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Calcium: No bones about it

Matthew Barreau provides an in-depth review of calcium supplementation and the potential effects on the body

Most commonly associated with bone structure, calcium actually plays several other key roles within the body: it is required structurally in bones and teeth, used in both growth and repair; is an intracellular regulator, including keeping your muscles and heart functioning; keeps blood working correctly; maintains nerve function; is a cofactor for many proteins and enzymes, including blood clotting; preserves cell membrane permeability[11,13,14,20,35]. With 99% of the body's calcium being stored within the bones[13,29] they deservedly receive the most attention with regard to this mineral. The most common concern when it comes to calcium is with regard to osteoporosis, which is caused by a weakening of bones. This is a problem that is unique, as calcium is the only nutrient whose storage form serves as a functional role[35]. Bones are dynamic in that they are constantly changing; they respond to mechanical loading, hormonal fluctuations, and nutritional status. They are constantly breaking down and replacing and repairing themselves, based on the situations within the rest of the body[14]. When vital functions (i.e. heart and nerve function) become deficient in calcium caused by inadequate intake of the nutrient, the storage is tapped into and bones are subsequently weakened.

While this can occur daily, it is in the long run that this becomes an issue, as weakened bones can lead to osteoporosis[11,34]. Getting enough calcium can help reduce the risk of osteoporosis, but is not the only factor in thwarting bone problems. With its many functions within the body, it deserves special attention as a part of a well-balanced diet. This article will attempt to address any concerns related to calcium, and their potential effects on the body and calcium levels.

Forms and side effects

Calcium is available in many different forms, including calcium carbonate, calcium citrate, and in food products. Many people are looking to take supplements in order to get their daily calcium[9]. In considering calcium sources, cost and effectiveness are major components in making a decision on what source will be best. This portion of the report examines each of these forms, and presents some cautions when choosing certain ones.

Calcium carbonate

The most commonly found form of calcium in supplements is calcium carbonate. In fact, 85% of all calcium supplements sold in the US are made from calcium carbonate. As the least expensive and most highly concentrated of the supplements, it is easy to see why[4,7,8,9]. Additionally, the calcium from this form is absorbed well in the majority of the people who take it[4]. Stomach acid actually plays a role in calcium absorption, and therefore it has been found that calcium carbonate is best absorbed when taken with a meal. One of the most commonly found forms of calcium carbonate is Tums, which is commonly known as an antacid. This seems contradictory - taking an antacid with calcium, when acid helps absorption rates. However, it has been shown that when taken with a meal, stomach acidity levels are still sufficient enough to aid in calcium absorption[4,8].

Calcium citrate

Calcium citrate is the second most common form of supplement used. Unlike calcium carbonate, it has been shown to be best absorbed when taken without food. In situations where no stomach acid is present (i.e. people on ulcer medication), calcium citrate has been shown to be absorbed better. However, this difference seems to be less relevant if the calcium carbonate is taken with food. Both forms have been shown to be equally effective in healthy people, and appear to be as well absorbed as calcium from natural sources such as milk[9]. A drawback to calcium citrate can be the price, as it is less concentrated than calcium carbonate (less elemental calcium). But a potential benefit can be that calcium citrate can be absorbed better in the absence of food, since both carbonate and citrate have been shown to partially inhibit iron absorption if taken with food[9]. Therefore, if supplementing an iron-containing meal with calcium, it may be wise to choose citrate, and to not take it near the meal. However, if iron consumption is adequate, this should not be of a major concern, and the cost/effectiveness should be considered first.


When choosing a calcium source, cost per elemental calcium content, ease of use and convenience, and tolerability should be considered first. On each of these accounts, calcium carbonate scores very well[4]. Both calcium carbonate and citrate are extremely safe in men and women of all ages in supplementing daily calcium intake up to 2000mg a day[9].

While some studies have shown that calcium citrate can have a higher rate of absorption based on urinary excretion of calcium, others measuring actual fractional absorption of calcium from various sources (carbonate, citrate, and food sources) have found equivalent absorption[9]. A study in the New England Journal of Medicine also suggested that choosing one form over another based on absorption rates was not the way to go. The study found that when fasting, healthy, young volunteers were given equivalent amounts of calcium from various sources, the amount of calcium absorbed was very similar[4].

