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Calcium: Role in the body and dietary sources

Minerals, Diets | August 25, 2016 | Author: Naturopath


Calcium: Role in the body and dietary sources

Calcium is the most abundant mineral in the body, comprising up to 2 percent of the body weight of an average adult. Calcium is an essential mineral that is involved in maintaining important biological processes, although less than 1 percent of it is used in:

  • Nerve transmission
  • Heart contraction 
  • Muscular contraction and relaxation 
  • Blood clotting 
  • Hormonal secretion 
  • Heart rhythm regulation

The majority of the body's calcium, which is 1200 g in total, is stored and used in maintaining bone, health and function.

Calcium and Bone Healthshutterstock_296170832

Bone starts to form in the 13th week of life, and will undergo a lifelong process of breaking down and rebuilding. To maintain bone health, bone formation must exceed breakdown.

During childhood through young adulthood, bone forms faster than it is broken down, which is critical for developing the "bone bank". With adequate calcium intake, children and teenagers will achieve a bone mass of 99% by age 22, and maintain better bone health throughout life.

Calcium may also have other benefits like lowering blood pressure, decreasing risk for some cancers, facilitating weight loss, and preventing tooth loss in older adults.

Calcium deficiency

Inadequate dietary intake of calcium does not produce overt symptoms in the short term. In other words, you will not know that your calcium is running low because the body is smart, and controls calcium levels tightly. When the body senses that blood calcium levels are low, it draws calcium from the "bone bank" to maintain consistent levels. Of course, the bone bank won't run out of calcium that quickly, but in the long-term, calcium deficiency becomes a problem. In adults, calcium deficiency can cause osteomalacia, and osteoporosis. In children, chronic calcium deficiency results in a condition called rickets. Nowadays, at least in Western countries, rickets is most commonly caused by congenital anomalies in phosphate or vitamin D metabolism, and low vitamin D levels due to marked sunlight deprivation.

How much calcium do you need?

Age Group Calcium RDI (mg/day)

Babies 0–6 months approx. 210 (if breastfed) approx. 350 (if formula fed)

Babies 7–12 months 270

Children 1–3 years 500

Children 4–11 years 1000

Adolescents 12–18 years (including pregnant and breastfeeding young women) 1,300

Women 19–50 (including pregnant and breastfeeding women) 1,000

Women 51–70 1300

Men 19–70 1000

Adults >70 1300 Your calcium needs depend on your sex and age.

How much calcium do you need?Teenagers - because of their rapid bone growth, and older adults - because bone breakdowns more rapidly, have the highest calcium requirements.

In pregnancy it is not always necessary to take more calcium as calcium from food is absorbed more efficiently.

Australians are falling short on calcium

Data from the Australian Health Survey in 2011 found that over half of the Australian population aged 2 years and above failed to achieve their RDI for calcium. The survey also showed that three in four females (73%) from 2 years of age, were not meeting their calcium needs, compared with one in two males (51%). Not only are Australians falling short on calcium, they are consuming too much sodium, as well. Some experts attribute this trend to the shift from nutrient-dense foods towards highly-processed foods that are high in energy but have little nutritional value.

Practical Nutrition Tips

You can get calcium from either food or supplements, but it is still best to meet your nutritional (including calcium) needs by eating nutrient-dense foods that contain essential vitamins, minerals and dietary fibre.

Calcium from Dairy Products

Milk and dairy products have the highest concentrations of absorbable calcium. Three servings of milk and dairy per day will get you enough calcium.

Milk: 236ml of milk provides 300 mg of calcium. Whole milk with 4% fat is best for children ages 1 to 2. Low fat milk (1 to 2%) or skim milk, is best for adults and children over age 2. Removing the fat from milk does not affect its calcium content. Also, milk is a good source of magnesium, phosphorus and vitamin D.

Cheese: 42gs of (cheddar) cheese provides 303 mg of calcium. The rule of thumb is that hard cheeses (e.g parmesan, cheddar), have higher calcium concentrations than soft varieties (e.g Camembert, ricotta). Lactose-intolerant individuals are able to eat cheeses since the lactose has been broken down. 

Yoghurt: 237 ml of plain, low fat yoghurt provides 415 mg of calcium.

Non-dairy Sources

Leafy greens: Although dairy has the highest concentrations of calcium, you can also get a decent amount from vegetables.

Plants in the kale family, including broccoli, bok choy, cabbage, mustard and turnip greens, contain highly absorbable calcium as well. The only downside is that some plants contain oxalic acid (e.g spinach, sweet potatoes, beans) or phytic acid (e.g whole-grain products, wheat bran). These substances inhibit the absorption of calcium. Spinach, for example, contains 100 mg of calcium per cup, but only 5% of it may be absorbed.

Nuts and seeds: 30 g of almonds and hazelnuts will give you 75 mg and 56 mg, respectively.

Herbs: a cup of ground sage contains a whopping 1 652 mg of calcium.

Fish: 60 g of canned sardines in oil contains about 240 mg of calcium. Half a cup of canned salmon has 402 mg. Try eating the bones in canned fish!

