6 Reasons Taking Calcium Supplements Could Be Harmful

calcium supplements

Calcium is an essential mineral that your body needs in relatively large quantities, unlike trace minerals, like iron, that your body needs only in tiny amounts. 99% of the calcium you take in is stored in your bones and teeth. You need the other 1% on a minute-by-minute basis to sustain life. For example, calcium plays a key role in muscle contractions and the contractions of your heart. Plus, it’s a signaling molecule that tells cells what to do. So, the calcium in your bloodstream is every bit as important or more important than the 99% of calcium that’s in your bones. If it drops too high or too low, it can kill you.

Due to the essential nature of calcium, taking calcium supplements is popular, especially among women. Most people take them on the premise that supplemental calcium improves bone health. Yet, recent studies show that calcium supplements don’t substantially boost bone density or prevent fractures in pre-menopausal women. In addition, calcium has only modest benefits for bone density in post-menopausal women.  But the word hasn’t gotten out as people continue to take them. What’s more, taking a calcium supplement is harmful. Here are six reasons you should think before popping a calcium supplement.

Cardiovascular Risk

A randomized controlled study of over 100 participants linked calcium supplements with a 30% higher risk of heart attacks. This is an increase in relative risk, so it’s not a huge increase in absolute terms but it does raise red flags about the safety of supplemental calcium. If calcium supplements don’t reduce fracture risk or significantly improve bone density, why take them and incur even a small risk?

Plus, there’s a plausible mechanism by which this might occur. Calcium, in supplement form, may deposit in the inner walls of arteries and contribute to plaque formation. Studies are equivocal at the moment, so we need more research to say with certainty if calcium pills and tablets are harmful to heart health.

Fortunately, there doesn’t seem to be a higher risk of heart disease in people who consume greater quantities of dietary calcium. But it’s important to weigh the risk to benefit ratio. If you can’t get enough calcium through diet, a supplement may still be necessary. Discuss this with your physician.

Bad For Brain Health?

Recently, an observational study found that older women who took calcium supplements over a 5-year period had a slightly greater risk of developing dementia. The study involved 700 women and was observational, so it’s hard to say whether the calcium supplements were the cause. It’s possible that some other factor common to people who take calcium supplements and have dementia explains the findings. The women who developed dementia also had a history of stroke. It’s not clear whether the same applies to women who haven’t had a stroke. The researchers also didn’t see a link between calcium pills and tablets and dementia in men. It’s too early to say calcium supplements cause dementia, but it would be nice to see more research, including randomized clinical trials.

A Higher Risk of Kidney Stones

If you have a history of kidney stones, take calcium supplements with caution. Most kidney stones are made of calcium oxalate. Studies show that calcium supplements increase the risk of forming calcium oxalate stones while dietary calcium does not. So, food is the best source of calcium if you have a history of kidney stones.

It’s not clear why supplements increase kidney stone risk, but diet doesn’t. One theory is that dietary calcium binds to the oxalates in foods and helps them travel out of the body via the digestive tract. In contrast, people often take calcium tablets on an empty stomach, so there’s no oxalate-containing food in the stomach to bind to the calcium and take the calcium out of the body. So, the calcium ends up in the kidneys where it can cause kidney stones.

The good news is dietary calcium doesn’t increase the risk and may reduce it. To further lower the odds of developing kidney stones, drink more water and add lemon. The citric acid in lemon helps prevent kidney stones from forming. If you take a calcium supplement, take it with food and choose calcium citrate, as it’s similar to citric acid.

A Greater Risk of Pre-Malignant Colon Polyps

Here’s more disturbing news. Recent research suggests that calcium supplements increase the risk of pre-malignant colon polyps. A study published in the British Medical Journal found that participants who took 1200 mg of calcium daily had a higher incidence of serrated colon polyps. Polyps come in various types, some of which are unlikely to become cancer. But serrated polyps carry a high risk of developing into colon cancer and are more concerning. The increased incidence showed up between 6 to 10 years after the participants started swallowing calcium supplements. Taking calcium and vitamin D supplements (1,000 mg daily) together was also linked with a higher risk of serrated colon polyps, although vitamin d supplements alone were not. Colon cancer is the second leading cause of cancer death in the United States.


Constipation isn’t life or death but it’s uncomfortable. Constipation is a common side effect with calcium supplements. If you take a calcium supplement, calcium carbonate is the least constipating. Some people also experience bloating when they take calcium supplements.

Calcium Supplements May Reduce the Absorption of Some Medications

If you take a calcium supplement, don’t take it around the time you take other medications. Calcium supplements can interfere with some medications, including thyroid supplementation, anti-seizure medications, bisphosphonates (for osteoporosis), diuretics, prednisone, antacids, and some antibiotics. It’s another reason to think about the supplements you take and how they interact with each other and with medications.


The Bottom Line

The health benefits vs risks of calcium supplements are unclear. Try to get your calcium from food sources rather than supplements. However, there may be situations where you need a calcium supplement. Discuss this with your physician.



ScienceBasedMedicine.com. “Are guidelines for calcium and vitamin D rooted in evidence, or vested interests?”

AJMC.com. “Who Should Take Calcium Supplements?”

ScienceBasedMedicine.com. “Do calcium supplements cause heart attacks?”

BMJ 2010;341:c3691.
Neurology. 2016 Oct 18; 87(16): 1674–1680.
WebMD.com. “Calcium Supplements Tied to Kidney Stone Risk”
Gut Published Online First: 01 March 2018. doi: 10.1136/gutjnl-2017-315242.
Mayo Clinic. “Calcium and calcium supplements: Achieving the right balance”
National Institutes of Health. “Calcium”


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