Calcium carbonate may strengthen bones, prevent colon cancer and fatty liver, and maintain normal blood pressure. Some people use it for acid reflux. But are there any side effects? And do you know how much you need? Read on to learn about the ups and downs of the most popular calcium supplement in the world.

What is Calcium Carbonate?

Calcium carbonate is found throughout the world. The forces of nature produce it from the sediment of shells and other fossils over millions of years, the most famous example being limestone. It also builds seashells and eggshells. The average eggshell contains about 2.2 g of calcium carbonate! [1, 2]

Calcium carbonate is made of calcium, oxygen, and carbon. Calcium, being the most abundant mineral in the human body, accounts for 1-2% of your body weight. But only around 1% of your total body calcium is found in the blood, while the remaining 99% is stored in your bones and teeth.

Every cell in your body needs calcium to work. This essential mineral supports your bones, heart, muscles, and nervous system [3, 4].

Calcium is formulated into various salts in supplements. These all contain different amounts of pure or elemental calcium.

Among the various forms of calcium salts added to supplements, calcium carbonate is the most common. It contains 40% elemental calcium, the highest of any form. On the downside, its absorption rate is relatively low: only around 22%. It is also the least water-soluble calcium salt, making it difficult to use in drinks [5].

People with low stomach acid will have trouble absorbing calcium carbonate, which needs an acidic environment to dissolve. If you take drugs for acid reflux, you are probably one of them (such as histamine-2 blockers and proton-pump inhibitors) [6, 7].

Snapshot

PROS

  • Cheapest calcium form
  • Works as an antacid
  • Strengthens bones & reduces fractures
  • May aid colon cancer prevention
  • Helps maintain normal blood pressure
  • May improve fatty liver disease
  • May prevent pregnancy complications
  • Relieves PMS

CONS

  • Intake needs to be balanced with other nutrients
  • Not beneficial for everyone
  • Possibly unsafe along with high-calcium diets
  • Increases the risk of kidney stones
  • May increase the risk of prostate cancer
  • May cause stomach upset
  • Inhibits iron absorption when taken with meals
  • Some products are contaminated with lead

Benefits and Uses of Calcium Carbonate

1) Strengthens Bones and Reduces Fracture Risk

Vulnerable Populations

Calcium supplements reduce the risk of fractures when taken with vitamin D. This is the conclusion of the largest review of evidence to-date. The review was carried out by a group of experts, including the International Foundation for Osteoporosis. The reduction in fracture risk was modest but significant [8].

Supplements most effectively reduce fractures in groups at high risk of calcium and vitamin D deficiency. This includes the elderly (over 50 years), menopausal women, and those being treated for osteoporosis [8].

Intense Exercise

Some evidence suggests calcium can improve bone health in physically active people, including athletes, military personnel, and manual workers.

During intense exercise, blood pH levels drop as lactate levels rise. To compensate, the body releases calcium from bones, which increases bone loss if the demand for calcium isn’t met. Calcium supplements might be helpful during these periods of intense strain on the whole body and skeletal system [9, 10].

In one trial with 243 army personnel, calcium and vitamin D improved bone density (BMD) and strength [11].

In yet another trial, 32 well-trained female athletes were given a meal with ~1350 mg calcium 90 minutes before strenuous exercise. Calcium reduced the typical bone loss seen with prolonged high-intensity exercise [9].

Healthy People

In another study with 867 healthy men, calcium with vitamin D also improved BMD, especially in the neck, hips, and spine. However, a large review concluded that more evidence is needed before we can claim that supplementation is beneficial for all non-deficient, healthy, older men [12].

The Role of Vitamin D

Vitamin D helps absorb calcium in the gut, maintain calcium levels in the blood, and strengthen the mineral composition of the bones. If you get enough sun and dietary sources year-round, you probably don’t need to supplement with vitamin D [13, 13, 14].

In sum, calcium supplements strengthen the bones and reduce fractures in people at risk of deficiency, and they might protect the bones of vigorously-active healthy people.

2) Reduces the Risk of Falls in the Elderly

A review study of more than 16,000 elderly people found that a combination of calcium and vitamin D supplements reduces the risk of falls. Falls are a huge hazard for the elderly and often lead to serious or even fatal fractures [15].

There is no doubt that adequate vitamin D and calcium balance is important for bone and overall health in the elderly. Together, these nutrients help maintain normal posture and muscle-nerve communication [16].

But some findings about their combination in supplements are less conclusive, with a number of studies failing to find any benefit [16].

All in all, vitamin D-calcium supplements might improve posture and lower the risk of falls in the elderly. Their combination is safe and cheap, but more research is needed to determine how well it works.

3) May Help Prevent Colon Cancer

According to several review studies, calcium supplements may help prevent colon cancer or reduce the risk of it coming back. Most of the trials found that calcium supplements were more effective when taken with vitamin D at the same time [17, 18, 19, 20].