While any form of calcium will be effective, it will only be effective if it is taken. If the daily values cannot be obtained within the daily diet, then supplementation should be considered. As it has been described that absorption rates may not be a factor, then price alone would lend itself to choosing calcium carbonate. If absorption is a factor, then when taking supplements with a meal (since it is easiest to remember to do so at this time), carbonate is also the primary form, as it is better absorbed at this time[9].


Calcium supplements are well tolerated and the occurrence of significant negative effects is highly unusual[6]. One of the most common side effects when beginning calcium supplementation (by any form) is bloating or constipation, and is usually temporary as the body is merely adjusting to the new regiment of supplementation[6,9]. Calcium citrate has been shown to cause more bloating[9]. By taking supplements throughout the day, absorption can be increased while limiting gastrointestinal discomfort. Consuming more water can also reduce constipation[6]. One study comparing the gastrointestinal tolerability of calcium carbonate, calcium citrate, and calcium phosphate showed that all three were well tolerated compared to placebo. The only difference was slightly more bloating with calcium citrate. The reported incidence of bloating, gas, or constipation with calcium carbonate was equivalent to, or less than, placebo[6]. The side effects may not be caused by the calcium itself, but may be due to other ingredients in the supplements. Because of this, consumers should look for the USP mark on the label.

This means that the products have been tested and meet the standards of purity and effectiveness set by the United States Pharmacopoeia [6,7,9,11]. Most major brands of calcium, such as Tums, carry the USP mark[7]. Additional concerns with calcium supplements are related to the lead content. A naturally occurring mineral found in fruit, vegetables, and dairy products, lead can be harmful if consumed in large amounts. Supplements typically contain less lead than many dairy and vegetable food sources; 1000mg of elemental calcium supplementation means absorption of about 0.25mcg of lead, far below the FDA's acceptable intake of 75mcg per day. Also, calcium blocks absorption of lead by the body. Lead and calcium are absorbed at the same site in the intestine, and this site prefers calcium. The more calcium the body gets the less lead it is able to absorb, and it is eventually excreted out of the body[7].

How to get it

Many nutritionists are advocates of obtaining your daily amounts of calcium through food products, and only using supplementation if required. No-fat or low-fat dairy products are the most plentiful sources of calcium in the diet. For those who are lactose intolerant, soy products have been suggested as a good alternative. Broccoli, kale, dried fruit, and salmon still containing the bones are also good sources. Many foods now are being fortified with calcium due to its importance[11,12,13]. Multi-vitamins can give you calcium as well as other nutrients and vitamins your body may need, and are therefore a good choice. It is important to check the amount of elemental calcium in whatever supplement you take, though. Look for mg of elemental calcium, rather than percentages of daily values. The National Osteoporosis Foundation has recommended Tums as an excellent source of calcium. Since it is calcium carbonate, remember to take it with a meal for best effectiveness[11].

However you choose to get your daily dose, just make sure you get it.

Vitamin D and other helpful nutrients

Calcium does not work on its own; it requires other things to help it be absorbed or used within the body. At the same time, there are some things that hamper the body's ability to utilize the calcium that it receives, thereby putting bones at an increased risk for problems[33]. This section of the article takes a deeper look into the interactions of calcium with other things that may be found in the diet.

Vitamin D

Although nutrients such as iron, sodium, oxalate and magnesium may influence calcium's effectiveness, vitamin D is the most important additional nutrient shown to enhance calcium's ability to build and maintain bones[5,25]. Vitamin D is naturally produced by the body as a response to the sun[1,5]. In fact, only about 15 minutes a day in the sun can produce the body's daily need of the vitamin[11,33]. Most Americans do not need to worry about a lack of this vitamin, because it is so easy to obtain through fortified foods and by small amounts of sun exposure[5]. The recommended amount of vitamin D is 400 to 800 International Units (IU] per day, with higher amounts recommended for the elderly or those who do not receive much sunlight[5,26,34].

