Nutrition & The
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605899_NMD05_sw 5/25/06 2:19 PM Page 1 Written for VOL. 32 NO. 5 the Professional by MAY 2006 the Professional Nutrition & the M.D.® Borrowing Against the Bones: 04/08/2021 on lMxUd3vOHJ2D2u3fSY5/nrpjSPd72SQCfmPJoWnzDe6u0qxpN2kmvD8jBPMGRRem7Bntg1Y0e9t7if5IUWHMKao2B3dxszzZO0dJ5WCMoV0LOTO7eYrUbAKxzK1elkfVtlTmkZ+Yx0Y= by http://journals.lww.com/clinnutrinsight from Downloaded Table 1. Physiologic Processes Dependent on The Price of Eucalcemia in the Calcium Downloaded Calcium-Deficient State Intracellular signal transduction (“second messenger”) from Neuronal transmission http://journals.lww.com/clinnutrinsight Jordan L. Geller, MD Dr. Geller is a practicing endocrinologist at the Cedars-Sinai Muscle function (linking excitation and contraction) Medical Center and a clinical instructor in endocrinology at Blood coagulation (cofactor for factors VII, IX, X, the UCLA School of Medicine, Los Angeles, CA. and prothrombin) Enzymatic cofactors by Learning Objectives: After reading this article, the lMxUd3vOHJ2D2u3fSY5/nrpjSPd72SQCfmPJoWnzDe6u0qxpN2kmvD8jBPMGRRem7Bntg1Y0e9t7if5IUWHMKao2B3dxszzZO0dJ5WCMoV0LOTO7eYrUbAKxzK1elkfVtlTmkZ+Yx0Y= participant should be able to: Cellular membrane and cytoskeletal integrity 1. State the mechanisms through which the body Hormone secretion (e.g. insulin) maintains calcium homeostasis. Biomineralization 2. Cite the reasons why poor calcium and vitamin D status may be increasing in prevalence. 3. Describe the factors that complicate laboratory ionized calcium is physiologically significant and tightly analysis of calcium and vitamin D status. regulated. In response to a decrease in ionized calcium, rapid release of parathyroid hormone (PTH) occurs, which Protect and Defend acts through several mechanisms in the kidneys and bones The adult human body contains nearly 1 kg of calcium, of to restore eucalcemia. In the distal nephron, PTH mediates which 99% is found in the hydroxyapatite salts of the continued on page 2 skeleton, endowing it with strength and stiffness.1 The cal- cium content of bone correlates directly with resistance to In This Issue fracture and can be clinically measured as the areal bone mineral density with dual-energy x-ray absorptiometry Calcium is the best-selling dietary supplement in the (DEXA). The presence of minor impurities makes skeletal United States, but achieving adequate intake of this salts soluble, an invaluable defense against hypocalcemia nutrient remains a challenge for many. This month’s during periods of low calcium intake. Consequently, when lead article reviews the importance of maintaining calcium consumption is insufficient, bone is preferentially proper calcium homeostasis through diet and not at the demineralized to meet systemic, calcium-dependent func- expense of skeletal calcium. Related articles will look tions (Table 1). Increased metabolic demands for calcium at the most recent clinical trials of calcium and vitamin are believed to explain, in part, the frequency of bone loss D supplementation, as well as a rare but potentially observed with aging and in various chronic inflammatory debilitating side effect of osteoporosis drug therapy. diseases. However, with sufficient intake of calcium and vitamin D and a functioning calcitropic hormonal axis, the Why Are We Calcium-Deficient? on A Paleolithic Perspective......................................4 04/08/2021 body can maintain the proper balance between the metabolic and structural needs for calcium. Supplementation and Bone Health: Calcium Homeostasis Interpreting the Latest Findings............................5 Of the three states of extracellular calcium—complexed What Does the WHI Study Tell Us (10%), protein-bound (40%), and ionized (50%)—only About Vitamin D Status? ......................................6 The author has disclosed that he has no significant relationships with or financial interests in any commercial organizations pertaining to this educational activity. Bone-Building Drugs Can Have Lippincott CME Institute, Inc., has identified and resolved all faculty conflicts Opposite Effect .....................................................7 of interest. The continuing education activity in Nutrition & the M.D.