Calcium Benefits, Safety, and Side Effects

Calcium is an essential mineral that is primarily associated with bone health. However, it has a range of other crucial functions within the body. Therefore, a growing number of people are considering taking calcium tablets to boost their intake.

Calcium supplements are especially popular among older women who are concerned about osteoporosis. But recent research suggests that high doses of calcium could increase the risk of heart disease. So, do the benefits outweigh the dangers?

We delve into the science behind calcium and explain whether taking a supplement is a good idea. Here’s all you need to know.

What Is Calcium?

Calcium is a soft metal with a silvery appearance. It is the fifth most abundant element in the Earth’s crust, although it does not occur naturally in its free state. Instead, it binds with other elements to form compounds such as lime (calcium oxide) and calcite (calcium carbonate).

Furthermore, calcium is the most abundant mineral in the human body. The average adult female contains around 1.2g, while the average adult male contains around 1.4g.


The vast majority of calcium (approximately 99%) is stored in the bones and teeth in a form known as hydroxyapatite. Hydroxyapatite is a mixture of calcium and phosphorus.

Calcium plays a vital role in maintaining bone health and has many other essential physiological functions. Let’s look at how this mineral works and its health benefits.

How Does Calcium Work?

As well as keeping the skeleton strong and healthy, calcium is involved in the following processes:

  • Muscle function
  • Blood vessel contraction and dilation
  • Blood clotting
  • Nerve signaling
  • Hormone secretion

The bones undergo constant remodeling to ensure the body has enough calcium for these functions. The process is controlled by two hormones called parathyroid hormone (PTH) and calcitonin.

If calcium levels in the blood fall too low, the parathyroid gland secretes PTH, which tells the bones to release more calcium. It also reduces the amount of calcium the kidneys excrete in urine.

When calcium levels in the blood are sufficient, the thyroid gland secretes calcitonin, which tells the bones to hold on to calcium. It also increases the amount of calcium excreted in the urine if levels become too high.

When the bones release calcium, the process is known as “resorption” When they accumulate calcium, it is known as “formation.” Because bone resorption and formation are constantly happening, the entire skeleton is replaced approximately every 10 years.

However, the resorption rate can overtake formation with age, leading to bone weakness. This phenomenon is especially pronounced in menopausal women due to declining estrogen levels.

People also absorb less calcium from food as they age, meaning it can be challenging to get enough daily. Therefore, many older adults consider taking a calcium supplement. But is it beneficial?

Calcium Benefits

The benefits of calcium for human health are numerous. We have explored some of the best-studied examples below.

Bone Health

Calcium is known for its critical role in bone health, and many people take supplements to try and prevent osteoporosis.

Osteoporosis weakens the bones and can increase the risk of falls and fractures. Hip, spine, and wrist fractures are the most common, with hip fractures being a major cause of disability among older adults.

When doctors test for osteoporosis, they check a measure known as bone mineral density (BMD). It indicates the amounts of calcium and other minerals in the bones. Having a lower BMD is associated with an increased risk of osteoporosis.

Unfortunately, the evidence regarding calcium intake and BMD is mixed. Some studies have had positive results, while others have found no clear association between calcium consumption, bone health, and fracture risk.

For instance, a 2015 meta-analysis included 15 studies on dietary calcium and 51 studies on calcium supplementation. The researchers found that calcium had a slight positive effect on BMD. However, the effects were non-progressive (i.e., improvements plateaued after one year), and the benefits were too small to impact fracture risk.

Moreover, the US Preventative Services Task Force has concluded, with moderate to high certainty, that daily calcium doses under 1000mg do not prevent fractures in postmenopausal women. The evidence on higher doses is insufficient. Therefore, it does not recommend using calcium supplements for this purpose.

That said, it is important to consume enough calcium from dietary sources (see below) to maintain bone health. Other minerals, such as magnesium, silicon, and boron, are also essential, as are vitamins D and K, which aid calcium absorption. Regular weight-bearing exercise, reducing alcohol consumption, and not smoking can also help to strengthen the bones.

Cancer Prevention

There has been some research into whether calcium can prevent certain forms of cancer. Again, the evidence is mixed, although it seems the mineral could reduce the risk of developing colorectal cancer.

According to the National Cancer Institute, calcium supplementation of up to 1200mg daily modestly reduces the risk of colorectal cancer. It seems that the mineral could bind to acids that damage cells in the gut. It may also inhibit the growth of cancerous cells and improve cell signaling that causes cancer cells to die.

However, the institute does not recommend using calcium for cancer prevention due to a lack of robust evidence. It also appears that calcium could increase the risk of prostate cancer in men, although this may only relate to calcium from dairy products.

Far more research is required before we fully understand the relationship between calcium and cancer.

Cardiovascular Disease

Calcium has been linked to improved cardiovascular health and a reduced risk of heart disease.

There is an association between low calcium intake and high blood pressure, strokes, and clogged arteries. It also appears that calcium supplements could reduce blood pressure and the risk of preeclampsia (high blood pressure during pregnancy).

