Tackling Obesity in England - National Audit Office

TACKLING OBESITY IN ENGLANDAppendix 6 Estimatingthe cost of obesity in EnglandIntroduction1 In setting out to examine the burden of obesity, wefound that there was no authoritative estimate of the costof obesity to the National Health Service or to the widerEnglish or United Kingdom economy. We thereforeworked with health economists to develop a suitablemethodology for evaluating the costs of obesity inEngland.2 This appendix sets out the methodology, findings andconclusions from our evaluation of the direct andindirect costs of obesity in England in 1998, the latestyear for which the necessary data were available. Wecommissioned this research from Professor AlistairMcGuire, Mr Stephen Morris and Ms Maria Raikou fromthe Department of Economics at City University,London.Methodology3 We describe below the methods used to calculate thecosts of treating obesity and its consequences. Togetherthese represent the direct costs of obesity. In addition,we describe the methods used to estimate the indirectcosts arising from the effect of obesity on individuals'capacity to function in their usual role. For the purposesof this analysis, obesity was defined as a body massindex of 30 kg/m 2 or greater.Direct costs4 The direct costs of obesity were defined as the costs tothe National Health Service of treating obesity and theassociated disease that can be attributed to it. We soughtto estimate the direct costs of obesity in England in 1998by taking a prevalence-based, cost-of-illness approachbased on extensive literature review and relying onpublished primary data.Cost of treating obesity5 This covered the cost of consultations with generalpractitioners related to obesity, the cost of hospitaladmissions and outpatient attendances, and the cost ofdrugs prescribed to help obese patients lose weight. Wetook the most recent published data on the incidence ofthese events in England 52,53,54 and multiplied them byunit cost data for 1998 55 . Prescription costs for obesitywere taken from Prescription Cost Analysis reports forEngland 56 .Cost of treating the consequences of obesity6 This covered the cost of treating cases of diseases suchas coronary heart disease which can be directlyattributed to obesity. The cost of treating these diseaseswas estimated by calculating the relevant populationattributable risk proportion. We undertook a systematicreview of the literature to establish for each disease thebest data available on the proportion of that disease inthe population that was attributable to obesity, andwhich in theory would be eliminated if obesity wereeliminated. This proportion was defined by the relativerisk of developing associated diseases for individualswith obesity compared to the risk for non-obeseindividuals.7 A search of the MEDLINE database returned3,537 studies with key words for obesity and thepotentially relevant diseases. These were reviewed andreduced to 48 studies which presented data on therelative risk of disease associated with obesity, andwhich calculated this risk between discrete groups of"obese" and "non-obese" individuals defined by bodymass index (kg/m 2 ). From the 48 retained studies,17 were selected to provide data for the baselineanalysis according to the following pre-determinedhierarchical criteria:nnnassociated diseases were considered only where anincreased relative risk for obese individuals wasunequivocal;cohort studies were selected in preference to casecontrolstudies, which were selected in preference tocross-sectional studies; andlarger study samples were selected in preference tosmaller samples.8 Limited data on relative risk were available from theUnited Kingdom, so most of the data used were takenfrom international evidence, especially from the UnitedStates. The effect of this on our estimates is discussed atparagraph 24.9 To establish the cost of treating associated diseases in1998, we first obtained published data on generalpractitioner consultation rates 52 , hospital inpatientadmissions 53 , and hospital outpatient attendances 54 inEngland. These were then multiplied by published dataon unit costs 55 to derive an estimate of the NHStreatment costs for each disease. Prescription costs weretaken directly from Prescription Cost Analysis reports forEngland 56 . These cost estimates were then applied toappendix six57