Some calcium supplements contain vitamin D, and most multivitamins will contain a daily dose of it[26]. Milk and other fortified dairy products, breakfast cereals, fatty fish, and cod liver oil are also good sources of vitamin D. And while vitamin D is required for the body to absorb calcium[1], it is not required to take it in conjunction with calcium. This is because the body can store vitamin D in the liver for extended periods of time. However, additional vitamin D increased the short-term absorption of calcium even in healthy individuals with no apparent vitamin D deficiency[5,11]. Vitamin D supplementation alone may not be effective, according to at least one study[29]. It showed that calcium supplementation (1200mg) in combination with vitamin D in physiological doses reduced the incidence of hip fractures in institutionalized patients older than 75, but vitamin D alone did not.

Vitamin D depletion has been shown to result in a decrease in membrane calcium transport[31], indicating that the role of the vitamin extends beyond just the uptake and absorption of calcium. One potential drawback to vitamin D supplementation is that it can cause calcium deposits in the heart. Estrogen can protect against this[27].

Other good things

Phytoestrogens are plant chemicals that are responsible for estrogen-like effects on the bone. They can be found in legumes, cereals, nuts and berries, as well as soybean and soy products. Phytoestrogens have become the buzz of late as a "natural medicine" alternative to HRT. A couple studies have given backing to this school of thought. One showed that a soy protein-enriched diet prevented bone loss at the femur and spine in rats. Another followed 187 postmenopausal women for six months, splitting them into three groups: 1) HRT, 2) soy-based foods, or 3) no treatment. Only in the control group was there a significant drop in trabecular bone mineral density. It should be noted, however, that there are only a limited number of studies on this, and that no definite conclusions can be drawn regarding the relationship between phytoestrogens and bone health[29].

Milk, aside from containing vitamin D, also contains the sugar lactose, which also helps the absorption of calcium in the intestine[33]. This gives extra credence to the recommendation that people get their calcium from natural sources, especially dairy products. Getting calcium from milk rather than supplements allows the individual to receive more calcium per swallow. Those who are lactose intolerant should try using a lactose replacement product such as Lactaid or Dairy Ease to combat their tendency to consume less calcium and have less dense bones. Also, the protein sparks stomach acid secretion, which also helps calcium absorption reach peak levels[33].

Other elements that have beneficial effects on calcium absorption include fluoride, magnesium, copper, zinc, magnesium, silicon, riboflavin, iron, and boron. Fluoride is typically contained in city water, and a diet consisting of seafood, fruits, vegetables, whole grains, beans, nuts, and seeds will provide the rest of the nutrients. This is especially important for those not getting 2 to 3 servings of dairy products a day[33, 35].

Bad things

With the good, also comes the bad. Several things can adversely affect bone health and calcium uptake. These seemingly simple things can very quickly reverse the hard work people put in to take care of their bones. While there is no convincing proof that caffeine adversely affects bone mass in those with adequate calcium intake, a couple recent studies found that intakes of caffeine-rich beverages were associated with greater bone loss at the spine and with a moderately increased the risk of fractures[29]. The caffeine in one cup of coffee (150mg) can increase calcium needs by 30 to 50mg a day[33]. Smoking increases the loss of calcium from the body, along with alcohol, which also decreases calcium absorption and can suppress bone formation[29, 32, 33]. Alcohol can also increase calcium losses[33].

While eating a balanced diet was recommended above, it must be noted that eating too much can be detrimental. Eating too much protein (twice the RDA) may cause your body to lose calcium. Foods that are high in fibre bind with calcium and keep it from being absorbed. Additionally, excessive intakes of certain minerals such as zinc can decrease calcium absorption. The aluminium hydroxide in some antacids also increase bone calcium loss and calcium excretion[33]. High intakes of salt also increases the amount of calcium lost in the urine[29, 33].


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Article Reference

This article first appeared in:

  • BARREAU, M. (2005) Calcium: No bones about it. Brian Mackenzie's Successful Coaching, (ISSN 1745-7513/ 24 / July-August), p. 4-7

Page Reference

If you quote information from this page in your work then the reference for this page is:

  • BARREAU, M. (2005) Calcium: No bones about it [WWW] Available from: [Accessed

About the Author

Matthew Barreau is assistant Cross Country and track coach in charge of distances at Portland State University, a USATF Level II certified Endurance Coach and a USATF Level II certified Sprints/Hurdles/Relays Coach.

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