Everything You Need to Know About Calcium

Calcium is required at every stage of life. It’s crucial starting in childhood when we really develop a solid foundation for healthy bones in the future. Throughout adolescence, bones grow rapidly. It’s also very important during pregnancy and lactation, as well as when one is healing from injuries. In later years, bones can begin to lose some of their sturdiness and strength, so a calcium-rich diet and supplementation become even more important. But with all of the options, it can be difficult to decide which type of calcium to take.

Some of the forms you’ll find on store shelves include: calcium carbonate, calcium citrate, calcium bis-glycinate, calcium citrate malate, calcium phosphate, calcium gluconate, calcium lactate, MCHC (microcrystalline hydroxyapatite), and others. Before choosing a type, there are several factors that need to be addressed. First, one should grasp the concept and importance of elemental calcium. Elemental calcium is the actual amount of calcium within the calcium supplement.

Looking at the differences between calcium carbonate and calcium citrate, there is more elemental calcium in calcium carbonate (40% elemental) than in calcium citrate (21%). A label may state 1,250 milligrams (mg) of calcium carbonate, which contains only 500 mg of elemental calcium. We can determine this because it is 40% elemental. This is important to note, because it can result in taking a lot of pills with the potential of absorbing little actual calcium into the blood stream.

Second, we need to look at solubility. Each form has a different degree of solubility and absorption. "Solubility” means the amount that can be dissolved in water at a neutral pH. If stomach acid levels are high, most forms of calcium are soluble. This is the case for most younger individuals, but as we grow older several issues can come into play (less stomach acid, acid-blockers) increasing the need for a more soluble form of calcium.

Third, it is important to remember that our body also needs other helper nutrients such as vitamin D, vitamin K, magnesium, and other minerals to better absorb any form of calcium. A more pH base intestine can interfere with calcium absorption, but vitamin D3, vitamin K2, and several other minerals increase intestinal absorption. All forms of calcium are absorbed best when taken with meals.

  • Calcium carbonate is the least expensive, and most commonly used calcium supplement. It contains about 40% of elemental calcium, which is almost twice the amount of other forms. It is an alkaline-based compound found in rocks, limestone, eggshells, etc. It has lower solubility and requires the production of extra stomach acid in order to be absorbed more effectively.
  • Calcium citrate has less elemental calcium (approximately 20-25%), but may be a better calcium supplement choice for people with reduced levels of stomach acid. Calcium citrate is different than calcium carbonate because it has an acidic base and does not require as much hydrochloric acid in the stomach to be absorbed.
  • When calcium is bound to glycine to form calcium bis-glycinate, it becomes an amino acid chelate. Amino acid chelates promote the assimilation of the mineral into the cells better for energy production.
  • Calcium citrate malate is created by mixing the calcium salt found in citric acid with malic acid. It has higher levels of solubility and absorption because it is water-soluble.
  • Calcium phosphate is the main form of calcium coming from cow’s milk. Tooth enamel and bones are very high in calcium phosphate. Calcium lactate is the form of calcium found in foods such as aged cheese and baking powder. Calcium phosphate, calcium lactate, and calcium gluconate have very small percentages of elemental calcium in each supplement tablet; therefore, it is necessary to take more tablets to achieve an adequate amount of calcium every day.
  • MCHC (microcrystalline hydroxyapatite) is quite unique. It is different than the others, as it’s a calcium-containing substance derived from whole bone. It provides organic constituents like protein and mineral and trace mineral components. It’s also quite absorbable.


The Recommended Daily Allowance (RDA) for daily calcium is around 1,000 mg for adults, with upper limits ranging from 2,000-2,500 mg/d. This amount should be the daily total coming from a combined food and supplemental source. Calcium supplements are available in a variety of forms, including tablets, capsules, chews, liquids and powders. So whichever form of calcium you choose, remember that all varieties of calcium supplements are better absorbed when taken in small doses of 500 mg or less at a time, during mealtime.