Nutrient Regulation during Pregnancy, Lactation, and Infant Growth PDF
Preview Nutrient Regulation during Pregnancy, Lactation, and Infant Growth
NUTRIENT REGULATION DURING PREGNANCY, LACTATION, AND INFANT GROWTH ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY Editorial Board: NATHAN BACK, Stale University of New York at Buffalo IRUN R. COHEN, The Weizmann Institute of Science DAVID KRITCHEVSKY, Wistar Institute ABEL LAJTHA, N. S. Kline Institute for Psychiatric Research RODOLFO PAOLETTI, University of Milan Recent Volumes in this Series Volume 344 MECHANISMS OF PLATELET ACTIVATION AND CONTROL Edited by Kalwant S. Authi, Steve P. Watson, and Vijay V. Kakkar Volume 345 OXYGEN TRANSPORT TO TISSUE XV Edited by Peter Vaupel, Rolf Zander, and Duane F. Bruley Volume 346 INTERACTIVE PHENOMENA IN THE CARDIAC SYSTEM Edited by Samuel Sideman and Rafael Beyar Volume 347 IMMUNOBIOLOGY OF PROTEINS AND PEPTIDES VII: Unwanted Immune Responses Edited by M. Zouhair Atassi Volume 348 ADVANCES IN NUTRITION AND CANCER Edited by Vincenzo Zappia, Marco Salvatore, and Fulvio Della Ragione Volume 349 ANTIMICROBIAL SUSCEPTIBILITY TESTING: Critical Issues for the 90s Edited by James A. Poupard, Lori R. Walsh, and Bruce Kleger Volume 350 LACRIMAL GLAND, TEAR FILM, AND DRY EYE SYNDROMES: Basic Science and Clinical Relevance Edited by David A. Sullivan Volume 351 THE CHEMOKINES: Biology of the Inflammatory Peptide Supergene Family II Edited by I. J. D. Lindley, J. Westwick, and S. Kunkel Volume 352 NUTRIENT REGULATION DURING PREGNANCY, LACTATION, AND INFANT GROWTH Edited by Lindsay Allen, Janet King, and Bo Lonnerdal A Continuation Order Plan is available for this series. A continuation order will bring deli very of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher. NUTRIENT REGULATION DURING PREGNANCY, LACTATION, AND INFANT GROWTH Edited by Lindsay Allen University of California-Davis Davis, California Janet King University of California-Berkeley Berkeley, California and Bo Lonnerdal University of California-Davis Davis, California SPRINGER SCIENCE+BUSINESS MEDIA, LLC Library of Congress Catalog1ng-1n-Publication Data Nutrient regulation during pregnancy, lactation, and infant growth / edited by Lindsay Allen, Janet King, and Bo Lo'nnerdal. p. cm. — (Advances in experimental medicine and biology ; v. 352) "Proceedings of a conference on nutrient regulation during pregnancy, lactation, and infant growth, held August 9-12, 1992, in Stockholm, Sweden, and in Helsinki, Fin1 and"--T.p. verso. Includes bibliographical references and index. 1. Metabolism in pregnancy—Congresses. 2. Pregnancy—Nutritional aspects—Congresses. 3. Lactation—Nutritional aspects—Congresses. 4. Fetus—Metabolism—Congresses. 5. Fetus—Nutrition—Congresses. 6. Infants—Metabolism—Congresses. I. Allen, Lindsay, 1946- II. King, Janet, 1941- . III. LÖnnerdal, Bo, 1948- IV. Series. [DNLM: 1. Nutrition—congresses. 2. Pregnancy—metabolism- -congresses. 3. Lactation—metabolism—congresses. 4. Growth- -congresses. W1 AD559 v.352 1994 / QU 145 N9702 1994] RG559.N83 1994 618.2'4—dc20 DNLM/DLC for Library of Congress 94-6848 CIP Proceedings of a conference on Nutrient Regulation during Pregnancy, Lactation, and Infant Growth, held August 9-12, 1992, in Stockholm, Sweden, and in Helsinki, Finland ISBN 978-1-4899-2577-0 ISBN 978-1-4899-2575-6 (eBook) DOI 10.1007/978-1-4899-2575-6 © Springer Science+Business Media New York 1994 Originally published by Plenum Press, New York in 1994 Softcover reprint of the hardcover 1st edition 1994 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher PREFACE Almost every aspect of energy and nutrient metabolism is altered by hormonal and other physiological changes during pregnancy and lactation. While it is evident that hormonal adjustments affect nutrient requirements, these are rarely considered when nutrient recommen dations are made for pregnant or lactating women, and often neglected during evaluation of nutritional status. In addition, changes in nutrient metabolism during the stages of pregnancy and oflactation are usually considered separately, while in reality events during pregnancy can have a major influence on nutritional status and nutrient requirements during lactation. The purpose of this volume is to describe changes in the metabolism of important nutrients during pregnancy and lactation, including the physiological basis for these changes and their implications for nutrient requirements and assessment. Authors have considered such issues as inter-relationships between endocrine changes and nutrient metabolism at the tissue, cellular and molecular level; alterations in nutrient binding proteins; the efficiency of nutrient absorp tion and retention; and the impact on maternal as well as fetal nutritional status. Another unique aspect of this book is the focus on pregnancy and lactation as a continuum. While it is evident that nutrient metabolism and balance during pregnancy may affect nutrient homeostasis and requirements during lactation, investigators have paid little attention to this issue. It is our hope that the information presented here will encourage the design of future studies that continue throughout pregnancy and lactation. For some nutrients, such as energy and calcium, the continuum may need to extend to the post-lactation period. The first section of this book discusses energy balance and