In October 2010, I included a section of my newsletter entitled Calcium: Friend or Foe? In response to inquiries about the potential hazards of supplemental calcium, I reviewed the literature and concluded that calcium was beneficial. In the last two years, more studies have been published building a convincing case that supplemental calcium may increase the risk of heart attacks and strokes. In fact, I am now recommending that you minimize or eliminate your ingestion of calcium supplements!
I am well aware of the potential for "health advice whiplash," rapidly switching from strongly supporting taking calcium supplements for bone health to trying to eliminate it due to risks to the brain and heart. Nonetheless, I am compelled to "First do no harm." In explanation, I will review what the most current studies are telling us. What the data tell us about how calcium may function in our bodies. How to balance the risks and benefits of calcium supplements. And, finally, how to maintain healthy bones while reducing the need for calcium supplements.
The results from the largest and most current study, EPIC-Heidelberg, appeared in the Journal Heart in late May 2012. This study followed almost 24,000 Europeans, ages 35-64 years old for an average of 11 years. Detailed dietary information was obtained at baseline and health outcomes were recorded. During the study, 354 heart attacks, 260 strokes and 267 cardiovascular deaths occurred. The researchers were able to analyze calcium intake and calculate the risk for these bad outcomes. The most striking finding — compared to those who never took calcium supplements, those that did had almost twice the risk of having a heart attack! The study further analyzed the risk according to how people obtained the calcium in their diet. Those who had less overall calcium (820 mg a day) mostly from dietary sources had a approximately 30% reduction in heart attack risk compared to those with very low calcium in their diet. The study presents an apparent contradiction – calcium supplements raise the risk of heart attack while calcium from dietary sources are protective.
The leading explanation for this contradiction focuses on how the calcium is absorbed into the body. When we eat calcium contained in food, its absorption is slowed by the protein and fat ingested with it. The level in the bloodstream probably remains fairly constant. When a calcium supplement is ingested a large amount of calcium is released rapidly potentially leading to a spike in the amount of calcium in the blood stream. These peaks in calcium concentration are thought to accelerate atherogenesis, "hardening of the arteries." This theory is supported by other studies documenting increased coronary artery disease in other patients with diseases or treatments that raise blood calcium levels, such as kidney failure patients.
The National Osteoporosis Foundation has issued a recent statement attempting to balance the risks and benefits of calcium supplements: http://nof.org/sites/default/files/pdfs/BoneBasicsAlert_CalciumBasics_2012.pdf
I agree with their advice to maximize your dietary intake of calcium, calculate your estimated daily intake of calcium and then use the smallest amount of calcium supplements to reach your recommended levels. The current Recommended Dietary Allowances (RDA) for non-pregnant adults are 1000 mg per day. Men over 70 and women over 50 require 1200 mg per day. Dairy products are a rich source of calcium, for example an 8 oz glass of milk contains 300 mg of calcium. However, many adults are lactose intolerant, ranging from 10-85% depending on the ethnic group. These individuals lack the enzyme lactase required to digest lactose, the naturally occurring sugar in milk, and can suffer from bloating and discomfort when consuming certain dairy products. A much rarer form of dairy intolerance is an allergy to protein in the cow’s milk, thought to affect less than 1% of the population. Those with lactose intolerance may tolerate certain dairy products that are low in lactose, such as yogurt or aged cheeses. Also, lactaid supplements that contain the enzyme lactase may enhance dairy product digestion. Those with a true cow’s milk allergy may be able to tolerate goat’s milk products which have different proteins. Non-dairy products that are rich in calcium include, broccoli, tofu, salmon and sardines. The NIH provides a very informative fact sheet about calcium, including nutritional information: http://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
I am well aware that advising you to reduce or eliminate calcium supplements may cause anxiety and confusion. At this point, there is not a consensus within the medical community about this issue. I believe that the most recent EPIC-Heidelberg study, in addition to recent studies in the last two years, provides a convincing case regarding the potential dangers of calcium supplements. Please see the recent New York Times article:
I personally have markedly reduced my intake of calcium supplements and feel compelled to recommend the same for my patients. I suggest reading the National Osteoporosis Foundation and NIH calcium factsheets to learn more about dietary sources of calcium. We can work together to find a safe and effective way to get the calcium you need!!