Calcium is generally associated with bone health and healthy teeth. Contrary to their appearance, bone is living tissue that is constantly being broken down and build up again, depending on the calcium contents and needs of the body. The bone production of healthy individuals, who get enough dietary calcium and exercise, exceeds bone destruction – but only up to the age of 30. After age 30, bone destruction typically exceeds bone production. As people age, the body becomes less efficient at absorbing calcium – and other nutrients. Getting higher amounts of calcium from food or supplements will not necessarily resolve this problem.
Older people – especially women who have reached menopause – are at risk to develop weak and fragile bones, a condition called osteoporosis. Many people take calcium supplements, hoping to strengthen their bones and making them less porous. However, some studies associate a very high intake of calcium supplements with several health risks.
What role does calcium play in the body?
The body does not produce calcium, an important mineral, but gets it through dietary sources and by drawing from calcium in the bones. Calcium is the most abundant mineral in the body and, in combination with phosphorus, forms calcium phosphate, which is the dense, hard, material of the bones and teeth. The primary role of calcium is to build and maintain strong bone and it is no wonder that over 99% of the calcium in the body is stored in the bones and teeth.
The parathyroid hormone (secreted by 4 parathyroid glands in the neck, situated behind the thyroid gland) causes the transfer of calcium from bone into the blood stream and together with calcitonin (a hormone produced in the thyroid gland) maintains calcium balance in the blood by preventing either calcium deficit or excess. Low calcium levels in the blood stimulates the release of parathyroid hormone, which increases calcium levels in the blood when they are low, while calcitonin acts to reduce calcium levels in the blood when they become too high.
Parathyroid hormone stimulates the release of calcium from bones into the blood stream, signals the kidneys to release less calcium in the urine, and increases calcium absorption from food by activating vitamin D metabolism to improve the absorption of calcium in the intestines. Calcitonin opposes the action of parathyroid hormone and lowers the calcium levels in the blood by ending the release of calcium from bones and signaling the kidneys to release more calcium in the urine.
Calcium plays an important role in regulating the way all muscles in the body contract and relax.
- Skeletal muscles are attached to bone and contraction takes place voluntary, as you decide when to contract your muscles.
- Cardiac muscles are the main components of the heart, with involuntary contractions that occurs spontaneously.
- Smooth muscles are the major components of the bladder, the uterus, blood vessels, airways, and the organs of the gastro-intestinal tract. Contractions are involuntary and occurs slower than the cardiac muscles, from many different types of stimuli. These muscles do not exhibit complete relaxation after contraction, as for example the complete relaxation of muscles in the blood vessels would result in blood pressure dropping to dangerous levels.
Calcium has many other functions in the body, such as affecting the permeability of cell membranes, being used to send nerve signals, and plays a role in the release hormones such as insulin.
Calcium levels and supplements:
Studies have shown that both calcium and vitamin D are essential for building bone and vitamin D’s most well-known function is to maintain normal blood levels of calcium. It acts as facilitator for the absorption of calcium from the gut, as vitamin D switches on the gene that induces synthesis of a calcium binding protein that is responsible for the absorption of calcium from food in the gut. Scientists recommend taking vitamin D supplements with calcium supplements to improve the absorption of calcium. Harvard recommends lower doses of calcium and higher doses of vitamin D.
Calcium supplements can be used to fill the gap between the amount of calcium you get from your diet and the daily recommended intake of calcium that the body needs. But how much the body really needs is not always clear. The traditional guidelines from the 1970’s from the American Institute of Medicine recommends a daily intake of 1 000 mg per day for adults and 1 200 mg per day for women over the age of 50 and men over 70, with an upper limit of 2 500 mg per day.
However, Harvard Medical School recently (2019) warned that these recommendations may be too high and could do more harm than good. Harvard says you’ll probably do just as well with half these amounts and agrees with the guidelines from the World Health Organization of 500 mg per day. According to Harvard the guidelines from the 1970’s is based on the results of a couple of brief calcium balance studies that lasted a few weeks, while calcium balance is actually determined over the course of years. In addition, the body cannot absorb large doses of calcium at once and taking a maximum of 500 mg in supplement form is recommended.
A randomized study in New Zealand in 2013 has associated calcium supplements with the potential to contribute to heart attacks and heart disease. This study raised concerns, but later studies were inconclusive. However, excess calcium in the form of high doses of calcium supplements may play a role in vascular disease, as the excess that don’t make it to the skeleton or get completely excreted in the urine, may accumulate in blood vessels in the form of plaque, which can impede blood flow and raise the risk of heart attack. Excess amounts of calcium have also been linked to the risk of developing kidney stones.