body composition changes in pregnancy and lactation. Surprisingly little is known about the regulation of energy balance and maternal tissue composition during this period. There is a very wide range of pregnancy weight gain among healthy women, the causes and consequences of which are poorly understood. However, relatively recent analyses of national survey data in the United States show that maternal size is inversely related to pregnancy gain, to the extent that newer recommendations for weight gain are based on maternal body mass index (BMI). These observations suggest that energy balance in pregnancy involves physiological processes that are affected by maternal body composition. Pregnancy weight gain and energy balance will also affect the amount of fat retained postpartum, which may then affect lactation performance and maternal energy intake during lactation. The nature of these processes and their regulation are explored in Chapters 1 to 8. Pedro Rosso and Sofia Salas focus on how maternal body mass can affect maternal-fetal transfer of nutrients, in both animal and human models. They conclude that the lower plasma volume of underweight women reduces placental blood flow and nutrient transfer to the fetus. The smaller feto-placental unit is associated with lower production of steroid hormones which in turn may reduce the secretion of hormones in the renin-angiotensin-aldosterone system and other vasoactive substances. v vi Preface Andrew Prentice and his colleagues review energy balance during pregnancy and lacta tion, including relatively new data obtained by using whole-body calorimetry and doubly-la belled water techniques. These techniques now allow us to estimate each of the components of energy expenditure. It has become apparent that women's prepregnancy body fat is directly related to their increase·in basal metabolic rate during pregnancy, and that the low BMR increment of pregnant underweight women may be an appropriate adaptive response to maintain energy balance under energy-limited conditions. Such adaptation does not occur in lactation, where energy requirements are met by increased food intake, a reduction iri physical activity and, when necessary, mobilization of maternal fat. The authors show that changes in physical activity have a major influence on energy requirements during pregnancy and lactation and propose that there is a tendency to underestimate the energy intake of pregnant women. Body composition also affects energy intake, as discussed by J.-P. Flatt. A model is described to explain how the macronutrient composition of the diet interacts with exercise to affect energy balance and body weight. In addition, he speculates that changes in maternal fat stores during pregnancy and lactation are probably influenced by the ratio of fat to carbohydrate in the diet. Mobilization of maternal stored energy is important for meeting the demands of fetal growth and both fetal and maternal metabolism during pregnancy, as well as milk production during lactation. For ethical and practical considerations it is difficult to study many aspects of metabolism-such as lipolysis-during pregnancy and lactation, and much more work has been performed in animal species. Dermot Williamson and Patricia Lund provide an extensive review of the regulation of lipid deposition and mobilization in the non-pregnant state, as well as the multiple cellular mechanisms that control changes in lipid metabolism in pregnant and lactating rat models. Alan Bell and Dale Bauman describe the value of domestic ruminants as a model for in vivo research on metabolic adaptations during pregnancy and lactation. They present information on how various tissues, including adipose, respond to regulatory hormones in these physiological states, and how these responses are coordinated through homeorhetic regulation. Margaret Neville and her coworkers have studied maternal glucose metabolism in human lactation. Using the euglycemic glucose-insulin clamp technique combined with measures of labelled glucose turnover in lactating women, they conclude that, in contrast to the situation during pregnancy, neither basal nor insulin-stimulated glucose disposal is affected by lactation. Rather, glucose transport activity of the mammary gland is particularly high in lactating women and is insensitive to insulin. Thus the situation in women seems to be different from that in many species in which decreased insulin sensitivity of peripheral tissues augments glucose flux to the mammary gland. The fmal chapters in this section of the book deal with the practical importance of maternal body composition in determining pregnancy outcome in Mexico, and lactation performance in Guatemala. Martinez et al. followed rural Mexican women throughout pregnancy and lactation. In spite of low pregnancy weight gains they observed the same inverse relationship between maternal fatness in early pregnancy and pregnancy weight gain that occurs in well-nourished women. Thinner women consumed more energy and deposited more weight and fat in pregnancy. In lactation they ate less energy, lost more weight and mobilized more fat compared to women who were fatter at conception. This study confirms the importance of adequate maternal body mass at conception and shows that pregnancy weight gain, energy intake or skinfold thickness changes may be poor