Preface to revised edition

Preface to revised edition

Preface to revised edition The fields of chromium, Cr, biochemistry, and nutrition have changed dramatically in the last 10 years since the first edit...

33KB Sizes 0 Downloads 242 Views

Preface to revised edition The fields of chromium, Cr, biochemistry, and nutrition have changed dramatically in the last 10 years since the first edition of this book appeared in 2007 and in directions that several of the authors predicted. The field of chromium has changed so much in the last decade that even researchers who work on the peripheries of the field are unaware of the changes. As coeditor of a journal focused on trace element research, I see manuscripts on Cr research every week that fail to reflect the current status of the field. Thus researchers in the field of nutrition and biochemistry may be shocked to see a summary of advances and state of the art in the field. Most significant will be a discussion of why after 50 years of being considered an essential trace element that chromium has been removed from the list of essential elements; no element has ever been removed from the list before, the list has only grow over the decades. Millions of people consume chromium nutritional supplements unaware that the data demonstrating beneficial effects has been effectively refuted over the last decade. That the lack of clinical effects of chromium(III) supplementation on effects of diabetes may result from humans receiving proportionally smaller doses than rodents (where supplementation has beneficial effects on insulin sensitivity and cholesterol levels) could hopefully spur clinical trials using larger doses of chromium. More specifically, when the first edition was written, Cr was considered an essential trace element for mammals and humans, but the European Food Safety Authority has determined that this is not the case. The effects of Cr at the time were generally held to be nutritionally, and not pharmacologically, relevant. The field has entirely reversed, based largely on research by the editor. The effects of chromium are now considered pharmacologically relevant, not nutritionally relevant. Yet, these effects have only clearly been established in rodent and rodent models of disease, not in humans. Ten years ago, the levels of Cr in the body were generally considered in the field to be controlled by urinary loss; this is now believed to be controlled by intake, another complete reversal driven largely by the editor’s research. Health concerns existed that Cr(III) was toxic at nutritional doses 10 years ago; now no upper tolerable limit exists for chromium and suggestions have been made that doses used in Cr supplementation could be safely increased an order of magnitude. However, potential toxic effects would need to be monitored closely at any increased dose. Chromium(III) addition to total parenteral nutrition (TPN) was deemed essential 10 years ago; now calls are appearing for the removal of chromium from TPN. At the time of the last book, the sales of products containing Cr picolinate, the most popular Cr supplement, were around ½ billion dollars annually. Since that time, the major supplier of Cr picolinate has gone bankrupt. At the time of the first edition, Cr had been approved in the United States as a supplement for feed for pigs; now this has been expanded to cattle and chickens. In short, the general perception of the field covered by this book has been flipped on its head in the last decade, and a reappraisal is in desperate need. The original aim of this book was to examine the four most controversial areas of chromium nutrition and chemistry: is chromium an essential element; what

xv

xvi

Preface to revised edition

biochemical role if any does chromium(III) have in the body; can large doses of chromium(III) be used to treat type II diabetes, cardiovascular disease, and related medical conditions; and is the use of chromium(III) supplements a health concern. This is continued in the revised edition. This is accomplished by having chapters in these four areas written by multiple experts. A decade ago the goal was to have the experts generally voice opinions on both sides of the issue. Ten years later, this is not as simple. For example, currently data are generally believed to be lacking in support of Cr being an essential element. Other areas lack such clarity. Discrepancies in the effects of Cr on rodent and rodent models of disease and on human subjects still lack firm resolution, while hypotheses for the molecular mechanism of chromium action continue to appear, even though all lack sufficient evidence from in vivo studies to confirm or often disprove them. Calls for clinical trials using larger doses of Cr are appearing; however, these trials would require careful monitoring for toxic effects. In Chapter 1, I and my graduate student Silas Brown (Department of Chemistry, The University of Alabama) outline the research on Cr from the time it was first proposed to be an essential element until 2007, just over a decade ago when the first edition of this book appeared. Two chapters address the first aim of the book— whether Cr is an essential element or has any effects as a nutritional supplement. In Chapter  2, Dr. Henry Lukaski (Department of Kinesiology and Public Health Education, University of North Dakota and formerly Assistant Director of the Grand Forks Human Nutrition Center of the USDA) reviews evidence for effects from Cr supplementation on changes in body mass and body composition and other parameters, while in turn, Dr. Merlin Lindemann (Department of Animal and Food Sciences, University of Kentucky) describes the effects of Cr supplementation of animal feed in Chapter 3. Two chapters address the second aim—whether chromium has a biochemical role in the body. In Chapter 4, I and my graduate student Kyle C. Edwards (Department of Chemistry, The University of Alabama) review how Cr is transported in the body and what this might imply about potential functions for chromium. In Chapter  5, Dr. Sreejayan Nair (School of Pharmacy, University of Wyoming) reviews the recent proposals for how Cr might affect carbohydrate and lipid metabolism. Aim 3 is addressed in three chapters. The effects of Cr supplementation of rodents and rodent model of disease are discussed by Dr. Zbigniew Krejpcio (Department of Human Nutrition and Hygiene, Poznan University of Life Sciences) in Chapter 6. Chapter 7 by Dr. Rebecca B. Costello, Dr. Johanna T. Dwyer, and Dr. Joyce M. Merkel (Office of Dietary Supplements, National Institutes of Health) reviews the potential use of Cr as a therapeutic agent. Dr. Debasis Bagchi (Departments of Pharmaceutical and Pharmacological Sciences, University of Houston) and colleagues in Chapter 8 provide an examination of the potential effects of chromium supplementation and interestingly contrasting opinions from authors of several other chapters. Chapters  9–11 comprise aim 4 and are, thus, focused on whether chromium supplementation could result in any toxic effects, perhaps still the hottest and most highly debated area of current chromium research. Dr. Peter Lay and Dr. Aviva Levina (School of Chemistry, University of Sydney) in Chapter 9 discuss the i­mplications

Preface to revised edition

of recent studies that indicate that Cr(III) complexes may be redox active in vivo. In Chapter 10, Dr. Xianglin Shi and coworkers (Center for Research on Environmental Disease, University of Kentucky) look at a specific area of potential Cr(III) toxicity, oxidative stress. Dr. Max Costa and Anthony Murphy (Department of Environmental Medicine, New York University School of Medicine) in Chapter 11 survey toxicological studies on Cr(III) compounds. Finally, Dr. Forrest Nielsen, a distinguished nutritionist at the Grand Forks Human Nutrition Center of the USDA but who has not worked directly in the field of Cr nutritional biochemistry, has returned in the revised edition to provide a summary of the arguments in each of the four areas and presented his own conclusions and interpretations in the concluding chapter (Chapter 12). John B. Vincent Department of Chemistry, The University of Alabama, Tuscaloosa, AL, United States

xvii