Calcium in Nutrition

A display of various foods which all contain calcium as a mineral.
Foods containing calcium. Copyright: photka / 123RF Stock Photo

The body contains more calcium than any other mineral – in fact we store 99% of it in our bones and teeth. The rest is found in our blood, muscle and extracellular fluid (Laine et al., 2008). Given the amount in our bodies, it is often the situation that we are not eating enough foods containing  this mineral. It is certainly the case in the USA, that on average Americans have a generally low calcium intake. We need 700 mg of calcium per day for the great variety of functions it performs.

To be more specific about this mineral, it is required for:-

– Building strong bones and teeth

– Regulating muscle contraction and heart rhythm

– Proper blood clotting

– Proper secretion of hormones and enzyme

– Nervous system control and conduction (Glade, 1997)

– weight maintenance and management

Without calcium we would suffer from some major health problems related to weakening of bones. One of the worst conditions of too little calcium early on in life is rickets as children. Indeed, some children never reach their full potential in adult height when this deficiency occurs and osteoporosis in later life.

Calcium deficiency can produce some severe chronic conditions. Whilst many Americans do not get enough calcium in their diet, children and adolescent girls in particular are at risk because they do not drink as much milk as they could. Adults over the age of 50 are also at risk.

It is also the case that phytates in cereals and oxalates in spinach for example reduce the bioavailability of calcium.

Calcium my help in lowering blood pressure (McCarron and Reusser, 2001) and protecting against colon and breast cancer.

If we want our bodies to properly absorb and use calcium, we also need other essential nutrients such as vitamin D, vitamin K and another mineral, magnesium. There is a general consensus amongst nutritionists that as we age, or if we are pregnant or nursing then we require extra calcium.

We now look at some of the natural sources and some of the conditions that are helped by calcium supplementation.  

What Is Calcium ?

Calcium is a silvery-white metal in  Group 2 of the Periodic table. Its atomic weight is 40.08 and has an atomic number of 20. Its symbol is Ca. It is found in chalk, limestone and gypsum. It is a common enough mineral which is found in virtually all vertebrates such as animals because it is the a key component of bone and shells.

Sources Of Calcium:

  • Eating a healthy balanced diet is essential to meet all our dietary requirements including calcium.
  • Milk, cheese, dairy foods
  • Leafy green vegetables like cabbage, broccoli, okra but not spinach.
  • Soya beans and soya drinks with added calcium
  • Tofu
  • Nuts
  • Bread and baked goods with fortified flours
  • Fish where the bones are also eaten like pilchards.
  • It is fair to say that natural food sources and  complex supplements are better sources because of the range of other minerals and vitamins they contain. Look for calcium-fortified foods. Generally, calcium supplements which only contains calcium are used in extreme circumstances.

What Is The Daily Requirement For Calcium ?

The recommended daily allowance (RDA) for calcium is currently 1 gram per day for both adult men and women under the age of 50. As we get older, the RDA rises to between 1.2 grams and 2 grams per day for adults between the ages of 50 and 70 and as we get older. This calcium is needed to replace that lost from bones that are aging. The Mayo Clinic has an excellent review on how to achieve the right balance as we age.

The Top 10 Foods Containing Calcium

Dairy foods are one of the best sources of calcium but they are by no means the highest. Milk is especially good but there are a number of plant and animal based foods which can also supply calcium. Look for nuts, beans and vegetables if you are vegetarian or vegan (Miller et al., 2001).

   Sardines   (tinned and with bones included)     1 cup   569 mg    57% DV 
Yogurt or kefir   1 cup 488mg 49% DV
Raw milk (whey protein, products made with milk) 1 cup 300mg 30% DV
Cheese   1 ounce 202mg 20% DV
Kale raw 1 cup 90.5mg 9% DV
 Okra raw 1 cup 81mg 8% DV
Bok Choy  raw 1 cup 74mg 7% DV
Almonds  raw 1 ounce 73.9mg 7% DV
Broccoli  raw 1 cup 42.8mg 4%
Watercress  raw 1 cup 41mg     4%

Supporting Bone Health

It is estimated that about 10 million US citizens are affected by osteoporosis. This condition is one of the leading causes of fracture and broken bones especially in the elderly and affects both sexes although it is more prevalent in women than men. Generally, any foods high in calcium support bone and skeletal growth.

Possible Prevention Of Cancer

Consuming calcium rich foods is associated with a decrease in certain types of cancer, especially the colon and rectal cancers. A major study, American Cancer Society’s Cancer Prevention Study II Nutrition Cohort study has shown in both men and women that those who had the highest intakes of calcium in their diet and/or through supplementation had the lowest risk of developing colorectal cancer when compared with those who had the lowest calcium intakes.

Calcium supplementation is not recommended for preventing colon cancer or indeed any other cancer for that matter, but foods high in calcium appear to have certain benefits. There are claimed to be links between calcium supplements and heart attack. There is also potentially a higher risk with prostate cancer and supplementation (National Cancer Institute web-site).

Could It Reduce The Formation Of Kidney Stones ?

Kidney stones are usually crystals of calcium with other minerals which form in the kidney and pass through the human urinary tract. They cause extreme irritation and inflammation if they become lodged in the tract.

The most common form of kidney stones are salts formed with oxalate anions. We have often thought that a high calcium intake promotes the development of these types of stones.  The oxalate concentration is key to this phenomenon as it is probably too high a level which precipitates out when it crystallises with calcium ions. On that basis, a reasonably high dietary calcium intake actually decreases the risk of kidney stones because calcium oxalate forms routinely and is flushed away into our urine before the oxalate levels reach their crystallisation point.  There may be a stronger negative association with drinking soft water and stone formation which has little calcium in it.  Other factors such as a high oxalate consumption from leafy vegetables like rhubarb, kale and spinach, as well as a low fluid consumption might also be implicated in stone formation but it is not entirely certain. It has much to do with how our body regulates calcium levels in blood and tissue. 

  • The best thing to do is drink plenty of water regularly. It simply helps to prevent stone formation and slowly dissolve those that are in the process of forming !

Magnesium is the second most important mineral in terms of quantity in the body.

See the NHS web-site which provides a fine overview on this mineral !

References

Glade, M.J. (1997). Calcium and Related Nutrients – A workshop sponsored by the panel on calcium and related nutrients of the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine, Washington, DC, – July 9–10, 1996. Nutrition, 13, pp. 721– 724.

Laine, J., Labady, M., Albornoz, A., Yunes, S. (2008). Porosities and pore sizes in coralline calcium carbonate. Materials Characterization, 59, pp. 1522–1525.

McCarron, D.A. & Reusser, M.E. (2001). Are low intakes of calcium and potassium important causes of cardiovascular disease? American J. Hypertension, 14, pp. 206s–212s.

Miller, G.D., Jarvis, J.K. McBean, L.D. (2001) The Importance of meeting calcium needs with foods. J. Am. Coll. Nutr. 20 (2 suppl.) pp, 168s-185s https://www.ncbi.nlm.nih.gov/pubmed/11349940

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