indicators of maternal nutritional status in developing countries. Gonzruez-Cosslo et al. evaluated whether anthropometric measures of Guatemalan women in early lactation could predict the benefits of dietary supplementation on milk output and weight gain. Within a group of malnourished women, only those with lower fat or muscle Preface vii mass produced more milk when supplemented. This information can help to target nutrient intervention programs during lactation. The second section of the book, Chapters 9 to 14, is focussed on the transport of specific nutrients during pregnancy and lactation and how a better understanding of the underlying mechanisms may help in the diagnosis and treatment of nutritional deficiencies. To illustrate this area, a few select nutrients (iron, folate and vitamin Bn) were chosen, partly because of recently gained insights into these mechanisms, partly because of the well-recognized problem of widespread nutritional anemia world-wide. Surface-bound transferrin receptors are key regulators for the uptake of iron by various cell types. It has been found recently that a small fraction of these receptors circulate in the plasma in a slightly modified form. James Cook and his co-workers describe this receptor, its structure and characteristics and the regulation of its expression at a molecular level. They also review the normative data available in healthy individuals as well as describe the impact of altered erythropoiesis, iron status and physiological states such as pregnancy on these levels. They propose that elevated levels of the circulating transferrin receptor can be used as a sensitive indicator of tissue iron need. There is considerable concern that iron deficiency and anemia can adversely affect pregnancy outcome. In a chapter by Fernando Viteri, the nature of this problem is presented and ways to estimate physiological requirements of iron during pregnancy are reviewed. The consequences of iron deficiency anemia may involve both the pregnant woman and her fetus and some of the studies that have focussed on the maternal-fetal axis are discussed. An important factor that needs to be considered in all such studies is the physiological adaptation that occurs to compensate for the nutritional deficiency. This includes changes in blood volume and flow, intestinal absorption and placental size and function, which also are discussed in this chapter. The uptake and transport of folate by cells appear to be dependent on a family of folate-binding proteins. Jacob Selhub describes these proteins and the mechanisms of folate processing by various cells, with special emphasis on the placenta and the small intestine. The regulation of these mechanisms is discussed and special consideration is given to the uptake of folate by the mammary gland and its export into milk. The efficiency of various treatment regimes for combatting nutritional anemia is presented by Ousa Thanangkul. Using Thailand as an example, she describes field trials in which different forms of administering iron and folate have been used. By choosing optimal treatments, the incidence of iron deficiency anemia in pregnant Thai women could be reduced substantially. The present recommendations for folate intake during pregnancy and lactation as well as the studies on which they are founded are introduced in a chapter by Deborah O'Connor. This chapter also includes a detailed description of various indicators of folate status and their validity. In addition, the physiological changes affecting folate status during pregnancy and lactation are presented as well as the impact of folate status on maternal and fetal outcome. These are important considerations when determining strategies for folate supplementation. Deficiency of vitamin B12 can also lead to nutritional anemia, and the prevalence of this deficiency may have been underestimated. In a chapter by Lindsay Allen, the metabolism of vitamin B12 during pregnancy, lactation and infancy is described both at a cellular level and in physiological context. The proteins transporting vitamin B12 and its analogues between different body compartments are presented with special emphasis on the intestine, the placenta and milk. The requirements of vitamin B12 are discussed as is the occurrence of vitamin B12 deficiency in developing countries and its potential causes. The pregnant woman's current B12 intake may be an important determinant of fetal storage of the vitamin and its secretion in milk. The third section of this book, Chapters 15 to 23, focuses on the role of nutrients as regulators of growth in utero and postnatally. Inadequate intakes of energy, protein, or of viii Preface specific nutrients limit growth in experimental animals and in humans. But, the underlying causes of these defects in growth are not well understood. The roles of vitamin A, zinc, vitamin D and calcium in growth and development are explored in this section. The biochemical basis as well as the clinical evidence for the importance of these nutrients in prenatal and postnatal growth are discussed in the chapters. The first two chapters focus on vitamin A and growth. Catharine Ross and Elizabeth M. Gardner review the molecular mechanism whereby vitamin A affects differentiation, especially during embryonic development. They provide data to show that placental transport of vitamin A during