Calcium is one of the most abundant and important minerals in the body, playing a crucial role in how we function. Not getting enough can put you at risk for weakened bones that may progress to osteoporosis over time. “If you struggle to eat enough calcium through your diet, adding a high-quality calcium supplement can help fill the gap. Without it, you risk long-term bone health as the body resorts to drawing calcium from the bones to maintain stable levels,” explains Cara Harbstreet, M.S., R.D., L.D., of Street Smart Nutrition. But what form should you take? Looking at two of the most common, you’ll have to choose between calcium citrate vs. calcium carbonate.

Meet the experts: Cara Harbstreet, M.S., R.D., L.D., of Street Smart Nutrition; Rachel Gargano, M.S., R.D., C.S.S.D., the chief registered dietitian at Live it Up.

In addition to low calcium intake, there are other factors that may cause your levels to drop. “Low levels of circulating calcium, also called hypocalcemia, can sometimes result from not getting enough vitamin D and magnesium,” says Rachel Gargano, M.S., R.D., C.S.S.D., the Chief Registered Dietitian at Live it Up. “This is because vitamin D helps the body absorb calcium, while low magnesium can impair the body’s ability to regulate blood calcium levels appropriately.” According to the Cleveland Clinic, hypocalcemia is also often caused by abnormal levels of parathyroid hormone. But taking a calcium supplement (that’s been approved by your doctor) can reverse low calcium. Here, dietitians offer advice on calcium citrate vs. calcium carbonate to help you determine which is best for you.

Benefits of calcium citrate

“Calcium citrate is basically the mineral calcium bound with citric acid,” says Gargano. One of the biggest benefits of calcium citrate is that it can be taken with or without food, because it’s not dependent on the amount of acid in the stomach to be broken down and utilized (unlike calcium carbonate, which is not absorbed as well if you have low levels of stomach acid). “This type of calcium supplement is best if you take medication to reduce stomach acid or want the flexibility and convenience of being able to take it without meals,” Harbstreet says.

Another benefit of calcium citrate is that it is less likely to increase your risk of developing kidney stones than calcium carbonate. A study in the Journal of Bone and Mineral Research compared the efficacy of calcium citrate vs. calcium carbonate for treating low parathyroid (the most common condition associated with low calcium). It found that while both forms of calcium were equally successful for improving levels of parathyroid hormone, calcium citrate was less likely to cause constipation and reduced the amount of oxalates in urine, which is associated with a lower risk of kidney stones.

Potential downsides to calcium citrate

“Calcium citrate can be more expensive compared to other calcium supplements,” says Harbstreet. Calcium citrate supplements also only contain 21% elemental calcium, according to the National Institutes of Health (NIH). “This might mean that you need to take more pills of calcium citrate to get the same amount of calcium as compared to a calcium carbonate supplement,” Gargano explains. This might end up being an issue if your healthcare provider recommends taking a higher dose of the mineral. Gargano says that the more calcium you take at once, the less of it is actually absorbed by the body. So if you’re taking a high dose of calcium citrate, you may end up needing to take multiple pills more than once a day.

Benefits of calcium carbonate

“Calcium carbonate is another form of calcium that has a wider range of uses as a food additive as well as non-food uses,” says Harbstreet. “It’s a less expensive form of calcium but is more commonly used as an antacid rather than a supplement.” Calcium carbonate is actually the active ingredient in TUMS, which is meant to relieve heartburn, indigestion, and upset stomach—but it is also used as a calcium supplement. “Interestingly, even though calcium citrate is more bioavailable in supplement form, calcium carbonate is used to fortify foods, because within the food matrix it is absorbed better,” Gargano says. That means that if you see a breakfast cereal fortified with calcium, like Cheerios, there’s a good chance it features calcium carbonate.

While calcium citrate contains a relatively low percentage of elemental calcium, calcium carbonate has double, at 40% calcium, per the NIH. So if you need to take a high dose, it may be a little easier to do so with calcium carbonate, provided that you are able to take your supplement with food. “This might be your top choice if you need a more budget-friendly option, or if you have a consistent schedule to be able to take it with meals,” Harbstreet says.

Potential downsides to calcium carbonate

“If you don’t have a lot of stomach acid, such as if you’re an older adult, calcium carbonate is not your ideal supplement option because it needs optimal acid to be absorbed,” Gargano says. It may also cause gastrointestinal side effects, Harbstreet adds. According to the National Library of Medicine, calcium carbonate can cause upset stomach, vomiting, stomach pain, belching, and constipation if you’re taking it regularly to increase your calcium levels (as opposed to taking it as needed as an antacid).

Calcium citrate vs. calcium carbonate: Which is better for you?

Both calcium citrate and calcium carbonate can increase low calcium levels, if that’s what you need. If cost isn’t an issue and you need something you can take anytime, anywhere, calcium citrate is likely a better option. But if you’re able to consistently take your calcium with a meal, calcium carbonate is a solid pick. “With either option, consult your healthcare team first,” says Harbstreet. “They can make a personalized recommendation for the form and dose that’s best for you.”

Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.

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