What is Calcium?

Calcium is one of the most abundant minerals in the human body, making up approximately 1-2% of an adult’s body weight¹. It plays an important role in maintaining bone strength and supporting numerous bodily functions, from muscle contraction to nerve conduction. Despite its importance, many people (particularly breastfeeding women) don’t get enough calcium from their diet alone. According to the Australian Bureau of Statistics survey, over half of all Australians aged 2 years and over consume inadequate levels of calcium from food sources, with 73% of females and 51% of males consuming less than the recommended amounts. This comprehensive guide explores what calcium is, its vital functions in the body, how to maintain optimal levels, and when supplements might be necessary.¹⁷

The Importance of Calcium for the Body

Calcium is a mineral essential for human health and physiological function. It is the fifth most abundant element in the earth’s crust and is classified as an alkaline earth metal on the periodic table⁴. In the body, calcium exists primarily as calcium ions, which carry an electric charge when dissolved in bodily fluids like blood. Almost all calcium in the body (about 99%) is stored in bones and teeth, giving them structure and hardness^2,3.
 
Beyond its structural role, calcium is fundamental to countless biochemical processes that keep us healthy and functioning optimally. Without adequate calcium, our bodies cannot perform essential functions efficiently, potentially leading to both short-term symptoms and long-term health conditions.

What Does Calcium Do for the Body?

Calcium’s functions extend far beyond bone health, though that remains its most well-known role. This mineral contributes to:
 
Bone and Tooth Formation: Calcium provides the structural framework for bones and teeth, making them strong. Throughout life, bones undergo continuous remodeling-a process where old bone is broken down and new bone is formed-requiring a steady supply of calcium^2,3.
 
Muscle Contraction: Calcium is essential for muscle function, including the heart. When nerve impulses stimulate muscles, calcium ions facilitate the interaction between muscle proteins that cause contraction. Without sufficient calcium, muscle weakness and cramping can occur^2,3.
 
Nerve Transmission: Calcium helps nerves carry messages between the brain and every part of the body, it acts as a messenger.
 
Enzyme Activation: Many enzymes require calcium to function properly.

Calcium Insufficiency Symptoms

Calcium insufficiency may initially be asymptomatic, particularly when mild. However, as insufficiency progresses, various symptoms may develop:
 
Muscle Problems: One of the earliest and most common signs includes muscle aches, cramps, and spasms.
 
Bone Health Issues: Long-term calcium insufficiency leads to decreased bone density, which may progress to osteoporosis-a condition characterized by brittle bones. This occurs because when blood calcium levels drop, the body extracts calcium from bones to maintain essential functions^3,5,6.
 
Dental Problems: Insufficient calcium can affect tooth health.
 
PMS: Calcium insufficiency may be linked to premenstrual syndrome symptoms in women⁶.
 

Recommended Daily Calcium Intake

Calcium needs vary throughout life, with higher requirements during periods of growth (childhood and adolescence) and in later life, particularly for women after menopause when bone loss accelerates.

How Much Calcium Per Day is Needed?

The recommended daily intake of calcium varies by age and life stage:

• Infants 0-6 months: 200 mg²
• Infants 7-12 months: 260 mg²
• Children 1-3 years: 700 mg²
• Children 4-8 years: 1,000 mg²
• Children and teens 9-18 years: 1,300 mg²
• Adults 19-50 years: 1,000 mg²
• Men 51-70 years: 1,000 mg²
• Women 51-70 years: 1,200 mg²
• Adults 71 years and older: 1,200 mg²
• Pregnant and breastfeeding teens: 1,300 mg²
• Pregnant and breastfeeding women: 1,000 mg²

These recommendations aim to support bone health and prevent insufficiency-related conditions like osteoporosis. Meeting these targets through diet is ideal, but supplements may be necessary for those who struggle to consume enough calcium-rich foods.

Can I Take Calcium on an Empty Stomach?

While calcium can be taken on an empty stomach, absorption may be improved when taken with food. Different forms of calcium have different absorption characteristics:
 
Calcium carbonate, the most common and least expensive form, requires stomach acid for proper absorption and is best taken with meals.
 
Calcium citrate can be taken with or without food as it doesn’t require stomach acid for absorption, making it a better choice for older adults or those taking acid-reducing medications.
 
For the best possible absorption, calcium supplements should be taken in doses of no more than 500-600 mg at once, as the body has limited capacity to absorb larger amounts in a single sitting. Spreading intake throughout the day maximizes absorption efficiency.⁸

Dietary Sources of Calcium: What Foods Have Calcium?

While supplements can help bridge nutritional gaps, obtaining calcium from food sources is generally preferred as foods provide additional nutrients that support calcium absorption and utilization.