Most of the studies, however, didn’t take dietary and lifestyle factors into consideration. These can have a huge impact on colon cancer risk; they modify the gut flora and eventually affect the balance between health and disease [21].

Calcium supplements aid in colon cancer prevention by protecting cells in the colon lining from the damaging effects of free bile and fatty acids. Another way calcium might work is by activating a pathway called APC/beta-catenin, which becomes underactive early in colon cancer. Vitamin D, in turn, helps break down bile acids and enhances DNA repair [22, 23].

All in all, getting sufficient amounts of calcium from food or supplements and keeping your vitamin D levels in check might reduce your risk of colon cancer.

4) Maintains Normal Blood Pressure

Adequate calcium intake helps maintain normal blood pressure. It might prevent the onset of high blood pressure, according to a large review on over 3k healthy people. Calcium intake slightly reduced blood pressure, especially in those under 35 years of age. The benefits depended on the dose: 1,000 to 1,500 mg dropped blood pressure around 1 point, and over 1,500 mg almost 3 points [24]:

5) May Improve Fatty Liver Disease

Vitamin D deficiency is common in people with liver disease. Low vitamin D status eventually reduces calcium absorption and can lead to bone diseases [25].

In two trial of 120 people with nonalcoholic fatty liver disease, calcium and vitamin D improved several markers of liver damage and heart health (ALT, AST, triglycerides, and LDL cholesterol). Vitamin D alone did not improve liver health [26, 27].

These findings highlight the tight synergy between calcium and vitamin D and their importance for liver, bone, and heart health.

6) Reduces the Risk of Pregnancy Complications

Preeclampsia is sudden high blood pressure during pregnancy, which usually starts around the 20th week. It affects about 5% of pregnant women and can lead to organ damage, pregnancy complications, and even death if left untreated. Adequate calcium intake is an important part of prevention [28].

According to a large review, calcium supplements (over 1g/day) cut the risk of preeclampsia in half [29].

Supplementation is particularly important if you don’t get enough calcium from food. The World Health Organization recommends 1.5-2 g/day for pregnant women with low dietary calcium intake. Consult your doctor before supplementing to rule out any risks or interactions [30].

7) Relieves PMS

Premenstrual syndrome (PMS) is extremely common and the exact causes are diverse. According to several clinical trials with women suffering from PMS, calcium supplements can relieve many of the symptoms of PMS. Supplementation helped with PMS-related anxiety, depression, fatigue, and water retention [31, 32, 33, 34].

8) May Reduce Inflammation

In clinical trials, calcium reduced several markers of inflammation, including IL-1, IL-6, IL-8, TNF-alpha, and C-reactive protein (CRP). Additionally, adequate levels of this mineral can boost the master antioxidant glutathione in cells [35, 36, 37, 38, 39].

However, supplementing is not always a good idea. The causes of inflammation are extremely diverse and calcium can do more harm than good in certain cases. For example, people with rheumatoid arthritis taking calcium supplements were more likely to die (from any cause or heart disease), based on the results of a recent Norweigan analysis [40].

9) Supports Weight Loss

A clinical trial of 53 people found that calcium and vitamin D increased weight loss when combined with a restricted diet. The doses used were 600 mg calcium and 125 IU vitamin daily [41].

However, a recent review of 41 studies concluded that calcium supplements don’t increase weight loss [41].

10) Relieves Acid Reflux

Calcium carbonate is a popular remedy for indigestion, heartburn and acid reflux. Most people know it as Tums, Rolaids, and Chooz. Being alkaline, calcium carbonate neutralizes stomach acid. One study revealed that it also helps clear acid from the esophagus (food pipe) [42, 43].

Its ability to neutralize stomach acid doesn’t last long, though. Compared to a histamine-2 antagonist (famotidine/Pepcid), calcium carbonate only worked for 60 mins, while famotidine lasted for 9 hours [44].

Calcium carbonate doesn’t affect the amount of stomach acid you release after a meal, as confirmed in one clinical trial [45].

If your reflux is mild or temporary, calcium carbonate may help. But if you have chronic reflux and indigestion, long-term antacid use is not a good idea. Many nutrients depend on stomach acid for absorption. Continually lowering your stomach acid can lead to nutrient deficiencies in the long run [46, 47].

Another issue with low stomach acid is bacterial overgrowth in the gut. Stomach acid is our first line of defense against food- or waterborne infections. When stomach acid gets too low, it can no longer protect us against bacteria. Bacteria can then sneak into the intestines, causing an array of problems [48, 49].

Instead of relying on antacids, look into the causes of your acid reflux instead. In many cases, acid reflux can be improved or eliminated with simple lifestyle changes. This includes avoiding trigger foods (e.g. salted and fatty foods, chocolate, fizzy drinks), exercise, and raising the head of your bed [50, 51].