® is intended for physicians and health care professionals with an interest in nutrition-related disorders. 605899_NMD05_sw 5/25/06 2:19 PM Page 2 2 May 2006 Nutrition & the M.D. Editors Borrowing continued from page 1 Peter Pressman, MD, MS, FACN* Cedars-Sinai Medical Center, Los Angeles, CA Sunlight Roger Clemens, DrPH, CNS, FACN† University of Southern California, Los Angeles, CA UVB Editorial Administrative Support Debra K.W. Topham, MS, CNS OTC Knowledge Bank, Huntington Beach, CA Diet Vitamin D3 Vitamins Staff Writer Kevin Lomangino Vitamin D South Portland, ME 25-hydroxylase Editorial Board – Lilla Aftergood, PhD Liver University of California, Los Angeles, CA Judith Ashley, PhD, RD University of Nevada, Reno, NV 25(OH)D3 Brent A. Bauer, MD Mayo Clinic College of Medicine, Rochester, MN α P1 and other 25(OH)D-1 – Michael A. Bush, MD factors hydroxylase Cedars-Sinai Medical Center, Los Angeles, CA Dennis W. Cope, MD, FACP +/– Kidney University of California, Los Angeles, CA 1,25(OH )D 1,25(OH )D Ellen DiGiampaolo RD 2 3 2 3 Inglewood, CA David S. Gray MD – Sonoma Developmental Center, Eldridge, CA Clare M. Hasler, PhD, MBA PTH University of California, Davis, CA Penny M. Kris-Etherton, PhD, RD Bone PTH Penn State University, University Park, PA Denise B. Schwartz, MS, RD, FADFA, CNSD Intestine Providence St. Joseph Medical Center, Studio City, CA Linda Strause, PhD Parathyroid Strategic Research Management Consultant, Del Mar, CA glands Randy K. Ward, MD 2 2- 2 2- Medical College of Wisconsin, Milwaukee, WI Ca +HPO4 Ca +HPO4 *Dr. Pressman has disclosed that he is/was a member of the speakers bureau for Pfizer. Calcification Blood † Dr. Clemens has disclosed that he has no significant relationships with or financial inter- calcium ests in any commercial organizations pertaining to this educational activity. Nutrition & the MD® (ISSN 0732-0167) is published monthly Figure 1. The calcitropic hormonal axis. OTC, over-the- by Lippincott Williams & Wilkins, Inc., 16522 Hunters Green Park- way, Hagerstown, MD 21740-2116. Customer Service Manager, counter; PTH, parathyroid hormone; UVB, ultraviolet B. Audrey Dyson: Phone (800) 787-8981 or (410) 528-8572. 24-Hour Reprinted with permission from http://geneticslab. Fax (410) 528-4105 or Email [email protected]. Visit our website at LWW.com. Publisher, Daniel E. Schwartz: Phone (410) 528-4020, topcities.com/VitaminD%20homeostasis.jpg. Fax (410) 528-4105. Copyright © 2006 Lippincott Williams & Wilkins, Inc. All rights reserved. Periodicals avid reabsorption of filtered calcium, whereas in the proxi- Postage paid at Hagerstown, MD, and at additional mailing offices. POSTMASTER: Send address changes to Nutrition & the MD®, Subscription Dept., Lippincott Williams & mal tubule, it promotes generation of the active vitamin D Wilkins, P.O. 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All comments are for general guidance only; professional Despite the critical importance of calcium, humans are counsel should be sought for specific situations. ill-adapted to conserve dietary calcium, as illustrated by ©2006, Lippincott Williams & Wilkins, (800) 787-8981 605899_NMD05_sw 5/25/06 2:19 PM Page 3 Nutrition & the M.D. May 2006 3 the fact that the fractional intestinal absorption of to 1,25-dihydroxyvitamin D.6 Calcium requirements can calcium is only 10%, half of which is then excreted in be met through various foods (many of which do not the urine!2 This disregard for dietary calcium is a rem- contain lactose) and supplements and should always be nant of the environment in which