Elsevier

Clinical Therapeutics

Volume 33, Issue 10, October 2011, Pages 1466-1474
Clinical Therapeutics

Pharmaceutical economics & health policy
Original research
Association Between Body Mass Index and Health-Related Quality of Life Among an Australian Sample

https://doi.org/10.1016/j.clinthera.2011.08.009Get rights and content

Abstract

Objective

This study investigated the association between body mass index (BMI) and changes in BMI over time with health-related quality-of-life data among a general and representative sample of the Australian population.

Methods

The sample consisted of respondents between the ages of 18 and 79 who completed the Household, Income and Labour Dynamics in Australia (HILDA) Survey in 2007 and 2009. These respondents completed the SF-36 questionnaire and provided data on their height, weight, medical conditions, and sociodemographic characteristics. SF-36 questionnaire responses were converted into health state utility values using the SF-6D algorithm. Regression analysis was used to examine the relationship between BMI and utility, controlling for a range of obesity-related medical conditions and sociodemographic characteristics.

Results

Obese men (BMI value ≥30) had, on average, a lower utility score (–0.0190, P < 0.001) than men within an “acceptable” BMI range (BMI 18.5 to <25). Obese women (BMI value ≥30) also had, on average, a lower utility score (–0.0338, P < 0.001) than women within an acceptable BMI range (18.5 to <25). Although BMI was not associated longitudinally with utility, there was a statistically significant negative longitudinal relationship between arthritis (–0.0153, P < 0.01) and depression/anxiety disorders (–0.0358, P < 0.001) and utility.

Conclusions

Cross-sectional results suggest that BMI is negatively associated with utility and that further investigation of the longitudinal relationship between BMI and utility is warranted.

Introduction

Obesity has become a worldwide epidemic. Based on measured height and weight data from the National Health and Nutrition Examination Survey, it is estimated that nearly one third of the US population is obese.1 In Australia, by way of comparison, it is estimated that one fourth of the population is obese based on measured height and weight data from the 2007–2008 National Health Survey.2 The degree to which a person is classified as being overweight is usually defined by body mass index (BMI), which is calculated as weight in kilograms divided by height in meters squared. The World Health Organization (WHO) defines an “acceptable” weight as a BMI value between 18.5 and <25, overweight as a BMI value between 25 and <30, and obese as a value ≥30.3

The medical literature has demonstrated clearly that being overweight or obese is a risk factor for many serious medical conditions, including type 2 diabetes, hypertension, coronary heart disease (CHD), elevated cholesterol levels, depression, musculoskeletal disorders, gallbladder disease, and several cancers.4, 5, 6 Moreover, evidence from the Framingham Heart Study has indicated this increased risk of diseases can also result in relatively large decrements in life expectancy.7 Although many of these medical conditions associated with obesity increase the risk of mortality, they also affect an individual's health-related quality of life (HRQoL).8, 9, 10, 11, 12, 13, 14

In measuring HRQoL, health outcome researchers have generally used utility-based methods to obtain individual preferences through techniques such as the standard gamble and the time trade-off technique to combine the quality and quantity of life into a single measure such as quality-adjusted life years (QALYs).

A range of previous studies have explored the relationship between obesity and generic HRQoL, such as those using the SF-36 survey.15, 16, 17, 18, 19 A consistent finding reported across these studies is the negative impact that obesity (as measured by BMI) exerts on HRQoL. Although these studies provide useful insights into the association between obesity and HRQoL, they do not provide an overall estimate of the impact of BMI on a preference-based measure of health outcomes such as QALYs.20

In recent years, however, the preference-based measurement of health outcomes has been assisted by the development of several algorithms that transform item responses from generic health questionnaires such as the SF-36 into health state utility values.21, 22, 23, 24, 25 For example, the SF-6D,20 which is a summary preference-based measure of health derived from the SF-36 questionnaire, has been used in a number of studies to examine the association between BMI and utility.8, 9, 10, 12

The purpose of this paper is to contribute to this growing body of literature by estimating for a representative general sample of the Australian population (1) the cross-sectional association between BMI and utility for individuals participating in the Household, Income and Labour Dynamics in Australia (HILDA) Survey; and (2) the longitudinal relationship between BMI and utility for respondents who participated in both the 2007 and 2009 HILDA waves.

In addition to providing recent estimates for Australia, we also correct for the presence of measurement error in self-reported height and weight, using a recently developed Australian algorithm, and provide—to our knowledge—the first initial analysis of the longitudinal relationship between BMI and utility using Australian data.

Section snippets

Data Description and Sample

Data for this study were taken from HILDA, a longitudinal survey that commenced in 2001 with a national probability sample of Australian households. We exploit data available in the 2007 and 2009 waves of the HILDA Survey, which contain detailed sociodemographic information on participants who completed the SF-36 health survey and questions relating to their height and weight and the presence of medical conditions. For a detailed discussion of the survey and sampling methods see Wooden and

Results

Table I reports the summary statistics for the 8230 men and 8258 women in the sample. Among men in the sample, 75% are overweight or obese, whereas among women 64% are overweight or obese. The mean value for the SF-6D was 0.78 for men and 0.76 for women. For men, the medical conditions with the highest reported prevalence were hypertension (16%) and arthritis (14%). For women, the medical conditions with the highest reported prevalence were arthritis (21%), hypertension (19%), and

Discussion

The results of this study indicate that utility scores are responsive to an individual's BMI. The pooled cross-sectional regression analyses indicate that BMI and the vast majority of obesity-related medical conditions have a negative impact on utility after controlling for age, education, income, smoking status, and period effect. Obese men and women (BMI ≥30) had, on average, lower utility scores than men and women within an acceptable BMI range (–0.0190 and –0.0338, respectively). These

Conclusions

Cross-sectional analysis provides evidence of a statistically negative association between BMI and utility. Longitudinal analysis, however, suggests that only a few variables—namely, the presence of arthritis and depression/anxiety—were statistically significant in predicting change in utility. Our preferred interpretation of why we did not observe a longitudinal relationship between BMI and utility is that the impact of BMI on HRQoL is likely to take several years to manifest and is thus not

Acknowledgments

This article uses unit record data from the HILDA Survey. The HILDA Project was initiated and is funded by the Australian Government Department of Families, Housing, Community Services and Indigenous Affairs (FaHCSIA) and is managed by the Melbourne Institute of Applied Economic and Social Research (MIAESR). The findings and views reported in this article, however, are those of the authors and should not be attributed to either FaHCSIA or the MIAESR. Without implication, we would also like to

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