You may also want to look into herbal bitters and digestive enzymes as additional remedies that might help with indigestion and acid reflux.

To sum it up, calcium carbonate may relieve the symptoms of acid reflux temporarily, but it might do more harm than good in the long run.

Limitations and Caveats

Some studies suggest calcium supplements carries health risks and doesn’t reduce fracture risk. Experts are still debating whether calcium supplements are helpful or if dietary intake is the only way to go. On top of that, many studies fail to take co-factors such as magnesium or vitamin K2 into account.

Future research has yet to clear the conflicting findings about calcium supplements.

Calcium Carbonate Side Effects

Risk of Kidney Stones

The most well-known side effect of calcium supplements is a modestly increased risk of kidney stones. Data from studies suggest around 17% increased risk. The chance of this happening may be reduced by using the calcium citrate form. Calcium citrate reduces the formation and growth of the most common kidney stones (oxalic acid) [8, 52].

Gut Issues

Another relatively common side effect of calcium supplements is stomach upset. Symptoms may include constipation, cramping and bloating. Heartburn and nausea are also possible. Calcium carbonate is most likely to cause these problems, as it requires stomach acid for absorption. So again, choosing the citrate form may minimize this side effect [8, 53].

Decreased Nutrient Absorption

Calcium carbonate can inhibit iron absorption when taken with meals. For women, whose needs of iron is higher than men’s, it is safer to take the calcium carbonate away from meals [54, 55].

When using calcium carbonate as an antacid, don’t take it for more than 2 weeks. Continually lowering your stomach acid may possibly lead to nutrient deficiencies and bacterial overgrowth in the long run [56, 46, 47, 48, 49].

Calcium Carbonate Safety

Heart Health

Some studies have found that calcium supplements increase the risk of heart disease. However, several large reviews consider the evidence too weak to draw any reliable conclusions.

A 2012 review of 16 studies and over 350k people didn’t find a link between heart disease and calcium supplements [57].

Two more recent reviews similarly found no evidence of increased risk of heart disease, concluding that calcium intake from all sources below 2,500 mg/day is safe [58, 59].

Reviews by expert panels – including the National Osteoporosis Foundation, the American Society for Preventive Cardiology, and the International Foundation for Osteoporosis – back up this opinion [60, 8].

Prostate Cancer

There have been some concerns that high calcium intakes in men may increase their risk of prostate cancer. Research on this is not consistent, however.

A review study including more than 900k men aged 50-70 years found that high calcium intake does increase the risk of prostate cancer. More than 750 mg a day was associated with a higher risk [61].

Other studies have found that the risk of prostate cancer only increase substantially when calcium intake is over 2,000 mg a day [62, 63].

One reason why high calcium intake may increase the risk of cancer is that it puts extra demand on vitamin D. The more calcium you take, the more vitamin D you need. Vitamin D is known to protect cells from cancer. So make sure you get enough vitamin D if you supplement calcium [64, 65].

The Dangers of Getting More than You Need

The safety and effectiveness of calcium supplements may depend on your dietary calcium intake. According to a trial with over 60k women, supplements increased the risk of death only in those who get over 1,400 mg/day from food [66].

Tolerable Upper Intake Levels (ULs) for Calcium

With calcium, more is not better. Below are the maximum daily levels of calcium you should not exceed, including both supplements and food sources. About 5% of women over the age of 50 years surpass these levels by almost 400mg/day [3].

Going over the upper tolerable levels for a short while is unlikely to cause any issues, but doing so long term is unsafe [3].

AgeMaleFemalePregnantLactating
0–6 months1,000 mg1,000 mg
7–12 months1,500 mg1,500 mg
1–8 years2,500 mg2,500 mg
9–18 years3,000 mg3,000 mg3,000 mg3,000 mg
19–50 years2,500 mg2,500 mg2,500 mg2,500 mg
51+ years2,000 mg2,000 mg

The Gender Effect

An observational study of more than 130k people revealed that men who supplement with over 1,000 mg of calcium per day are at an increased risk of heart disease. The same dosage did not increase the risk in women [67].

Nutrient Balance

Over-supplementing calcium may come at the expense of other nutrient deficiencies. When you increase your calcium intake, you need to ensure you are getting sufficient amounts of:

These are important nutrients help calcium work optimally in the body. If you lack any of them, you can set off a chain of imbalances in the body.

Vitamin D

The importance of vitamin D status in people taking calcium supplements cannot be overstated.

We have already seen that vitamin D and calcium work in close synergy. Vitamin D maintains calcium blood levels, increases calcium absorption, and works together with calcium to enhance bone, muscle, and heart health. They were used in combination in most studies [68, 69].

