Statistical validation and application of the waist-height ratio in children and adolescents.

Smita Nambiar (2011). Statistical validation and application of the waist-height ratio in children and adolescents. PhD Thesis, School of Medicine, The University of Queensland.

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Author Smita Nambiar
Thesis Title Statistical validation and application of the waist-height ratio in children and adolescents.
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2011-07
Thesis type PhD Thesis
Supervisor Professor Peter SW Davies
Professor Helen Truby
Total pages 232
Total colour pages 1
Total black and white pages 175
Subjects 11 Medical and Health Sciences
Abstract/Summary ABSTRACT Introduction The waist-height ratio (WHtR) is a relatively new anthropometric index that identifies individuals with greater abdominal adiposity who are at higher risk of developing cardiovascular disease and type 2 diabetes. A WHtR cut-off of ≥0.5 marks an increased risk of obesity related co-morbidities among adults. Research into the use of the WHtR in children is of growing importance but remains to be validated in this population group. This thesis has six objectives: 1. To statistically validate the WHtR for use in children and adolescents 2. To develop age and sex appropriate cut-offs to define high and very high abdominal adiposity 3. To explore the association between the WHtR and the duration of predominant breastfeeding 4. To explore the association between the WHtR and the consumption of ‘non-core’ foods. 5. To assess the utility of the waist-height ratio as an tool to measure parental perception of their child’s weight, and finally 6. To assess the usefulness of the WHtR in the clinical setting by testing whether the WHtR could be used to predict the presence of the metabolic syndrome in obese adolescents. For each objective, BMI definitions for at-risk of overweight and obesity were included in analyses for comparative purposes. Methodology Data generated from the following studies was utilised: • The Australian Health and Fitness Survey (AHFS) 1985: 8484 subjects aged 8.00-16.00 years • The Healthy Kids Queensland (HKQ) Physical Activity and Nutrition Survey 2006: 3691 subjects drawn from school years 1, 5 and 10 • The ‘Eat Smart’ study- 2007-09: 111 subjects aged 10.00-17.99 years Objective 1: Height, weight, and WC data from HKQ were used to statistically validate the WHtR using log-log regression analyses. Objective 2: Height, weight, WC and skinfolds data from AHFS were used to develop age and sex appropriate cut-offs using two different methods- 1.Receiver Operating Characteristic (ROC) curves selected a cut-off value that was most sensitive and specific in identifying children ≥85th and ≥95th percentiles for percentage body fat (%BF); 2.Cut-offs were derived using the LMS method (a statistical method used to obtain normalized centile standards for any anthropometric measurement). Objectives 3-5: Anthropometric data, information on early feeding behaviour, a 24-hour food and drink record and information related to overweight perception from HKQ were collected to explore the association between abdominal adiposity and duration of predominant breastfeeding; the consumption of ‘non-core’ foods and the perception of body weight, respectively. Objective 6: Biochemical (blood lipids, blood glucose and insulin), blood pressure and anthropometric data from ‘Eat Smart’ were used to explore the ability of the WHtR to predict the presence of the metabolic syndrome in obesity. Results Objective 1: Results indicated that the WHtR was only statistically valid for use among Year 1 subjects and Year 10 females. Biologically however, the r2 values obtained from the correlation between WHtR and height were extremely weak for all ages and both sexes, suggesting that it is biologically plausible to use this index in children and adolescents aged 5-17 years. Objective 2: A cut-off of 0.45 and 0.47 for females and 0.46 and 0.48 for males corresponded to the 85th and 95th percentile for %BF respectively. For the WHtR cut-offs determined using the LMS method, the 85th percentile was 0.48 and 0.49 respectively for females and males, while the value of 0.52 marked the 95th percentile for both sexes. The WHtR cut-off values based on %BF were significantly more sensitive than the current BMI cut-offs for obesity in identifying children with the highest percentage of body fat. Objective 3: Year 1 females who were breastfed as infants had smaller mean WHtR than those were never breastfed. Females who were breastfed for at least 4-6 months had the lowest mean WHtR. Later introduction of solids was associated with lower mean WHtR among males only. Objective 4: The consumption of non-core foods were weakly, but significantly associated with very high abdominal obesity in males and females from Years 5 and 10. Approximately 40% of the study samples’ energy intake came from non-core foods and beverages. Children were consuming more than double the number of recommended serves of non-core foods and drinks. Objective 5: The sensitivity of parents’ ability to identify obese children in Year 5 was slightly higher when the LMS WHtR cut-off (95th percentile) was used, suggesting that parental perception of obesity status was related more closely to a visual measure of overweight such as the WHtR compared to BMI. Objective 6: The WHtR proved to be a significant predictor of the metabolic syndrome in obese adolescents of which 1 in 5 had features of the metabolic syndrome. Conclusion The WHtR has been statistically validated for use in children and adolescents. The most noteworthy findings in this Thesis were that WHtR cut-offs based on %BF were significantly more sensitive than the current BMI obesity cut-offs in identifying children with the highest percentage of body fat; and WHtR was the most significant predictor of the metabolic syndrome in obese children. This warrants the acceptance of the WHtR as a non-invasive screening method to identify the child with the body shape most associated with cardiovascular health risks and diabetes. This Thesis demonstrates that the WHtR has a very significant place in both population health research and clinical practice. Key Words: Waist-height ratio, children, adolescents, obesity, abdominal adiposity, cardiovascular risk factors Australia New Zealand Standard Research Classifications (ANZSRC) 111403 Paediatrics 60% 111706 Epidemiology 20% 111199 Nutrition and Dietetics not elsewhere classified 20%
Keyword Waist-height ratio
Children & Adolescents
abdominal adiposity
cardiovascular risk factors
Additional Notes Figure 1.0 on page 24 should be printed in colour 175 pages are in pure black and white. Please note that 56 pages in the document contain 1 figure and tables that have very light grey shading so it is easier to read. Therefore grey scale printing would be the best option. These pages are: 25, 30 (figure 1.2) 59, 60, 62, 64, 76, 77, 78, 79, 84, 85, 86, 96, 101, 102, 103, 104, 105, 106, 115, 116, 120, 121, 122, 123, 124, 132, 133, 134, 135, 136, 137, 138, 147, 148, 149, 151, 152, 153, 155, 169, 172, 173, 174, 175, 176, 185, 186, 187, 188, 194, 195, 196, 197 and 198 Lanscape pages (total 24 pages): 33, 84, 101, 102, 103, 104, 105, 106, 132, 133, 134, 135, 136, 137, 138, 151, 152, 153, 154, 155, 185, 186, 187, 188

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Created: Mon, 25 Jul 2011, 15:52:15 EST by Ms Smita Nambiar on behalf of Library - Information Access Service