Calcium -- The Food Versus Supplement Debate - Food for Thought - Harvard Commentaries

Calcium is well known for its role in building and maintaining strong bones and teeth. It also functions in blood clotting, nerve conduction and muscle contraction. There is preliminary evidence that calcium supplementation may decrease blood pressure, colon-cancer risk, and symptoms of PMS.

It is best to try to meet calcium needs with food sources. For those who find it difficult, calcium supplements are helpful, but not all supplements are equal. The following are some of the most common questions nutritionists are asked about calcium supplementation, and our answers.

Dairy provides rich, natural sources of calcium and is the major contributor of dietary calcium intake in the United States. But for those who cannot tolerate dairy, are lactose intolerant, or simply don't like the taste of milk-based products, other food sources of calcium are available. The list includes certain vegetables, beans, nuts and soy. Products such as fruit juices, non-dairy drinks, tofu and cereals have now been fortified with calcium.

Calcium supplementation has been a standard of care for the prevention and treatment of osteoporosis. According to NHANES 2003-2006, about 43% of the U.S. population (with almost 70% as older women) uses dietary supplements containing calcium.

But new research from Europe questions the safety of this widespread practice. A study recently published in the journal HEART found that individuals who took calcium supplements had a higher risk of heart attack compared to those who did not take calcium supplements. The risk was greater in people who took only calcium supplements and no other supplements.

The findings of this study are consistent with the results of a New Zealand meta-analysis, which first suggested a possible link between calcium supplements and cardiovascular disease risk 2 years ago. Using data from the Women's Health Initiative Calcium/Vitamin D Supplementation Study (WHI CaD Study), the authors found that calcium supplements, whether with or without vitamin D, increased the risk of cardiovascular events, particularly heart attack. Furthermore, when comparing the benefits of calcium supplementation on fracture prevention with the risk of cardiovascular events, the risks outweighed the benefits. In their analysis, they concluded that for every 1,000 patients treated with calcium or calcium with vitamin D for 5 years, 6 more myocardial infarctions or strokes would occur and only 3 fractures would be prevented.

With the widespread use of calcium supplements, this modest increase in risk of cardiovascular events may translate to more disease, particularly among older people. We many need to re-evaluation the role of calcium supplementation in the prevention and treatment of osteoporosis.

There is also another reason to be cautious about calcium supplementation. Kidney stones in the urinary tract are commonly made from calcium oxalate. Some studies suggest a positive association between supplemental calcium intake and kidney stone formation. In the Women's Health Initiative study, postmenopausal women who took 1,000 mg of calcium with 400 IU of vitamin D for 7 years had a 17% greater risk of developing kidney stones than participants who were given a placebo.

The research suggests that the sudden rise in blood calcium levels after supplementation may be the driving force for increasing cardiovascular disease risk. Observational studies have linked increased blood calcium levels with higher heart attack rates. When calcium builds up in the blood it can lead to plaque in the arteries. Plaque is a precursor to atherosclerosis and other cardiovascular disease.

The good news is that calcium-rich foods do not have the same effect. Dietary calcium enters the bloodstream slowly, causing a more gradual rise in serum levels.

The good news also extends for calcium-rich foods and kidney stone formation. In fact, higher intakes of dietary calcium might actually protect against developing them.

The body can absorb about 500 mg of calcium at one time. Therefore it is best to spread your intake of calcium-rich foods throughout the day.
Vitamin D enhances calcium absorption. Make sure to maintain optimal vitamin D blood levels. This can be done through diet, supplementation and appropriate sun exposure.
Oxalic and phytic acids found in whole grains, dark leafy vegetables, peanuts and soy beans decrease the absorption of calcium in these foods.
Phosphoric acid in dark sodas can interfere with your body's absorption of calcium.
Prolonged use of magnesium-containing laxatives reduces calcium absorption.
Caffeine increases calcium lost in the urine. Limit yourself to 1 to 2 cups of caffeinated coffee, soda or tea per day.
Excess sodium in the diet also increases calcium excretion. Every 500 mg of sodium over 2,400 mg per day causes the body to lose 10 mg of calcium.
As you age, your body absorbs less calcium. That's why the recommended intakes of calcium are higher for older adults. See the table above for the RDA for your age group.
Maintaining a healthy weight, performing resistance training at least twice per week, and not smoking are important for good bone health.

Calcium is needed for healthy bones, teeth, nails and muscle tissue. It also helps in blood clotting and heart and nerve functions. Calcium supplements have uncertain benefits and possible risk of cardiovascular disease. So it's best to get your calcium through food. However, certain circumstances may warrant the need for calcium supplementation. It is important to speak to a doctor, pharmacist, or nutritionist before starting a calcium supplement.

Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.

U.S. Department of Agriculture, Agricultural Research Service. 2011. USDA National Nutrient Database for Standard Reference, Release 24. Nutrient Data Laboratory Home Page, http://www.ars.usda.gov/ba/bhnrc/ndl.

Kuanrong Li, Rudolf Kaaks, Jakob Linseisen, Sabine Rohrmann. Associations of dietary calcium intake and calcium supplementation with myocardial infarcation and stroke risk and overall cardiovascular mortality in the Heidelber cohort of the European Prospective Investigation into Cancer and Nutrition study (EPIC-Heidelber). Heart. 2012; 98:920-925.

Bolland MJ, Grey A, Avenell A, Gamble GD, Reid IR. Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women's Health Initiative limited access dataset and meta-analysis. BMJ. 2011 Apr 19;342:d2040.

Jackson RD, LaCroix AZ, Gass M, Wallace RB, Robbins J, Lewis CE, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med 2006;354:669-83.

Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med. 1997 Apr 1;126(7):497-504.

Curhan G, Willett WC, Rimm E, Stampher MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8.

Anne Chiavacci, R.D., M.S., M.A., is a senior nutritionist at Brigham and Women's Hospital and Dana-Farber Cancer Institute. She received her Bachelor of Science in nutrition from the University of Massachusetts at Amherst and her Master of Science in nutrition at Tufts University. Chiavacci completed her dietetic internship at Frances Stern Nutrition Center, New England Medical Center in Boston. She has a Master of Arts in counseling from the Biblical Theological Seminary in Hatfield, Pa.