Calcium 101 – How to Choose the Best Calcium Supplement

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Wooden spoon of Calcium Carbonate tablets above a glass of milk

More than 2.3 million Canadians are living with osteoporosis, and many more are at risk of the condition. [1] Along with a healthy diet and regular load-bearing exercise, calcium supplements can help build and maintain strong, healthy bones.

Experts agree that the ideal way to get nutrients into your body to stay healthy is from your diet. However, some people may need help to meet the recommended daily intake (RDI) from diet alone. The RDI for calcium varies in adults from 1000 mg to 1200 mg daily. These values are a combination of diet and supplements. If your doctor recommends taking a calcium supplement, the following information may be useful.

How Much Calcium Do We Need? [2]

Age Daily Calcium Requirement
(Can be from Diet and Supplements)
19-50 1000 mg
51-70 Men 1000 mg
Women 1200 mg
>70 1200 mg
Pregnancy & Lactation 19–50 1000 mg

Are you Getting Enough Calcium?

When we don’t consume enough calcium, the body starts to borrow it from the bones and teeth. This is known as being in negative calcium balance, and, if it continues, bones and teeth can become weak over time.

Inadequate calcium intake raises the risk of bone loss, osteomalacia and osteoporosis, and fracture. Other risk factors for osteoporosis include a family history of fractures, age, sex, previous fracture, and things that affect calcium absorption and need.

You might need more calcium if you: [3]

  • Are taking glucocorticoid drugs for more than three months
  • Have Crohn’s disease or celiac disease
  • Have other medical conditions that inhibit nutrient absorption
  • Use medications that contribute to bone loss
  • Are pregnant or nursing an infant
  • Are very active (to fuel all that muscle activity!)
  • Eat a restricted diet – especially if you don’t eat dairy products, fortified foods, or lots of cruciferous vegetables

If you take any medications regularly or have concerns about calcium absorption, talk to your health care practitioner for advice.

What are the Benefits of Taking Calcium Supplements?

Taking calcium in the form of supplements, in addition to dietary calcium, helps the bones rebuild and stay strong. Calcium is required for a healthy heart, nerves, and blood-clotting systems. People commonly take calcium by mouth to treat and prevent low calcium levels, muscle cramps, osteoporosis, softening of the bones, and PMS.

What are the Forms of Calcium?

1. Calcium Carbonate

Calcium carbonate is what you’ll find in most calcium supplements and is usually derived from oyster shells or limestone. This form of calcium is inexpensive and provides 40% of elemental calcium, which is the highest level available in supplements. This means you can take fewer, smaller tablets to meet your daily needs.

Calcium carbonate is not water-soluble but readily dissolves, given enough acidity. This makes it a great choice for healthy adults with sufficient stomach acid who want to increase their calcium intake and don’t mind taking a tablet with meals. For anyone else, especially people taking antacids, a different form of the mineral may prove a better choice.

2. Calcium Citrate

Calcium citrate is another form of supplemental calcium and is much better absorbed than calcium carbonate. It can be taken with or without food as it is a water-soluble (does not require stomach acid to break down), acid-based compound created by reacting calcium carbonate with citric acid from citrus fruits.

Calcium citrate is a great choice for individuals with hypochlorhydria (i.e., low stomach acid) or for people taking acid blockers for indigestion, acid reflux, or other intestinal conditions. Calcium citrate is also one of the best types of calcium supplements if you don’t always remember to take supplements with meals.

How to Take Calcium Supplements

  • When: Different types of calcium vary in whether they’re absorbed best with or without food. Calcium carbonate should be taken with meals. Calcium citrate can be taken on an empty stomach.
  • Caution: Calcium should not be taken with certain medications, including antibiotics, iron supplements, high blood pressure medications, and others. Calcium can bind to these medications and decrease their absorption. [4] Always speak to your pharmacist about medication interactions.
  • With: Calcium requires vitamin D to be absorbed properly. Many supplements are produced with both calcium and vitamin D included for this reason. Research has shown that taking vitamin K2 improves bone strength and bone mineral density in postmenopausal women, as well as reduces the rate of hip fracture. [5]
  • Dose: Approximately 500 mg of calcium can be taken at one time. Absorption from supplements is highest, with doses of 500 mg or less. [6] Calcium should be taken in divided doses rather than all at once. Separate doses into two or three times daily for optimal absorption. [7]

Calcium Supplement Guide

Form of Calcium Pros Cons A Good Choice For Product
Calcium carbonate • Readily available

• Inexpensive
• Needs to be taken with food

• Requires sufficient stomach acid for digestion
• Healthy, younger adults Calcium Carbonate, 5070
Calcium citrate • Much better absorbed than calcium carbonate

• Can be taken with or without food

• Doesn’t require stomach acid for absorption
• More costly than calcium carbonate

• Less readily available
• Adults over 50

• Adults with low stomach acid

• Individuals with osteopenia or osteoporosis

• Adults taking medications that block stomach acid

• Individuals regularly taking medications affecting bone health

• Individuals who often forget to take calcium with meals
Calcium Citrate 300 mg, 5016

Are There any Side Effects to Calcium Supplements?

Calcium is generally considered a safe mineral to supplement with and is well-tolerated when taken as recommended by the manufacturer. Some people might experience gastrointestinal side effects, including gas, bloating, constipation, or a combination of these symptoms.

Calcium carbonate may cause more of these side effects than calcium citrate, especially in older adults with lower levels of stomach acid. [8]

Sometimes, these symptoms can be alleviated by choosing a supplement containing a different form of calcium, like calcium citrate, taking smaller calcium doses more often during the day, or taking the supplement with meals.

If you take iron or zinc supplements, tetracycline antibiotics, or levothyroxine (used to treat hypothyroidism), take them several hours before or after taking calcium to avoid potentially negative interactions.

Concluding Thoughts on the Best Type of Calcium to Take

It should be obvious by now that there’s no simple answer to the question of which calcium supplement is best. The reality is that your unique physiology will guide your choice to best meet your needs. And what works well for a few weeks, months, or even years might need switching up as you get older, or if you’re more active, pregnant, nursing an infant, or develop a health condition like Crohn’s or irritable bowel syndrome.

If you think your current standard calcium supplement isn’t quite cutting it anymore, consider switching it out for one that’s easier on digestion and better absorbed.

Leigh Matthews, BA Hons, H.Dip. NT

Leigh Matthews, BA Hons, H.Dip. NT

A health and wellness writer specializing in plant-based nutrition and environmental health.

References :
  1. Osteoporosis Canada. 2022. Available from:
  2. Government of Canada. 2023. Available from:
  3. Beto JA. The role of calcium in human aging. Clin Nutr Res. 2015; 4(1):1-8.
  4. Watson J, Lee M, Garcia-Casal MN. Consequences of inadequate intakes of vitamin A, vitamin B12, vitamin D, calcium, iron, and folate in older persons. Curr Geri Rep. 2018; 7(2):103-13.
  5. Iwamoto, J., et al. (2000). Effect of combined administration of vitamin D3 and vitamin K2 on bone mineral density of the lumbar spine in postmenopausal women with osteoporosis. J Orthop Sci, 5(6), 546-551.
  6. Institute of Medicine. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D, and fluoride. Washington, DC: National Academies Press; 1997. 
  7. National Institutes of Health Office of Dietary Supplements. [Cited 2023 Mar]. Available from:
  8. Institute of Medicine. Dietary reference intakes for calcium and vitamin D. Washington, DC: The National Academies Press; 2011
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