Calcium is one of the main minerals of the body, constituting 1.5-2% of the body weight. The role of calcium in maintaining the health of bones, teeth and nails is well known. An adequate calcium intake helps maintain or improve bone mass, and decrease the risk ofosteopenia and osteoporosis. Calcium is also important for the functioning of heart, muscles and nerves. Calcium supplements have other health benefits as well, such as they decrease the risk of colorectal cancers and may help in reducing body weight and fat.
The recommended dietary allowance (RDA) for calcium in healthy adults is 1,000 mg/day (Indian Council of Medical Research recommends lower daily intake around 600 mg/day). Men older than 70 years, women older than 50 years and pregnant/ lactating women require higher amounts over 1,200 mg a day. Those with risk factors for osteoporosis such as postmenopausal women, smokers, people suffering from certain diseases (e.g. inflammatory arthritis, hyperthyroidism) and taking certain drugs (such as steroids, antiepileptics) need to pay particular attention to their calcium intake.
Any individual who is not able to meet his daily calcium requirements through diet should discuss with his/her doctor to consider starting calcium supplements.
It is best to meet the calcium requirements naturally through diet. Dairy products (milk, cheese, curd) are rich sources of calcium, as are some animal foods such as seafood (e.g. sardines). Plant foods have limited amounts of calcium, and only greens (e.g. broccoli, cabbage, mustard greens or sarson), nuts, dried beans, tofu, okra and some fruits (e.g. berries, kiwi, litchi, oranges) have significant amounts of calcium. Among grains, only amaranth (rajgira), a pseudocereal commonly used in Hindu fasts, contains good amount of calcium. Fortified foods such as oats, cornflakes, canned juices, etc. are good sources of calcium as well.
All calcium supplements or salts are not the same, and differ in the amount of available calcium in the salt (elemental calcium). The common calcium formulations used in supplements are calcium carbonate (containing 40% elemental calcium) and calcium citrate (containing 21% elemental calcium). Calcium formulations such as calcium gluconate (9% elemental calcium) and calcium lactate (13% elemental calcium) contain too low an amount of calcium to be useful.
The amount of elemental calcium in a supplement is mentioned on the insert and should be checked. 500 mg elemental calcium is optimum for supplementation in one dose, as higher amounts don’t get absorbed properly. One 1250 mg tablet of calcium carbonate, or two 1250 mg tablets of calcium citrate provide 500 mg elemental calcium.
Just the availability of calcium in a tablet is not enough; it must dissolve in the stomach and get absorbed in the body to act! The solubility of the tablet is usually regulated by manufacturing standards, but a quick test is to check whether a tablet dissolves in a glass of vinegar in 30 minutes (stirring intermittently). Calcium carbonate dissolves only in an acidic environment, and needs to be taken with meals, whereas calcium citrate can be taken irrespective of the timing of meals. People taking antacids should avoid calcium carbonate supplements for the same reason. Calcium phosphate is one formulation of calcium that has poor solubility, and hence is not commonly used in supplements.
The body absorbs only around 20-30% of the ingested calcium from most foods, though the extent of absorption varies with age (more in infants and less in elderly) and calcium intake (higher intake decreases absorption), apart from other factors such as vitamin D levels. Certain foods have substances that bind calcium and inhibit its absorption, such as caffeine in tea/coffee and oxalates in spinach. Calcium supplements should be avoided with such foods.
The amount of calcium absorbed from most calcium supplements (bioavailability) is similar or higher than that from foods. Only tricalcium phosphate has low bioavailability of all the common calcium formulations. Calcium citrate (particularly calcium citrate malate or CCM) has somewhat higher (40-50%) and faster absorption than calcium carbonate, but if the latter is taken properly with food, there is not much difference. Some formulations such as coral calcium (which is calcium carbonate only!) claim to have higher calcium bioavailability along with other health benefits, but such claims have been found to be misleading.
The dosage of calcium supplements is determined by the difference between the dietary intake and estimated requirements of calcium of an individual. It should be noted that the tolerable upper intake levels of calcium (beyond which there is potential for harm) are much higher than RDA, around 2000-2500 mg/day (see Table below).
Individuals with an estimated dietary intake of calcium less than 400 mg (e.g. people not taking dairy products altogether) can safely take 1,500 mg of calcium supplements (3 tablets of 500 mg calcium carbonate), whereas those with dietary calcium intakes between 400 to 800 mg (e.g. people taking a typical vegetarian or non-vegetarian diet with one serving of milk or other dairy product) should take 1,000 mg of calcium supplements. Individuals with dietary calcium intake between 800 and 1,200 mg can optionally take 500 mg supplements. Since the RDA for Indian population are estimated to be lower than international recommendations, Indians can take one 500 mg tablet less for each of the three groups mentioned above.
Though hypercalcemia (high calcium levels in blood) rarely occurs due to calcium supplements, a high serum calcium level in annual health check-ups should alert one to reduce the dose of supplements. Other safety issues with calcium supplementation can be due to adverse interactions with other medications and this should be discussed with the doctor e.g. calcium carbonate interferes with absorption of iron, and calcium and iron supplements should not be taken together.
Most calcium supplements are well tolerated, with minor side effects such as constipation and bloating. Constipation is more commonly seen with calcium carbonate supplements, and change of the brand or type of supplement should be considered, if one is not able to tolerate a calcium supplement. Strict vegetarians should check the package insert to check whether the supplement is made from animal sources such as oyster shells.
Apart from adverse effects, cost of the supplement also has a bearing on long term compliance and policy formulation. Calcium carbonate is the cheapest formulation of all, and is widely available from natural sources. Hence, it is the preferred form of calcium supplementation worldwide, both due to lower costs and higher elemental calcium.
Apart from short term adverse effects, there are some health concerns when calcium supplements are taken over a long period. Increase in blood calcium levels increases the urinary excretion of calcium too, potentially increasing the risk of renal stones, though such risk is not reported with dietary calcium. Most studies have not found any increased incidence of renal stones in people taking calcium supplements, but those with a history of renal stones should discuss this with their doctor. Calcium citrate malate has been found to be safer in such patients.
Cardiovascular effects of calcium supplementation are controversial. On one hand, calcium supplements have cardiovascular benefit as they are purported to decrease blood pressure, but on the other hand, increased calcium levels are thought to increase calcium deposits in arteries and increase the risk of heart attacks and strokes. Though the latter has not been conclusively proven in epidemiological studies, but there is consensus that calcium supplements have some adverse cardiovascular effects in the long run.
Bone health not only depends upon calcium, but also other nutrients such as vitamin D, phosphorus, magnesium, zinc, vitamin K2, etc. and these are frequently added to calcium supplements. Vitamin D is crucial for absorption of calcium from the gut, and is not present in most foods, being synthesized naturally in the skin on exposure to sunlight. With increasingly indoor lifestyles, vitamin D deficiency has become common in the population in subtropical and temperate climates such as India. Hence, vitamin D is an essential part of calcium supplements in such regions. The recommended dose of vitamin D is between 600-1,000 IU/day for adults.
Vitamin K2 (menaquinone) is one of the two naturally occurring forms of vitamin K and plays an important role in blood clotting, wound healing, bone mineralization, apart from its benefits for cardiovascular diseases and cancers. Like vitamin D, it too is present in only few foods (e.g. organ meats and fermented foods e.g. curd, cheese, beer, wine), and is synthesized (in small amounts) naturally by gut bacteria. Its deficiency is becoming increasingly common and thus, vitamin K2 (or its more readily absorbed subtype K2-7) is another common addition to calcium supplements.
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