Читать книгу Vitamin D in Clinical Medicine - Группа авторов - Страница 7
ОглавлениеVitamin D: A Key Player in Clinical Medicine
The essential role of vitamin D in bone health has been known for more than a century [1]. The early appreciation of vitamin D as a key skeletal element has been augmented more recently by apparent extra-skeletal effects of vitamin D. The notion that vitamin D is a multifunctional hormone intersecting across many organ systems has raised enormous interest in the scientific community and among the general population [2]. Not unexpectedly, as a consequence, the commercial market for vitamin D has expanded significantly with its use being touted as a preventive and therapeutic measure for many human diseases. This book tackles some of the most important issues that have emerged from this fast-moving area of clinical medicine.
Several chapters of the book focus on the assays of vitamin D and its binding protein. The diagnosis of hypovitaminosis D is based on measuring 25-hydroxyvitamin D [3]. Unfortunately, the assays lack international standardization and suffer from the use of heterogeneous methods in clinical practice [3–5]. Reliability of the assays is crucial, since different laboratory cutoff values may be used to define hypovitaminosis D [5]. To a certain extent, the epidemiology of vitamin D deficiency in the population is also dependent upon the age of the population being studied. Aging skin becomes a less efficient source of vitamin D because the enzymatic system involved in the conversion steps from 7-dehydocholesterol is impaired [6].
A key nonskeletal action of vitamin D is that which is related to muscle metabolism and, thus, a chapter of the book is dedicated to how aging affects an associated complication, namely, sarcopenia and, in turn, how sarcopenia is affected by vitamin D deficiency.
Several chapters are devoted to primary or secondary states of altered PTH secretion and during glucocorticoid treatment [7].
Hypovitaminosis D today is frequent not only among the elderly but also among children. This is due, in part, to systemic diseases, to changes in lifestyle, such as children not being sufficiently exposed to sunlight or being in an environment that limits sun exposure because of air pollution, as well as to the wider use of sunscreen lotions [8]. The diet does not compensate for the inconstant source of vitamin D from the sun because vitamin D is found naturally in relatively few foods and in many countries there is no fortification of food with vitamin D [9]. These issues are covered in 2 chapters of the book which deal with vitamin D in children and their nutritional requirements for vitamin D.
Many observational and some interventional studies have linked vitamin D to cardiovascular disease, cancer, and diabetes. In addition, reduced levels of vitamin D have been associated with increased mortality [10]. One chapter critically analyzes the evidence for these potential extra-skeletal actions of the hormone. Another chapter is devoted exclusively to vitamin D and diabetes mellitus.
Finally, many uncertainties exist on the management of hypovitaminosis D. Most guidelines recommend the use of cholecalciferol, but other forms of vitamin D may be used in selected clinical conditions. Replacement regimens have also become controversial, particularly in the context of severe hypovitaminosis [11]. Replacement regimens elicit discussion about monitoring and goals of therapy. Therefore, one of the chapters deals with these practical issues.
We hope that this book will offer new insights in a balanced way about these important issues related to vitamin D in the clinical arena.
Andrea Giustina , Milan
John P. Bilezikian, New York, NY
References
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