Make sure to maintain your vitamin D levels through regular sun exposure and adequate dietary sources. Alternatively, consider supplementing.

Magnesium

Magnesium maintains calcium blood levels and is needed for the production and activation of vitamin D. The ratio of calcium to magnesium in your food or supplements is much more important than the dosage of each [70].

According to conventional advice, the optimal ratio is likely 2:1, which would mean you need twice as much calcium as magnesium. Shifting this balance slightly up (to 2.6:1) or down (to 1.7:1) might have detrimental health consequences [70+].

But it seems like most Americans are getting 3 times the amount of calcium to magnesium (3:1 ratio) – just from food [70+]!

Researchers speculate the relative abundance of calcium at the expense of magnesium in modern diets is driving many chronic health problems – from diabetes to heart and bone diseases.

Bottom line?
Assure you’re getting enough magnesium relative to calcium from both supplements and foods.

Vitamin K2

Vitamin K2 helps calcium build bones while preventing the buildup of calcium in blood vessels and soft tissues (calcification). But the typical Western diet is low in this vitamin! Increasing vitamin K2 intake may reduce many health risks linked to calcium supplementation [71, 72].

Many forms of Vitamin K2 exist, but the MK-7 form, in particular, increases bone strength and reduces artery hardening [73, 74].

Increase your vitamin K2 intake if you’re taking calcium supplements. Some good vitamin K2 food sources are dairy and fat from grass-fed animals, egg yolks, organ meats, and fermented foods [75, 76, 77].

Heavy Metal Contamination

Calcium supplements may be contaminated with heavy metals. Analyses discovered lead levels above the safe limits in some products. The “natural sources” of calcium (dolomite, coral calcium, oyster shell) contained the highest levels of lead: 4-12x that of refined supplements! [78, 79, 80]

Drug Interactions

Talk to your doctor before supplementing if you take any prescription medication to rule out dangerous interactions. Because calcium carbonate can reduce absorption, don’t take it within 1-2 hours of any medications. Be particularly careful with these medications [56, 81]:

  • Ceftriaxone: can result in life-threatening damage to the lungs and kidneys
  • Antacids (TUMS, Rolaids, Chooz): combining these may lead to an overdose of calcium
  • Dolutegravir, Elvitegravir
  • Digoxin (Lanoxin)
  • Etidronate (Didronel)
  • Phenytoin (Dilantin)
  • Tetracycline (Sumycin)
Calcium supplements are likely safe if you don’t exceed the maximum recommended levels and get sufficient amounts of other important nutrients. If you are already eating plenty of calcium-rich foods (providing over 1,400 mg/day), supplementing is unnecessary and may increase your risk of heart disease.

Calcium Dosage

Daily Needs

Most adults need at least 1,000 mg of calcium per day. Women over 50 years need a bit more: 1,200 mg a day. Teenagers, pregnant and nursing women should aim for at least 1,300 mg calcium per day [3].

The amount of supplemental calcium you need depends on your diet. If your dietary intake is low, you can supplement with up to 1,000 mg/day, unless directed differently by a doctor. Divided doses of no more than 500 mg work best [82].

Aim to get 1,000-1,400 mg of calcium per day from both food and supplements.

Clinical Dosage

The average daily calcium doses in clinical trials were as follows:

  • Bone health: 1,000 to 1,200 mg
  • Colon cancer: 1,200 to 2,000 mg
  • Fatty liver disease: 500 mg
  • Blood pressure: 1,000 to 1,500 mg
  • Preeclampsia: 1,000 mg
  • PMS: 1,000 to 1,200 mg
  • Inflammation: 1,000 mg

This puts the typical calcium dosage in a range between 1,000 and 1,200 mg/day.

For acid reflux and indigestion, it’s recommended to take 2-4 tablets of Tums per day, as needed (containing 750-1,000 mg of calcium carbonate per tablet).

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Takeaway

Calcium carbonate may strengthen bones, reduce the risk of colon cancer, and improve fatty liver disease. It can also relieve heartburn.

On the downside, it can cause stomach upset and kidney stones. Conflicting evidence linked its use to health risks, most of which can be avoided by getting sufficient amounts of other nutrients (vitamin D, magnesium and vitamin K).

If you’re eating plenty of calcium-rich foods, you should not supplement. Going over the maximum tolerable intake can harm your health.

Taking calcium carbonate for indigestion and acid reflux may do more harm than good in the long run. Look to solve the underlying cause of your digestion issues instead.

About the Author

Jimmy Julajak, MSc

MS (Psychology)

Jimmy got his MSc from the University of Copenhagen.

Jimmy is a psychologist and researcher. He is particularly interested in the workings of the brain and strategies for improving brain health. He believes that people shouldn't hand over the responsibility for their health only to their doctors. His aim is to empower each person with easy-to-understand, science-based health knowledge.

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