) and a partner substance; examples are calcium carbonate and calcium gluconate. With that in mind, the first and most important step when purchasing a calcium supplement is determining how much elemental calcium it contains.
The Supplement Facts label makes this clear, indicating the number of milligrams (mg) of calcium per serving, along with the % Daily Value (%DV) for calcium, which represents how much of the daily recommended amount of elemental calcium a serving provides for adults and children 4 years or older. For instance, a product that provides 650 mg of elemental calcium per serving meets 50% of the Daily Value because the DV for calcium is 1,300 mg.
NOTE: The DV is different from the RDA (Recommended Dietary Allowance), which is not used on food or supplement labels and instead provides a range for calcium that takes into account a person’s age, gender, and pregnancy or lactation status.
Here’s a rundown on some of the more popular types of calcium supplements.
Calcium carbonate
Calcium carbonate supplements contain the highest percentage (40%) of elemental calcium and tend to be the least expensive—good features for people who want to take fewer pills as well as those on a budget. Because this form of calcium requires an acidic environment to be broken down and absorbed, calcium carbonate supplements should be taken with food, which stimulates the production of stomach acid.
Along these lines, people who do not produce enough stomach acid, or who take acid-blocking drugs such as proton pump inhibitors (PPIs), are typically advised to choose other calcium supplements that can be absorbed without the aid of stomach acid. Another downside to calcium carbonate is that it is associated with a higher prevalence of gastrointestinal side effects, such as constipation, bloating, and flatulence, compared to some other types of calcium.
A typical dose of calcium carbonate needed to reach the DV for calcium is two pills a day. Calcium carbonate is often sourced from limestone, but you can also find products made from coral, eggshell, or oyster shell calcium.
Calcium citrate
Calcium citrate—typically derived from a reaction between a source of calcium and citric acid—breaks down without the aid of stomach acid, making it a good choice for people with low gastric acid output as well as those who take a PPI or want to take their calcium on an empty stomach. Calcium citrate is also less likely to cause gastrointestinal side effects than calcium carbonate.
On the downside, calcium citrate is generally more expensive and contains less elemental calcium (21%) than the carbonate form, thus requiring more (or bigger) pills to achieve the same amount of elemental calcium per serving. For instance, four pills are typically needed to reach the DV for calcium.
Calcium gluconate and calcium lactate
These contain 9% and 13% elemental calcium, respectively, making them less practical for people who prefer not to take a handful of pills to achieve their desired dose of this mineral. Calcium gluconate is made from gluconic acid, an oxidized form of glucose, while calcium lactate is a calcium salt of lactic acid (no relation to dairy lactose).
One calcium gluconate preparation found online required six pills to provide 240 mg of elemental calcium (about 18% of the DV for calcium), while one calcium lactate product contained a mere 255 mg of elemental calcium (20% of the DV) in three large tablets, and another had only 336 mg (26% of the DV) in four large tablets.
Calcium hydroxyapatite
Typically sold as microcrystalline hydroxyapatite (MCH), calcium hydroxyapatite is usually derived from cow bones and, as such, contains magnesium, phosphorus, iron, collagen, and other components of bone. Purveyors of MCH supplements use these attributes as a selling point for their products, but quality research is lacking, and at least one manufacturer got into trouble with the Federal Trade Commission some years ago for making claims that “have not been proven by scientific research, including clinical tests, scientific papers and/or scientific studies.”
About 15 years after that FTC violation, a randomized controlled trial in the British Journal of Nutrition that lasted three months and included 100 postmenopausal women showed that MCH slowed bone turnover (a desired outcome) similarly to calcium carbonate and calcium citrate—both of which are generally far less expensive than MCH.
Calcium from algae
Calcium supplements derived from seaweed are a pricey and heavily hyped addition to the crowded marketplace. The manufacturer of AlgaeCal, for instance, maintains that its product is the “only calcium supplement clinically supported to stop bone loss and increase bone density.” Unfortunately, the modest gains in bone mineral density that were reported came from just three manufacturer-funded studies that failed to include a placebo group or comparison to other types of calcium supplements.
Furthermore, the study participants took AlgaeCal supplements that contained multiple other nutrients (such as magnesium, vitamins D and K, boron, and strontium) and were encouraged to increase activity levels—factors that make it impossible to tease out how much of an effect was from the calcium in the product.
In short, unless the company can back up its claims with well-designed published studies, you may want to hold onto the $59 it costs to purchase a one-month supply of its products.
BOTTOM LINE: Until there’s more convincing evidence for the superiority of calcium supplements other than calcium carbonate or citrate, you may just want to stick with one of those and focus on maximizing its effectiveness and safety by adhering to the tips outlined in the box below. That is, there’s no need to spend more on “fancy” calcium supplements—a 30-day supply of calcium carbonate or citrate should cost you only about $10 a month.
- Don’t take more than 500 milligrams of calcium at a time, and wait 4 to 6 hours between doses. This helps you absorb the mineral more efficiently.
- Calcium is dependent on vitamin D for absorption, so make sure your blood levels of this vitamin are sufficient. Your doctor can order a blood test of your vitamin D level and, if it’s low, may recommend a vitamin D supplement.
- If your diet already contains sources of calcium—such as dairy foods, canned salmon and sardines (with bones), tofu (processed with calcium), kale and collard greens, and fortified products—you will already be meeting some of your daily calcium needs and thus do not need to get the full Daily Value (DV) of calcium from a supplement. For instance, if you consume one 5-ounce container of Greek yogurt (providing 15% of the DV for calcium) and a cup of calcium-fortified oat milk (35%) on one day, you’re already halfway to your daily calcium goal and so only need to get the other 50% from a supplement.
- Do not consume (from food or supplements) more than the Tolerable Upper Intake Level (UL) for calcium (which is 2,000 mg a day for men and women over age 50). This limit could be especially easily reached by people who take a lot of calcium-containing antacids.
- If you are vegetarian or vegan, be aware that some supplements—notably those containing calcium hydroxyapatite—are derived from animal products; if you’re not sure of the source, you can try contacting the company. Many supplements are also made with animal-derived gelatin.
- Calcium (as well as other minerals) can be contaminated with heavy metals such as lead, so choose products that have been tested for purity by independent entities such as the U.S. Pharmacopeia (USP) or Consumerlab.com.
- If you take medications or other supplements, ask your doctor or pharmacist if they interact with calcium supplements. Those that do include iron supplements, thyroid medications, thiazide diuretics, and certain antibiotics.
