Calcium is one of the most abundant minerals in the body, with 98% being found in the bones and 1% in the tissues (Ballentine, 2007).
Why Is Calcium Important?
Calcium is needed in the diet (in conjunction with over vitamins and minerals) for normal bone growth and maintaining healthy bones and teeth (Mann & Truswell, 2002). Bones undergo constant renovation through cells termed osteoclasts and osteoblasts. Old parts of the skeleton are chiselled away and then reabsorbed by osteoclasts, while new teams of osteoblasts rebuild strong new bone by depositing calcium (Mann & Truswell, 2002). If there is not enough calcium in the diet then the bones can become brittle and thin, and diseases such as osteoporosis can occur.
Another, key role of calcium is in the concentrations of calcium between the intracellular fluids and extracellular fluids; which are tightly controlled by the calicotrophic hormones (Mann & Truswell, 2002). The interaction between these calcium ions with proteins alters molecular activity, such as muscle contractions, nerve conductivity, ion transport, enzyme activation, blood clotting and secretion of hormones and neurotransmitters (Wright and Lenard, 2001). Therefore, even small alterations in someone’s calcium levels can have major repercussions.
Calcium has some other minor functions in the body as well, but the two above are it’s key roles.
What Influences Calcium Absorption?
Diet can also influence calcium levels in terms of absorption and extraction. Calcium absorption is a two fold process – first the stomach has to extract the calcium from the source and then get it into a solution (Wright and Lenard, 2001). Therefore, people with low stomach acid will find it difficult to extract and absorb calcium. Low stomach acid can occur for a multitude of reasons, notably from medications (e.g. antacids) or simply old age. Another factor affecting absorption, is how well a person tolerates lactose. The enzyme lactase enables the breakdown of lactose and thus absorption of calcium from dairy sources (Ballentine, 2007).
There are some factors affecting the bioavailability of calcium from the intestines, notably other vitamins and minerals in the diet. Vitamin D increases absorption of calcium from the intestines, through its dependent relationship with parathyroid hormone. The parathyroid hormone is released when blood concentrations of calcium decrease. This triggers a mixture of three responses – kidneys to release calcium by reabsorption, the bones to decalcification and the gut to increase absorption in food. This ensures that plasma calcium levels are constant. This means that if blood calcium levels are low, then calcium from the bones can be used; thus decreasing the bone calcium levels.
Once calcium is absorbed into the bloodstream vitamin D has no power over it (Rhéaume-Bleue, 2012). It is Vitamin K2 that allows calcium deposits in bones to increase. Vitamin K2 works by activating a number of special proteins (osteocalcin and matrix gla protein that move calcium around the body). It is the osteocalcin that attracts calcium to the bones and teeth and the matrix gla protein that binds to calcium and sweeps it out of soft tissues like arteries and veins, where the minerals are unwanted and harmful (Rhéaume-Bleue, 2012). Consequently, if one’s Vitamin K2 levels are low then calcium may not be deposited appropriately in the bones.
Calcium & Peak Bone Mass
Once a woman reaches her 20’s she will reach her peak bone mass – the heaviest bone mass that an individual achieves (Mann & Truswell, 2002).
Calcium levels are important to keep constant after peak bone mass is reached to ensure the body’s bone density doesn’t decline too much. A decline in bone density can lead to diseases such as osteoporosis or increased risk of bone fractures (i.e. the lower the bone density, the weaker the bone and thus the higher likelihood of it breaking). Osteoporosis is the gradual decline in bone density, leading to increased fragility of the bone and thus higher susceptibility of fractures.
In addition, as women approach menopause it is likely that the bone mass will decline further, due to the drop is the hormone oestrogen. It’s important to note that in one’s life their bone density will decline after they reach their PMB, but if it declines too fast then diseases can occur. For example, post menopause women are expected to lose on average 1-2% of bone over a 5-10 year period (Mann & Truswell, 2002). Therefore, it’s important to ensure the diet has adequate calcium.
How Is Calcium Lost?
Each day the body loses small amounts of calcium through faces (80-120mg), sweat (<20mg) and urine (40-200mg) (Mann & Truswell, 2002). Some other dietary choices influence losses, such as caffeine and salt intake.
Risks Associated With Too Much Calcium
Rhéaume-Bleue (2012) coined a term called the Calcium Paradox, for the mysterious calcium deficiency in the skeleton and calcium excess in the arteries (calcification), which many doctors were seeing. She believes this ‘paradox’ underlies the two major chronic illnesses of our time – osteoporosis and heart disease. When the vitamins are deficient (i.e. vitamin D and vitamin K2) we say that the dependent proteins are ‘under carboxylated’ and thus calcium can’t be deposited in the bones and instead is left in the arteries.
The US Dietary recommendations recommend 1000mg / day for a woman aged 31 – 50 years old and the upper limit of daily intake being 2,500mg / day (Mann & Truswell, 2002). Whereas, the NHS only recommends 700mg of calcium a day (NHS, 2020). It is recognised that daily calcium intake varies from person to person, due to genetics, nutritional status, gender, ethnicity and current daily intake. As a reference a 250ml glass of milk has 300mg calcium and one portion of broccoli has 200mg (Ballentine, 2007).
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Ballentine, R,. 2007. Diet & Nutrition – A Holistic Approach. 2nd ed. Himalayan Institute.
Mann, J. and Truswell, S. ed., 2002. Essentials Of Human Nutrition. 5th ed. Oxford: Oxford University Press.
NHS, 2020. Vitamins And Minerals – Calcium. [online] nhs.uk. Available at: <https://www.nhs.uk/conditions/vitamins-and-minerals/calcium/> [Accessed 18 December 2020].
Rhéaume-Bleue, K., 2012. Vitamin K2 And The Calcium Paradox. 2nd ed. Toronto: Collins.
Wright, J. and Lenard, L., 2001. Why Stomach Acid Is Good For You. 1st ed. New York: M. Evans.