Dairy (Milk, Cheese, Yogurt)

Dairy products are among the richest and most bioavailable sources of calcium. One cup (250ml) of milk provides approximately 300mg of calcium, while a 200g tub of yogurt offers similar amounts. Hard cheeses like cheddar and parmesan contain even higher concentrations per serving⁵.

Leafy Greens

Dark leafy greens, particularly those low in oxalates (which can inhibit calcium absorption), provide modest but important calcium contributions. Kale, bok choy, and turnip greens are better calcium sources than spinach, which contains higher oxalate levels that reduce calcium bioavailability⁵.

Fortified Products

Many plant-based milks (soy, almond, oat), juices, and breakfast cereals are fortified with calcium, often providing amounts comparable to dairy milk. These products are particularly important for those following vegetarian, vegan, or dairy-free diets⁵.

Fish with Bones (Sardines)

Small fish consumed with their soft bones, such as sardines and canned salmon, provide excellent calcium. A 100g serving of sardines can contain around 380mg of calcium⁵.

How to Get Calcium Without Dairy

For those who avoid dairy due to lactose intolerance, milk allergy, or dietary preferences, numerous non-dairy calcium sources exist:

• Calcium-fortified plant milks (soy, almond, rice)
• Tofu made with calcium sulfate
• Tempeh and natto (fermented soy products)
• Sesame seeds and tahini
• Almonds and almond butter
• Dried figs
• White beans, chickpeas and other legumes
• Calcium-set tofu
• Fortified orange juice
• Blackstrap molasses

These options can help maintain adequate calcium intake without consuming dairy products⁵.

Do Eggs Have Calcium?

Eggs contain relatively modest amounts of calcium-approximately 27mg per 50g of egg. While eggs provide high-quality protein and various micronutrients, they are not considered significant calcium sources and should be complemented with other calcium-rich foods⁹.

Does Lactose-Free Milk Have Calcium?

Yes, lactose-free milk contains the same amount of calcium as regular milk. The lactose-free processing involves adding the enzyme lactase, which breaks down lactose (milk sugar) but doesn’t affect calcium content. This makes lactose-free milk an excellent calcium source for those with lactose intolerance.

Does Soy Milk Contain Calcium?

Unfortified soy milk contains relatively small amounts of naturally occurring calcium, around 26mg. However, most commercial soy milk is fortified with calcium to levels comparable to cow’s milk (approximately 240mg per cup). When selecting soy milk for calcium content, check the nutrition label to ensure it’s fortified¹⁰.

Do Almonds Have Calcium?

Yes, almonds are one of the nuts highest in calcium. A 30g serving (approximately 23 almonds) provides about 75mg of calcium. While not as calcium-dense as dairy, almonds offer a plant-based option that contributes to overall calcium intake while providing healthy fats, vitamin E, and magnesium¹⁰.

Does Broccoli Have Calcium?

Broccoli contains moderate amounts of calcium-about 112mg per 120g serving.¹⁰

How Much Calcium is in an Orange?

A medium-sized orange contains approximately 60mg of calcium. While oranges aren’t major calcium contributors, they provide vitamin C.¹⁰

Potential Risks and Interactions of Calcium Supplements

While calcium supplements can help meet nutritional requirements, they should be used cautiously as excessive supplementation may carry risks.

Do Calcium Supplements Cause Constipation?

Constipation is one of the most common side effects of calcium supplements, particularly with calcium carbonate. This effect varies between individuals and often depends on the form and dosage of calcium. Taking supplements with plenty of water, increasing dietary fiber, and physical activity can help mitigate this effect. Alternatively, calcium citrate typically causes fewer digestive issues than calcium carbonate.

Can Calcium Tablets Make You Feel Sick?

Some people experience digestive discomfort such as gas, bloating, or nausea when taking calcium supplements. Taking calcium with food, choosing a different calcium formulation, or reducing the dose taken at one time may help reduce these symptoms. If discomfort persists, consulting a healthcare provider is recommended.¹²

Does Calcium and Magnesium Compete for Absorption?

Calcium and magnesium use similar absorption pathways in the intestine, potentially competing at very high doses. However, under normal supplementation conditions, this competition is minimal.

FAQ

Is Calcium a Metal?

Yes, calcium is classified as an alkaline earth metal on the periodic table. It’s a silvery-gray metal in its pure elemental form with the atomic number 20. In nature and in the body, calcium is found in compound forms rather than as a pure metal⁴.

Does Nonfat Milk Have Calcium?

Yes, nonfat (skim) milk contains approximately the same amount of calcium as whole milk-about 300mg per cup. The fat removal process doesn’t affect calcium content, making nonfat milk an excellent calcium source for those limiting fat intake.¹⁴

Can I Eat Vitamin D and Calcium Together?

