Susan E. Williams

Calcium Primer: Current Controversies and Common Clinical Questions

The use of calcium supplements has recently come under fire because of studies purportedly showing a relationship to cardiovascular events. Although the conclusions made sensational headlines in the popular press, numerous editorials and convincing scientific evidence to the contrary went unnoticed. This controversy and others, such as the relationship of proton-pump inhibitors and osteoporosis, caffeine consumption and the risk of calciuria, and the effects of loop diuretics on fracture risk, are common clinical queries of both primary care physicians and subspecialists. The purpose of this article, therefore, is to provide a concise review of select literature pertinent to current clinical practice and to provide no-nonsense recommendations for common clinical dilemmas regarding calcium supplementation.

What Is Osteoporosis

The term “osteoporosis” has many meanings. Most clinicians tend to think that osteoporosis is a deficiency of bone mineral as reflected by a low bone density test or T-score. A more exacting definition, however, is that it is a disease which increases the risk for fragility fracture due to micro-architectural changes in bone. The challenge with the first definition is that osteoporosis can be present despite normal or near-normal bone density tests. The challenge with the second definition is that it requires more clinical input and places the burden of diagnosis on the clinician and not the DXA results.

The DXA Report: What Every Referring Clinician Needs to Know

The report is the final sequence in the pathway of a patient’s bone density testing. After the technologist performs the test, the results are interpreted and a written report is generated by a clinician. The quality of the report can vary widely due to a lack of historical patient information and the fact that some “interpreters” simply pass on the data generated by the DXA computer and provide no clinical assessment or interpretation.

Monitoring Treatment Efficacy: DXA Pearls and Pitfalls

One of the benefits of DXA is the ability to monitor the efficacy of therapies aimed at stabilizing and/or increasing bone density. Clinical trials in the development of drugs for osteoporosis have shown that increased bone density equates to reduction in fractures. It follows then that practitioners see increases in bone density as a surrogate marker for treatment success.

What Happens After I Order a DXA

In a recent survey of our primary care colleagues that asked “what would you like to know about DXA,” two very common themes were the request to learn more about the process and what to tell patients ahead of time. This chapter is dedicated to exactly that, provides an example of simple pre-DXA instructions, a pre-DXA questionnaire, and a step-by-step look into the process of obtaining bone mineral density measurements (Fig. 3.1).

Special Considerations in Common GI Diseases, Obesity, and Following Bariatric Surgery

Contrary to popular belief, obesity is not good for bones nor is it protective against the development of osteoporosis. Common consequences of obesity such as type 2 diabetes mellitus, and several of the common medications used to treat elevated blood glucose significantly increase the risk of osteoporosis and fragility fracture.

Introduction – How does one go from bone mineral density measurements to a diagnosis of osteoporosis

Bone mineral content (BMC) is a measure of the mineral found in bone. Bone mineral density (BMD) is a mathematical ratio of the measured mineral content in a de fi ned area of bone. The measured BMD is not a true cubic density. Other densities within and around a bone and the area of bone measured can affect the accuracy of the BMD.

What Is FRAX

As noted in the chapter about diagnosing osteoporosis (see Chap. 1), T-scores alone may not be adequate to predict the risk for fragility fractures and diagnose the disease state of osteoporosis because bone density testing only partially explains the risk for fracture. A large part of resistance to fracture or bone strength is related to elements comprising the quality of the skeleton which bone density cannot measure. These characteristics are related to a patient’s age and the microscopic architecture in the bone which are “hidden” from scanning. For the practitioner, these characteristics can be determined from a patient’s age and pertinent historical information.

UFOs: Unexpected Foreign Objects

As discussed in previous chapters, DXA testing relies on energy passing through living tissue, and the extent that the material is transparent or opaque to this energy estimates the amount of bone present. It should come as no surprise then to realize that any object incidentally found in or near the region of interest can add its “density” to a measurement, make the BMD result higher, and produce a false bone density reading. Usually the final measurement is better than expected, but not always.

Bariatric Surgery and Its Effects on Calcium and Bone Metabolism

The prevalence of obesity in the United States rapidly reached pandemic proportions during the second half of the twentieth century. Paralleling the pandemic, surgical treatment approaches came into vogue, stemming at least in part from the fact that patients who had undergone intestinal resection experienced significant and durable weight loss. Recent data from the American Society for Metabolic & Bariatric Surgery noted that the number of bariatric surgeries performed in the U.S. rose from 13,365 in 1998 to an estimated 220,000 in 2009, and has continued to rise. Documented nutritional ‘disturbances’ and weight loss following resection of major portions of the small intestine began to emerge very early in the twentieth century. J. D. Whitall in his 1911 paper examined outcomes involving various lengths of intestinal resection and concluded that the patient’s prognosis hinged upon several key factors, not the least of which was the location of the portion removed. Two decades later publications started to emerge that documented profound cases of hypocalcemia, tetany, and osteomalacia following massive resections of small intestine. It is pure speculation as to if an ‘‘Aha moment’’ occurred leading up to the first surgeries exclusively to treat obesity. However, in the United States during the 1950s, bypass surgeries known as ‘intestinal short circuiting’ were being investigated. The earliest bariatric procedures bypassed a great deal more of the small intestine than modern day procedures and did indeed result in dramatic weight loss but were accompanied by severe diarrhea, electrolyte imbalance, hepatic failure, and a high rate of mortality. Since that time myriad advances in the field of bariatric surgery have addressed many of the more serious postoperative metabolic complications and today there are several safe, effective bariatric procedures. However, the untoward consequences of malabsorption and dramatic weight loss on skeletal health persist to the present day. In this edition of CRBMM our authors present current knowledge in this unique field and discuss what is known as well as what remains unknown in the understanding, diagnosis, prevention, and treatment of metabolic bone disease in this population. An historical overview sets the stage for this edition, highlighting fundamental discoveries that began to link extensive gut loss to the dire consequences of metabolic bone disease. This article is followed by an excellent discussion by Jacqueline Center’s group exploring not only the limited evidence regarding the mechanisms of increased bone turnover but also some of the technical challenges of measuring bone during periods of severe weight loss. Peters et al. define known risk factors for secondary hyperparathyroidism in this population and discussed the benefits as well as the limitations of preventive strategies that include adequate dietary protein. Pramyothin and Holick explain the relationship between obesity and vitamin D deficiency, how weight loss affects 25-hydroxyvitamin D levels, and why despite massive weight loss, aggressive supplementation remains the mainstay of treatment. Finally, Sakhaee provides a detailed review of current knowledge of post bariatric surgery bone changes including mechanisms of bone loss and the role of calcitropic hormones. The high prevalence of hyperoxaluria, renal stone S. E. Williams (&) Department of Endocrinology, Diabetes and Metabolism, Cleveland Clinic, 10685 Carnegie Avenue/X-20, Cleveland, OH 44106, USA e-mail: WilliaS9@ccf.org