One way calcium could benefit heart health is by binding fatty acids in the gut to reduce their absorption.

However, there is also mounting evidence that high-dose calcium supplements could increase the risk of cardiovascular and coronary heart disease in healthy, postmenopausal women. Possible mechanisms include hardening the arteries and increasing the blood’s tendency to coagulate (clot).

A 2021 meta-analysis of 13 trials found a significantly increased risk of heart disease with calcium intakes of 700–1000mg daily from dietary sources and 1000mg from supplements. Therefore, increasing calcium consumption for heart health is inadvisable unless recommended to do so by a physician.

Calcium Deficiency

People who do not consume enough calcium could develop calcium deficiency, also known as hypocalcemia. Mild cases may not cause any symptoms, but more severe hypocalcemia can lead to:

  • Muscle cramps, spasms, and weakness
  • Numbness or tingling in the hands and feet
  • Irregular heartbeat
  • Poor appetite
  • Kidney problems
  • Depression or bipolar disorder
  • Cataracts
  • Congestive heart failure
  • Seizures
  • Coma (rare)

Risk factors for developing hypocalcemia include:

  • Vitamin D or magnesium deficiency
  • Low dairy intake due to lactose intolerance or vegan diets
  • Critical illness
  • Certain medications (bisphosphonates, cisplatin, proton pump inhibitors)

People at risk of calcium deficiency should consult their healthcare provider to discuss whether a supplement may be beneficial.

Calcium Supplement Options

Calcium tablets are available in several forms. It is a common ingredient in multivitamin and mineral preparations. Products containing calcium alone or in combination with vitamin D are also popular.

Multivitamins usually contain 200–300mg of calcium per serving, while calcium or calcium plus vitamin D products usually contain 500–600mg.

Calcium supplements contain calcium salts, such as calcium carbonate or calcium citrate. Calcium carbonate contains more elemental calcium (40%) than calcium citrate (21%).

However, calcium carbonate relies on stomach acid for absorption and is best taken with food. In contrast, calcium citrate can be taken at any time and may be more suitable for people with low stomach acid levels.

Calcium carbonate is also more likely to cause side effects than calcium citrate.

Calcium Supplements: Side Effects

Possible calcium side effects include gas, bloating, and constipation. People experiencing these side effects might consider switching to a different form of calcium, taking their supplement with food, or taking smaller doses throughout the day.


As we mentioned earlier, high calcium doses could increase cardiovascular disease risk. Therefore, individuals should seek medical advice before beginning supplementation.

Furthermore, calcium can interact with other medicines, including dolutegravir, levothyroxine, lithium, and quinolone antibiotics. Supplements should not be taken at the same time as these medicines.

Calcium Dosage

The recommended dietary allowance of calcium for most adults is 1000mg daily. This increases to 1200mg daily for women over 50 and men and women over 70. These figures are based on how much of the mineral is required to maintain bone health and blood calcium levels.

Interestingly, the more calcium one consumes, the less the body absorbs. For example, with a calcium dosage of 200mg daily, 40% of the mineral is absorbed. However, with a dosage of 2000mg daily, only 15% is absorbed.

Therefore, taking more calcium is not necessarily better. The National Institutes of Health suggests that supplement doses of 500mg or less provide optimal absorption. The upper daily limit for calcium is 2500mg.

Excess calcium (hypercalcemia) is rare in healthy people but could affect individuals with cancer, hyperparathyroidism, or other medical conditions. Symptoms include:

  • Poor muscle tone
  • Kidney problems
  • Low phosphorus levels
  • Constipation
  • Weight loss
  • Fatigue
  • Excessive urination
  • Irregular heartbeat
  • Increased cardiovascular disease risk

Most experts recommend meeting one’s calcium requirements through dietary intake and only taking supplements if this is not possible.

Dietary Calcium Sources

Dairy products like milk, yogurt, and cheese are the best dietary sources of calcium. The mineral can also be found in several other foods, including:

  • Canned fish with edible bones, such as sardines
  • Leafy greens, including kale, broccoli, and bok choi
  • Calcium-set tofu
  • Almonds
  • Brazil nuts
  • Sunflower seeds
  • Tahini
  • Fortified foods and drinks

Calcium from plant-based sources may be more difficult to absorb than calcium from animal products. Therefore, vegans should discuss supplementation with a healthcare professional.

Furthermore, high-protein and high-salt diets, excessive alcohol consumption, and corticosteroid use may reduce calcium absorption or increase excretion. Therefore, these factors may increase one’s daily requirements.

Finally, adequate vitamin D intake is necessary for healthy calcium absorption. The best natural source is sunlight on the skin, although vitamin D can also be found in oily fish, liver, egg yolks, and some mushrooms.

Final Thoughts on Calcium

Calcium is essential to health, but taking a calcium supplement may not be helpful for everyone. While these products may slightly impact bone health, heart health, and cancer risk, they could also cause serious side effects.

Anyone considering supplementation should carefully weigh the benefits against the risks and consult a professional for further guidance.

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