Not only can vitamin D and calcium be taken together, but this combination is often recommended. Vitamin D plays a crucial role in calcium absorption from the digestive tract. Without adequate vitamin D, the body can only absorb 10-15% of dietary calcium, compared to 30-40% with sufficient vitamin D levels³.

Does Banana Contain Calcium?

Bananas contain relatively small amounts of calcium-approximately 5-6mg per medium banana. While bananas offer other nutritional benefits like potassium, vitamin B6, and fiber, they should not be relied upon as a significant calcium source in the diet.¹⁶

References

[1]Institute of Medicine (US) Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. (1997) Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academies Press (US). Available at: https://www.ncbi.nlm.nih.gov/books/NBK109827/ (Accessed: 9 May 2025).
 
[2]National Institutes of Health Office of Dietary Supplements. (n.d.) ‘Calcium – Consumer’, NIH Office of Dietary Supplements. Available at: https://ods.od.nih.gov/factsheets/Calcium-Consumer/ (Accessed: 9 May 2025).
 
[3]Lewis III, J.L. (2023) ‘Overview of Calcium’s Role in the Body’, MSD Manual Consumer Version. Available at: https://www.msdmanuals.com/home/hormonal-and-metabolic-disorders/electrolyte-balance/overview-of-calcium-s-role-in-the-body (Accessed: 9 May 2025).
 
[4]LibreTexts. (2023) ‘Chemistry of Calcium (Z=20)’, Chemistry LibreTexts. Available at: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/1_s-Block_Elements/Group__2_Elements:_The_Alkaline_Earth_Metals/Z020_Chemistry_of_Calcium_(Z20) (Accessed: 9 May 2025).
 
[5]Better Health Channel. (n.d.) ‘Calcium’, Better Health Channel. Available at: https://www.betterhealth.vic.gov.au/health/healthyliving/calcium (Accessed: 9 May 2025).
 
[6]Medical News Today. (2018) ‘What to know about calcium deficiency’, Medical News Today. Available at: https://www.medicalnewstoday.com/articles/321865 (Accessed: 9 May 2025).
 
[7]MSD Manual Consumer Version. (n.d.) ‘Hypercalcemia (High Level of Calcium in the Blood)’, MSD Manual Consumer Version. Available at: https://www.msdmanuals.com/home/hormonal-and-metabolic-disorders/electrolyte-balance/hypercalcemia-high-level-of-calcium-in-the-blood (Accessed: 9 May 2025).
 
[8]Harvard Health Publishing. (n.d.) ‘Choosing a calcium supplement’, Harvard Health. Available at: https://www.health.harvard.edu/nutrition/choosing-a-calcium-supplement (Accessed: 9 May 2025).
 
[9]International Osteoporosis Foundation. (n.d.) ‘Calcium Content of Common Foods’, International Osteoporosis Foundation. Available at: https://www.osteoporosis.foundation/patients/prevention/calcium-content-of-common-foods (Accessed: 9 May 2025).
 
[10]Healthy Bones Australia. (2022) ‘Calcium-Rich Food List’, Healthy Bones Australia. Available at: https://healthybonesaustralia.org.au/wp-content/uploads/2022/10/calcium-rich-food-list_en_1_healthybonesaustralia-iof-version-draft-1.pdf (Accessed: 9 May 2025).
 
[12]Barat, J. (2024) GoodRx Health. (n.d.) ‘Calcium Citrate: Side Effects, Dosage, Uses, and More’, GoodRx Health. Available at: https://www.goodrx.com/well-being/supplements-herbs/calcium-citrate-side-effects (Accessed: 9 May 2025).
 
[13]Behar, J.. (1975) ‘Effect of calcium on magnesium absorption,PubMed. Available at: https://pubmed.ncbi.nlm.nih.gov/1211491/ (Accessed: 9 May 2025).
 
[14]Eat This Much. (n.d.) ‘Nonfat Milk Nutrition Facts’, Eat This Much. Available at: https://www.eatthismuch.com/calories/nonfat-milk-74 (Accessed: 9 May 2025).
 
[15]Gaitan, D. (2011) ‘Calcium does not inhibit the absorption of 5 milligrams of nonheme or heme iron at doses less than 800 milligrams in nonpregnant women’, Elsevier. Available at: https://pubmed.ncbi.nlm.nih.gov/21795430/ (Accessed: 9 May 2025).
 
[16]Australian Food Composition Database. (n.d.) ‘Food Details: F000262’, Food Standards Australia New Zealand. Available at: https://afcd.foodstandards.gov.au/fooddetails.aspx?PFKID=F000262 (Accessed: 9 May 2025).
 
[17]ABS, Australian Health Survey: Usual Nutrient Intakes. 2011 12, cat. no. 4364.0.55.008.