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      Thyroid Hormones and Their Relation to Weight Status

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          Abstract

          Background/Aims: The aim of this study was to analyze thyroid hormones in female adolescents with obesity and anorexia nervosa (AN) before and after normalization of weight. Methods: Thyroid-stimulating hormone (TSH), fT3, and fT4 were determined in 100 obese girls, 32 normal-weight girls and 20 girls with AN aged 14–18 years at baseline and 1 year later. Additionally, leptin, insulin, and the insulin resistance index HOMA were analyzed in the obese and normal-weight girls. Results: TSH and fT3 levels of girls with AN were significantly lower compared to TSH concentrations of normal-weight girls, while TSH and fT3 levels of the obese girls were significantly higher. The 21 obese females with weight loss >5% demonstrated a significant decrease in fT3 and TSH, while the 9 adolescents with AN and weight gain >5% showed a significant increase in fT3 and TSH. Insulin and HOMA were not significantly correlated to TSH, fT3 and fT4, while leptin was correlated to TSH and fT3 in both cross-sectional and longitudinal analysis. Conclusions: Thyroid function seems to be reversibly related to weight status with increased TSH and fT3 concentrations in obesity and decreased TSH and fT3 levels in AN. We hypothesize that leptin may be the link between weight status and TSH.

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          Most cited references 21

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          The assessment of insulin resistance in man.

          Insulin resistance exists when a normal concentration of insulin produces a less than normal biological response. The ability to measure insulin resistance is important in order to understand the aetiopathology of Type 2 diabetes, to examine the epidemiology and to assess the effects of intervention. We assess and compare methods of measurement and have undertaken a literature review from 1966 to 2001. Quantitative estimates of insulin resistance can be obtained using model assessments, clamps or insulin infusion sensitivity tests. There is considerable variation in the complexity and labour intensity of the various methods. The most well-established methods are the euglycaemic clamp, minimal model assessment and homeostatic model assessment (HOMA). No single test is appropriate under all circumstances. There are a number of well-established tests used to measure insulin resistance: the choice of method depends on the size and type of study to be undertaken. Although the so-called 'gold-standard' test, the euglycaemic clamp, is useful for intensive physiological studies on small numbers of subjects, a simpler tool such as HOMA is more appropriate for large epidemiological studies. It is important to be aware that most techniques measure stimulated insulin resistance whereas HOMA gives an estimate of basal insulin resistance. Caution should be exercised when making comparisons between studies due to variations in infusion protocols, sampling procedures and hormone assays used in different studies.
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            Hyperthyrotropinemia in obese children is reversible after weight loss and is not related to lipids.

            There is some controversy whether T(4) treatment is indicated in obese humans with hyperthyrotropinemia. The objective of this study was to examine whether hyperthyrotropinemia is a cause or a consequence of obesity. The study was designed as a cross-sectional comparison between obese and lean children and includes a 1-yr follow-up study. The study was set in a primary care facility. The patients were 246 obese and 71 lean children. The 1-yr intervention program was based on exercise, behavior therapy, and nutrition education. The main outcome measures were TSH, free T(3) (fT3), free T(4) (fT4), high-density lipoprotein, low-density lipoprotein, and total cholesterol at baseline and 1 yr later. TSH (P = 0.009) and fT3 (P = 0.003) concentrations were significantly higher in obese children than in normal weight children, whereas there was no difference in fT4 levels (P = 0.804). Lipids did not correlate significantly to thyroid hormones in cross-sectional and longitudinal analyses. fT3, fT4, and lipids did not differ significantly in the 43 (17%) children with TSH levels above the normal range from the children with TSH levels within the normal range. Substantial weight loss in 49 obese children led to a significant reduction of TSH (P = 0.035) and fT3 (P = 0.036). The 197 obese children without substantial weight loss demonstrated no significant changes of thyroid hormones. Because fT3 and TSH were moderately increased in obese children and weight loss led to a reduction, the elevation of these hormones seems to be rather a consequence of obesity than a cause of obesity. Because fT3 and TSH were both increased in obesity and thyroid hormones were not associated to lipids, we put forward the hypothesis that there is no necessity for thyroxine treatment.
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              Serum TSH is positively associated with BMI.

              To investigate whether there is an association between serum thyroid-stimulating hormone (TSH) within the normal range and body mass index (BMI). The study was performed in 6164 subjects (2813 males) who attended the fifth Tromsø study in 2001, and in 1867 subjects (873 males) that attended both the fourth Tromsø study in 1994/1995 as well as the fifth Tromsø study. Height, weight, and serum TSH were measured in all subjects, and smoking status was recorded. Smokers and nonsmokers were analyzed separately. In the fifth Tromsø study, serum TSH was positively and significantly associated with BMI in the nonsmokers. Within the normal TSH range (defined as the 2.5-97.5 percentile), nonsmoking males in the highest TSH quartile had a mean BMI 0.4 kg/m(2) higher compared to those in the lower quartile, whereas the difference for nonsmoking women was 1.4 kg/m(2). Similarly, in nonsmokers in the longitudinal study, there was a significant and positive association between delta serum TSH (serum TSH in 2001 minus serum TSH in 1994) and delta BMI in those with serum TSH within the normal range both in 1994 and 2001. In these subjects, the quartile with the highest delta serum TSH had a mean increase in BMI from 1994 to 2001 that was 0.3 kg/m(2) higher compared to those in the quartile with the lowest delta serum TSH. For the smokers, relations between serum TSH and BMI were not statistically significant. In nonsmokers there is a positive association between serum TSH within the normal range and BMI.
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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                1663-2818
                1663-2826
                2008
                July 2008
                21 May 2008
                : 70
                : 1
                : 51-57
                Affiliations
                Departments of aPediatric Endocrinology, and bChild and Adolescent Psychiatry, Vestische Hospital for Children and Adolescents, University of Witten/Herdecke, Datteln, Germany
                Article
                129678 Horm Res 2008;70:51–57
                10.1159/000129678
                18493150
                © 2008 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 2, Tables: 1, References: 41, Pages: 7
                Categories
                Original Paper

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