Vitamin D from Food

The best known function of vitamin D is to increase absorption of calcium and phosphorus in the intestines and kidneys. Without vitamin D, only about 10% to 15% of calcium and 60% of phosphorus from the diet can be absorbed, compared to 30% to 40% calcium and 80% phosphorus absorption when the vitamin levels are normal.

Foods high in vitamin D include:

  • Fatty fish (e.g mackerel, tuna, salmon, sardines)
  • Cod liver oil
  • Beef liver
  • Egg yolk
  • Cheese
  • Vitamin D fortified milk 
  • Vitamin D fortified breakfast cereals


Your lifestyle choices affect your overall health, including how much calcium your body absorbs or loses.

Get Enough Sunshine

You can get vitamin D from food sources, but not everybody can meet their daily requirements through food alone. Sunshine is the richest source of vitamin D. When UVB rays from the sun hit the skin, it triggers biochemical reactions necessary for the creation of the biologically-active hormone, calcitriol or vitamin D. Fair skinned individuals are recommended to get at least 5 minutes direct sun exposure between 10 am and 2 pm during summers, and at least 7 minutes during winter. Darker skinned individuals should get at least 15 minutes of sunshine during the summer, and at least 20 minutes during winters.

Reduce Sodium, Caffeine and Alcohol Intake

High sodium intakes increase calcium loss in urine. Caffeine, at 4 cups or more per day, can increase calcium loss and inhibit calcium absorption. Alcohol can also affect calcium by inhibiting the vitamin D production.

Calcium Supplements

Calcium SupplementsAlthough it is best to get calcium from food, there are some people who need supplements, including:

  • Postmenopausal women
  • Older adults
  • Individuals with major illnesses 
  • Individuals on long-term corticosteroid therapy
  • Individuals with malabsorptive syndromes (e.g coeliac disease, inflammatory bowel disease)

There are several different kinds of calcium compounds used in supplements. The supplements vary in elemental calcium content. The most commonly used calcium supplements are calcium carbonate and calcium citrate.

Calcium Carbonate

Calcium carbonate provides 200 mg elemental calcium per 500 mg pill. It is effective and is the cheapest form of calcium. Because calcium carbonate depends on stomach acid for absorption, it is most efficiently absorbed when taken with a meal, especially a low-iron meal.

For this reason, calcium carbonate may not be best for people with low stomach acid, inflammatory bowel disease, and those taking medication for gastro-oesophageal reflux disease (e.g ranitidine), which inhibits stomach acid production.

Calcium Citrate

Calcium citrate is the best absorbed type of supplement, which does not require extra stomach acid for absorption. You can take it at any time, with or without food. Calcium citrate is best for people with low stomach acid and inflammatory bowel disease. Calcium citrate provides less elemental calcium per pill than the carbonate form. This means that you may need to take more pills per day to meet your calcium needs, considering that 500 mg of calcium citrate provides only 105 mg of elemental calcium.

Plant-based Calcium

Algae calcium supplements come from the red algae called Lithothamnion calcerum. During its lifetime, the algae gathers minerals from the ocean, and when it dies, it leaves behind its skeleton, which is rich in calcium, and up to 70 other minerals, including magnesium and phosphorus. There have been studies showing that algae supplements may be able to increase bone mineral density, but there have been no well-designed clinical trials comparing them with a placebo, or conventional calcium supplements in terms of efficacy and safety. Also, algae supplements may contain lead.

The Takeaway

In terms of bioavailability and absorbability, calcium citrate is better than calcium carbonate. According to a study published in the Journal of Clinical Pharmacology, calcium citrate was 2.5 times more bioavailable than calcium carbonate, even when given with a meal. Also, calcium citrate suppressed parathyroid hormone secretion, which is responsible for bone loss, by more than 50% compared with calcium carbonate. Calcium supplements are best absorbed when taken at small doses of 500 mg or less at one time. So, it would be best to divide large doses (e.g morning and evening). To maximize absorption, make sure to avoid foods high in oxalic and phytic acid mentioned above.  Australia’s best online discount chemist

Australian Health Survey: Nutrition First Results - Food and Nutrients, 2011-12

NIH Consensus conference. Optimal calcium intake. NIH Consensus Development Panel on Optimal Calcium Intake. JAMA 1994; 272:1942.

Bedford JL, Barr SI. Higher urinary sodium, a proxy for intake, is associated with increased calcium excretion and lower hip bone density in healthy young women with lower calcium intakes. Nutrients. 2011;3(11):951-961

Calcium Citrate Shown to Have Superior Bioavailability and Protects Against Bone Loss. J Clin Pharmacol. 2000;40:1237-12 5. Heaney RP. Bone mass, nutrition, and other lifestyle factors. Nutr Rev. 1996;54(4 Pt 2):S3-S10.

Heaney RP. Calcium, dairy products and osteoporosis. J Am Coll Nutr. 2000;19(2 Suppl):83S-99S.

Weaver CM. Calcium. In: Erdman JJ, Macdonald I, Zeisel S, eds. Present Knowledge in Nutrition. 10th ed: John Wiley & Sons, Inc.; 2012.

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