While advocacy and health-policy making organizations cite evidence that calcium is necessary to build and maintain strong bones, a body of research continues to grow indicating this nutrient is ineffective when it comes to preventing fractures in older adults, and may, in fact, be dangerous at recommended levels. What accounts for such dramatically different conclusions? And what advice should nutrition professionals give their patients going forward?


Critical Calcium
Calcium is the most abundant and dominant mineral in the body. It's important for skeletal health, as well as a whole host of other essential functions.  Without calcium there would be no nerve transmission, muscle contraction, cell signaling, blood clotting, constriction and relaxation of blood vessels, or secretion of hormones like insulin.  If there isn't enough calcium coming in from the diet, the body will pull calcium from the bones for all of these things that need to be done.

The 2011 Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine (IOM) concluded that calcium plays a key cause-and-effect role in maintaining a healthy skeleton, and issued Recommended Dietary Allowances (RDAs) for all life stages over 1 year of age.  The report recommends that most adults aged 19 to 70 get a total of 1,000 mg of calcium daily, and women older than 50 and men older than 70 aim for 1,200 mg of calcium per day. The 2015 Dietary Guidelines Advisory Committee (DGAC) concluded that many Americans don't meet these recommendations, and declared calcium "a nutrient of public health concern for under-consumption."

While the IOM intends for RDIs to be met by eating a variety of foods as part of a regular diet, supplements often are seen as a way to ensure adequate calcium intake.  Many guidelines advise older people to get at least 1,000 to 1,200 mg per day of calcium to improve bone density and prevent fractures.  The average calcium intake in most countries is a lot less than these recommendations, and so many people take calcium supplements to increase their calcium intake. For example, in recent studies, more than 50% of older women in the United States took calcium supplements.


Conflicting Conclusions
In September 2015, BMJ published a study by Bolland and colleagues questioning the effectiveness of America's current calcium recommendations for protecting bone health. This meta-analysis of randomized controlled trials concluded there's "weak and inconsistent" evidence that calcium supplements prevent fractures. According to Bolland, the lead study author, "In 26 clinical trials, calcium supplements have only small, inconsistent benefits in preventing fractures, with no effect on fractures seen in the highest-quality trials.  In addition, in 59 randomized, controlled trials, we found that increasing calcium intake either from the diet or by taking calcium supplements led to similar, small increases in bone density of 1% to 2%. These increases do not build up over time and are too small to produce significant reductions in the chance of having a fracture." Bolland recommends against increasing calcium intake to prevent fractures except in frail, institutionalized, elderly women with low dietary calcium intakes and serum vitamin D levels.

Causes of the Confusion
There's a huge body of literature about the benefits and risks of calcium, much of which is inconsistent.  This has led to confusion and controversy.

Epidemiologic studies do not show cause and effect; they only find correlations that could be areas for future study.  Even meta-analyses can potentially be misleading, especially if they don't utilize all available studies.  Sometimes inconsistent or inaccurate results can come from not having enough studies to draw from, or from trying to compare studies that may have looked at an issue in different ways.  

Another possible factor confounding the data on the effectiveness and safety of dietary and supplemental calcium is the fact that calcium doesn't act alone on the skeleton. The interplay between vitamin D and calcium often is discussed, but many other nutrients are involved in calcium balance. According to the World Health Organization, a case can be made based on biochemical and metabolic evidence that zinc, copper, manganese, boron, vitamin A, vitamin C, vitamin K, the B vitamins, potassium, and sodium all may be involved in long-term bone heath and the prevention of osteoporosis. This means that the overall diet and nutrition status (and even genetic tendencies) of the study participants could be influencing the impact of calcium intake.  Moreover, since physical activity improves bone health, the varying activity levels of study participants also could affect outcomes.  


Clinical Implications
While the data are clearly inconsistent, there are certain points on which almost everyone agrees: Calcium is important for skeletal health; and calcium and vitamin D supplementation reduce fracture risk in frail, elderly women living in institutions.

The National Osteoporosis Foundation, the Institute of Medicine, and the Food and Drug Administration have all come out with guidelines and recommendations saying that calcium and vitamin D are clearly important for skeletal and other health. But how these recommendations are being implemented is shifting, with less emphasis being placed on calcium supplements and more on food sources.  The bottom line is that food trumps supplements.  In other words, dietary sources are preferred in terms of calcium intake.

In addition, recent concerns about the safety of calcium supplements have led experts to recommend increasing calcium intake through food rather than by taking supplements, even though the effect of increasing dietary calcium intake on bone health has not been clearly established.

Getting calcium from food can improve health in other ways.  Nearly three-quarters (72%) of calcium in the American diet comes from dairy foods. Dairy is also the No. 1 source of potassium in the American diet.  (Potassium is another nutrient identified by the 2015 DGAC as an under-consumed nutrient of concern.)  Shifting the focus to food first has other benefits as well.  Since bone health is impacted by more than just calcium, a well-balanced, healthful diet ensures intake of all the nutrients necessary for a strong skeleton.  Calcium is less bioavailable in plant sources than animal sources, but including plant-based sources of calcium such as dark leafy greens, broccoli, beans, tofu, and almonds increases calcium intake while adding to the healthfulness of the overall diet.  With calcium and vitamin D supplements, you're getting just those nutrients. From foods you get nutrients like potassium, magnesium, fiber, and phytochemicals that also play an important role in health.

Individuals should strive to meet the calcium levels recommended by the IOM, using food sources to the greatest extent possible.  Getting more than the recommended levels is not a good idea since there is the possibility of increased risk of kidney stones and other potential adverse effects.

The mixed messages on calcium recommendations are confusing to patients and clinicians alike.  Nutrition professionals are keeping a close, analytical eye on emerging research and continue to encourage patients to be physically active and to include cold water fish, dark leafy greens, tofu and other calcium sources like almonds and beans as part of a healthful, well-balanced diet.


Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer, a community educator, and the principal of JTRD Nutrition Education Services.