The scientific way to determine calcium levels and whether you need supplements, is to measure the amount of calcium in the blood. The total calcium blood test measures what it says, the total amount of calcium in the blood. A secondary test, the ionized calcium blood test, measures the amount of “free” calcium (calcium not bound to any proteins) present in the blood. Calcium can further be measured in the urine.
The normal reference range for the total calcium blood test in adults is between 8,6 and 10,2 milligrams per deciliter (mg/dL). Higher than normal levels relate to a condition called hypercalcemia, while lower than normal levels relate to a condition called hypocalcemia. These measurements will assist your medical practitioner to identify and treat any condition that may result in abnormal levels of calcium in the blood stream.
Sources of calcium:
As mentioned earlier, the body needs to obtain calcium from dietary sources and supplements, as it is not made in the body. Taking a supplement may not be the most effective way to boost calcium intake, as a nutrient in pill form is not processed in the same way in the body as a food source. Calcium from the diet is better absorbed, as you get it in small amounts spread throughout the day along with other food sources.
Dietary sources of calcium include a variety of foods, such as:
- Dairy products, such as milk, cheese, yogurt.
- Leafy green vegetables, such as spinach, broccoli, kale.
- Canned fish with edible, soft bones, such as sardines or salmon.
- Beans and lentils.
- Calcium fortified food and drinks.
- Tofu.
- Almonds.
As calcium is a large mineral, it is not easily broken down in the gut. Not all of the total amount of calcium in food is absorbed, as it depends on the calcium bioavailability of the specific food item. For example, dairy foods have a bioavailability of about 30% absorption and while a milk container may indicate 300 mg of calcium per cup, only 100 mg (30%) will be absorbed and used by the body. Plant sources of calcium may have less total calcium but have a higher bioavailability than dairy products. An example in this regard is bok choy which contains about 160 mg of calcium in a cooked cup. With a bioavailability of 50%, about 80 mg is absorbed.
The amount of calcium absorbed in the body may differ between individuals, as the other foods eaten during the same meal as well as the individual’s metabolism may influence the amount of calcium that is absorbed.
Bone health is also protected by being active and exercising regularly, particularly weight-bearing exercises such as weight training, walking, and jogging.
Types of calcium supplements:
The two main forms of calcium supplements are:
- Calcium carbonate – the cheapest and most widely available form of calcium, which should be taken with food for optimal absorption.
- Calcium citrate – contains less elemental calcium but is more easily absorbed and can be taken with or without food. Although it is more expensive, it is recommended for people with irritable bowel syndrome or who are taking medication for acid reflux.
Conclusions:
While many people take calcium supplements with the aim of strengthening their bones, the amount of calcium adults need is still being debated. Harvard takes a critical view of the calcium debate and says the value of exercise and reversing vitamin D deficiency are more important for bone health, also saying there is little evidence that a high intake via supplements has more than a marginal effect on bone density and the prevention of fractures.
Another word of warning is that calcium supplements may interfere with the way your body processes certain medications, such as antibiotics and iron.
Obtaining calcium through your diet is the best source of calcium. Calcium supplements in moderation may benefit people who are not getting enough from their diets or those who are older, such as women who have reached menopause.
As some health risks are associated with excessive amounts of calcium, it is important to obtain medical advice on what’s right for you and to see if you really need supplements.
References:
Calcium supplements: Should you take them? Published online. Johns Hopkins Medicine. (www.hopkinsmedicine.org)
Calcium supplements may damage the heart. Published11 October 2016. Johns Hopkins Medicine. (www.hopkinsmedicine.org)
What you need to know about calcium. Published 13 October 2020. Harvard Medical School. (www.health.harvard.edu)
Calcium supplements: Should you take them? Published 22 October 2016. Healthline. (www.heaalthline.com)
Moderate calcium intake not linked to coronary artery calcifications says UAB cardiologist. Published 17 October 2016. News Medical Life Sciences. (www.news-medical-net)
Calcium. Published online. Harvard T H Chan School of Public Health. Harvard Medical School. (www.hsph.harvard.edu)
Calcium and calcium supplements: Achieving the right balance. Published 14 November 2020. Mayo Clinic. (www.mayoclinic.org)
The benefits and potential risks of calcium supplements. Published 23 July 2021. American Academy of Anti-Aging Medicine. (www.blog.a4m.com)
How much calcium do you really need? Published 11 September 2019. Harvard Health Publishing. Harvard Medical School. (www.health.harvard.edu)
Calcium supplements: A risk factor for heart attack? Published online. Mayo Clinic. (www.mayoclinic.org)
Calcium blood test. Published 24 January 2019. Healthline. (www.healthline.com)
HEALTH INSIGHT
September 2021