Calcium builds strong bones, and more is better–correct? Well, maybe not.
Calcium supplementation has been considered the gold standard therapy for osteoporosis in the general population. It is given in both the placebo and treatment groups of trials evaluating antifracture efficacy of new therapies. Similarly, calcium-based phosphate binders have been considered the gold standard comparator for all new phosphate binders. However, large randomized trials demonstrate conflicting data on the antifracture efficacy of calcium supplementation, particularly in high doses, in patients with osteoporosis without CKD. In addition, recent data suggest an increased risk for cardiovascular events. These new studies raise safety concerns for the general approach with calcium supplementation and binders. This review describes recent data on the adverse effects of calcium supplementation for osteoporosis and how these new data should affect the strategy for phosphate binder use in CKD.
It is important to note that some clinical practice guidelines have been modified on the basis of this new literature suggesting potential risk. For example, in its recently published evidence-based guidelines, Osteoporosis Canada recommended a total intake of calcium (from diet and supplement) of 1200 mg per day, a decrease from the previous recommendation of 1500 mg in supplements (32). The American Society for Bone and Mineral Research issued a statement regarding the potential risks of calcium supplements and suggested, among other points, that “the beneficial effects of calcium are found with relatively low doses. More is not necessarily better. Individuals should discuss the amount of their calcium intake with their healthcare provider” (33). The Institute of Medicine now recommends a daily dietary reference allowance of calcium of 1000–1200 mg per day in the form of diet and supplements (34,35). Finally, the draft United States Preventive Services Task Force statement, pending public comment (http://www.uspreventiveservicestaskforce.org/draftrec3.htm), currently states “the current evidence is insufficient to assess the balance of the benefits and harms of combined vitamin D and calcium supplementation for the primary prevention of fractures in premenopausal women or in men.” Thus, these authorities acknowledge that although some calcium supplements may be beneficial for bone health, too much calcium may be harmful.