pregnancy is tightly regulated. The situation is quite different during lactation, however. Circulating chylomicrons are the source of vitamin A for the mammary gland, and because the amount of vitamin A in utero is related to maternal vitamin A intake, the concentration of vitamin A in milk is directly linked to maternal vitamin A status. In the following chapter Barbara Underwood examines the role for vitamin A in postnatal growth and survival. A meta-analysis of severt different studies shows that vitamin A deficiency does not limit growth among infants and children in developing countries possibly because other nutrients are more limiting in the diet. Supplementation with vitamin A, however, does reduce the risk of death from disease by 20-30%. Since vitamin A is readily transferred in breast milk, the vitamin A status of infants could be improved by giving malnourished mothers a direct dose of vitamin A (possibly 300,000 IU) within four weeks of delivery. The role of zinc in growth and development is examined in the next three chapters. Zinc is essential for normal growth and development both in utero and after birth. George Bunce and his colleagues provide extensive data showing that an intake of zinc is also crucial for normal parturition. Zinc deficient animals have delayed, prolonged and difficult labors due to an inability to synthesize proteins required for parturition in a timely manner. In the following chapter, Henri Dirren and his coworkers summarize the results of their study of zinc and growth in children between 12-50 months of age in Ecuador. After zinc supplementation for a 15 month period, a significant increase in height was seen both boys and girls, but the supple mented boys grew more (1.0 cm) than the girls (0.6 cm). This is the first evidence that zinc deficiency limits growth in rural Ecuadorian children. Given the essential need for zinc to support growth and development, Nancy Krebs and her colleagues examine the capacity of infants to maintain zinc homeostasis over a wide range of zinc intakes in the following chapter. Using a stable isotope technique, they conclude that breast-fed infants maintain zinc homeo stasis by both a high fractional absorption and a low endogenous excretion. Formula-fed infants, who receive higher zinc intakes than breast-fed infants, have lower rates of absorption. Thus, newborn infants regulate zinc levels in response to variation in intake by modifying intestinal absorption or excretion. The next three chapters focus on the role of vitamin D and calcium in growth and differentiation. First, Bernard Halloran extensively reviews the molecular basis for a role of vitamin D in cellular differentiation across a variety of different species. Vitamin D is essential for normal growth and development postnatally, but its role in embryogenesis and fetal development remains unclear even though vitamin D and its metabolites are found in a number of fetal tissues. Because calcium intakes are limited in parts of the world, the influence of low calcium intakes on vitamin D metabolism is examined in the next chapter. David Fraser reviews data showing that vitamin D is enhanced in experimental animals fed low calcium diets. With calcium deficiency an increased secretion of parathyroid hormone stimulates the kidney to produce more 1,25(OHhD which in turn activates the metabolic degradation of 25(OH)D. There is evidence that this is also true for humans. Individuals who have limited intakes of dietary calcium and little exposure to sunlight are at risk for vitamin D deficiency. Although exposure to sunlight is adequate, intakes are very low in The Gambia (about 400 mg/d). Ann Prentice and her colleagues studied the impact of a low calcium intake on calcium homeostasis Preface ix during lactation in this population. In comparison to lactating women and their infants in England, women in The Gambia have a lower concentration of calcium in their breast milk and their infants show a progressive decline in bone mineral content during the fIrst 36 months of age. Bone mineralization may be limited in infants breast-fed by mothers consuming low calcium diets. The nutrients examined in these chapters showed that only zinc defIciency limits growth in both animals and humans. Marginal intakes of vitamin A do not limit growth but are associated with an increased risk of morbidity and mortality in infants and preschool children. A low intake of calcium during lactation leads to reduced bone in children. Biochemically, zinc, vitamin A and vitamin D may be linked. In the last chapter of this section, George Bunce reviews the role for "zinc fIngers," which are DNA binding domains stabilized by a zinc atom and found in receptors for vitamins A and D. He speculates that small defIcits in cellular zinc pools may impair the function of vitamins A and D. The fInal section of this book includes two chapters from a workshop on the use of stable isotopes to study regulation of nutrient utilization in pregnant and lactating women and neonates. Alfred Yergey reviews the theories of constant tracer infusion and applies those theories to some issues regarding mineral metabolism. David Hachey describes some of the principles of mass spectrometry and presents studies of fat metabolism during lactation using stabl~ isotope methodology.
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