Calcium is the most abundant mineral in the human body. Bones and teeth comprise approximately 99% of total body calcium. The other 1% is distributed within cells and in the extracellular fluid. Although it may seem insignificant, this 1% must be carefully maintained in order for the body to carry out complex biochemical and physiological processes, including nerve conduction, muscle contraction, enzyme regulation, blood clotting, and control of blood pressure. Calcium Sources: Absorption and Bioavailability
Calcium is the most abundant mineral in the human body. Bones and teeth comprise approximately 99% of total body calcium. The other 1% is distributed within cells and in the extracellular fluid. Although it may seem insignificant, this 1% must be carefully maintained in order for the body to carry out complex biochemical and physiological processes, including nerve conduction, muscle contraction, enzyme regulation, blood clotting, and control of blood pressure.
Calcium Sources: Absorption and Bioavailability
Calcium can be found in a variety of foods, including dairy, green leafy vegetables, and fortified products such as orange juice. Despite the availability of calcium, millions of Americans don’t come close to meeting their daily requirement for calcium. In addition, 30 to 50 million Americans suffer from lactose intolerance. This condition makes it very difficult to consume regular dairy foods, one of the best sources of calcium.
To ensure adequate calcium intake, calcium supplements are a convenient and inexpensive option. Several forms of calcium supplements exist, with calcium citrate (organic salt) and carbonate (inorganic salt) being the most popular. Absorption of calcium can be affected by a variety of factors, making your choice of supplements an important one.
Researchers at the University of Texas Southwestern Medical School determined that calcium citrate is better absorbed than calcium carbonate by approximately 22 to 27%, either on an empty stomach or when co-administered with meals.(1) Despite having a higher percentage of elemental calcium, calcium carbonate may be poorly absorbed, especially in individuals with low stomach acid.
Prescription drugs such as H2 blockers (e.g., Tagamet) and proton pump inhibitors (PPI) (e.g., Prilosec) are among the most commonly prescribed drugs for heartburn or GERD (Gastroesophageal Reflux Disease), ulcers, and other stomach-related disorders. By reducing hydrochloric acid production/secretion by gastric parietal cells, these drugs may significantly reduce the dissolution and ionization of calcium. The result is a reduction of calcium absorption in the small intestine.
A 2006 study published in the Journal of the American Medical Association showed that long-term PPI therapy, particularly at high doses, is associated with an increased risk of hip fractures.(2) In addition, atrophic gastritis, gastric surgery, and high-dose, long-term use of antisecretory drugs markedly reduce acid secretion and may, therefore, increase the risk for malabsorption of dietary and supplementary calcium-thereby increasing the risk of osteoporosis in the long term.(3) In general, studies show that both calcium carbonate and calcium citrate can be effective, but given the many factors that influence calcium absorption, calcium citrate might be a better choice.
Clinical Data: Calcium and Vitamin D
Numerous studies demonstrate a protective role of calcium in helping reduce the risk for bone-related disorders, including osteoporosis and fractures. In a recent meta-analysis of 15 randomized trials conducted over the last 20 years, researchers suggested that calcium supplements increase the risk of heart attack by about 30%.(4) The specific studies selected as part of the meta-analysis by the authors didn’t actually measure cardiovascular endpoints. In order to gather this data, the authors, in some instances, had to go back 10 to 20 years from the date of the study to collect the necessary data. The authors stated, “None of the trials had cardiovascular outcomes as the primary endpoints, and data on cardiovascular events were not gathered in a standardized manner.” In addition, none of the studies included data on vitamins D and K.
One cannot discuss calcium without mention of these synergistic nutrients. Vitamin D, which in its active form (calcitriol) is actually a hormone, has been found to be deficient in close to 50% of the American population. This nutrient is critical for calcium absorption, reduced calcium loss via the kidneys, as well as reduced parathyroid hormone secretion-a hormone that leads to the breakdown of bone to help increase blood calcium levels. The study participants for which data was evaluated were in fact shown to have low levels of vitamin D, which when combined with calcium, has been shown to help improve total bone-mass density.(5) The rigorous Women’s Health Initiative, which included 27,000 subjects, showed that individuals taking calcium and a low-dose vitamin D supplement tended to have a lower mortality(6) and no adverse effects on cardiovascular health.(7)
The past few years has seen a significant increase in the research on vitamin K, particularly K2. Vitamin K2 has a much longer half-life than K1, resulting in much higher blood levels and demonstrating a greater ability to carboxylate (activate) osteocalcin, an essential calcium-binding protein.(8) Matrix-GLA protein is one of the most potent inhibitors of vascular calcification and arterial plaque stabilization. The activity of this important protein is highly dependent upon vitamin K.(9) Matrix-GLA protein helps keep calcium where it belongs-in the bones and out of the arteries.
Calcium has many years of clinical success supporting it as an important cofactor for building healthy bones. We can’t allow one meta-analysis to vilify an essential nutrient and discourage those individuals currently taking calcium and/or those considering it for osteoporosis risk reduction. Several studies have demonstrated the safety of oral calcium supplementation. Specifically, oral calcium supplements do not affect the progression of aortic valve calcification(10) and also do not increase cardiovascular disease and/or mortality in older women.(11)
The most important thing to keep in mind is that a nutrient, unlike a drug, doesn’t work alone. Each nutrient requires other nutrients and cofactors in order to carry out complex biochemical and physiological functions. It’s never a good idea to consume excess amounts of a single nutrient without considering the synergistic nutrients that work together to help promote optimal health.