Hospital costs in relation to body-mass index in 1·1 million women in England: a prospective cohort study

Abstract

Background: Excess weight is associated with poor health and increased health-care costs. However, a detailed understanding of the effects of excess weight on total hospital costs and costs for different health conditions is needed.

Methods: Women in England aged 50-64 years were recruited into the prospective Million Women Study cohort in 1996-2001 through 60 NHS breast cancer screening centres. Participants were followed up and annual hospital costs and admission rates were estimated for April 1, 2006, to March 31, 2011, in relation to body-mass index (BMI) at recruitment, overall and for categories of health conditions defined by the International Classification of Diseases 10th revision chapter of the primary diagnosis at admission. Associations of BMI with hospital costs were projected to the 2013 population of women aged 55-79 years in England.

Findings: 1 093 866 women who provided information on height and weight, had a BMI of at least 18·5 kg/m², and had no previous cancer at recruitment, were followed up for an average of 4·9 years from April 1, 2006 (12·3 years from recruitment), during which time 1·84 million hospital admissions were recorded. Annual hospital costs were lowest for women with a BMI of 20·0 kg/m² to less than 22·5 kg/m² (£567 per woman per year, 99% CI 556-577). Every 2 kg/m² increase in BMI above 20 kg/m² was associated with a 7·4% (7·1-7·6) increase in annual hospital costs. Excess weight was associated with increased costs for all diagnostic categories, except respiratory conditions and fractures. £662 million (14·6%) of the estimated £4·5 billion of total annual hospital costs among all women aged 55-79 years in England was attributed to excess weight (BMI ≥25 kg/m²), of which £517 million (78%) arose from hospital admissions with procedures. £258 million (39%) of the costs attributed to excess weight were due to musculoskeletal admissions, mainly for knee replacement surgeries.

Interpretation: Excess body weight is associated with increased hospital costs for middle-aged and older women in England across a broad range of conditions, especially knee replacement surgery and diabetes. These results provide reliable up-to-date estimates of the health-care costs of excess weight and emphasise the need for investment to tackle this public health issue.

Funding: Cancer Research UK; Medical Research Council; National Institute for Health Research.

Figure 1

Annual hospital costs per woman by category of BMI The estimates of annual costs are adjusted for age, region of recruitment, deprivation, educational qualifications, parity, age at first birth, smoking, alcohol intake, HES data year, and proportion of HES year with contributed data. Estimates are derived by averaging predicted costs over all reported participant characteristics but with HES year set at 2010–11. Annual costs are plotted against mean measured BMI within categories of self-reported BMI from the combined 2012 and 2013 Health Surveys for England (appendix p 2). The area of each square is inversely proportional to the variance of the estimate. The error bars show 99% CI. BMI=body-mass index. HES=Hospital Episode Statistics. *In UK 2012 prices.

Figure 2

Annual hospital costs attributed to overweight and obesity among women aged 55–79 years in England by diagnostic category Overweight and obesity is defined as a BMI of 25 kg/m² or more. ICD-10 chapters are ordered in the figure according to their contribution to overweight and obesity attributed costs. These estimates were derived by applying the estimates of excess costs by BMI category for each ICD-10 chapter (or combination) from the Million Women Study analysis (appendix p 11) to women aged 55–79 years in England using the Health Surveys for England 2012 and 2013 to estimate the population-level distribution of women by self-reported BMI category and UK Office for National Statistics mid-2013 population estimates (appendix p 2). We calculated excess costs relative to a BMI category of 20 kg/m² to less than 25 kg/m², estimated as a weighted average of the estimates of the two subcategories (20 kg/m² to <22·5 kg/m² and 22·5 kg/m² to <25 kg/m²). BMI=body-mass index. *Hospital admissions were categorised by health conditions (ie, ICD-10 chapter of primary diagnosis). Although diabetes could be an underlying cause of many admissions, the categories in this figure represent the health condition for which the individual ultimately receives treatment in an inpatient setting. †All chapters with fewer than 10 000 admissions (certain infectious and parasitic diseases [I]; mental and behavioural disorders [V]; diseases of the ear and mastoid process [VIII]; pregnancy, childbirth, and the puerperium [XV]; certain conditions originating in the perinatal period [XVI]; and congenital malformations, deformations, and chromosomal abnormalities [XVII]) and the remainder of chapter XIX after the separation of fractures and medical and surgical complications. ‡In UK 2012 prices.

Figure 3

Annual hospital costs attributed to overweight and obesity among women aged 55–79 years in England by types of musculoskeletal problems Overweight and obesity is defined as a BMI of 25 kg/m² or higher. These estimates were derived by applying the estimates of excess costs by BMI category for each defined subcomponent of chapter XIII (diseases of the musculoskeletal system and connective tissue) from the Million Women Study analysis to women aged 55–79 years in England using the Health Surveys for England 2012 and 2013 to estimate the population-level distribution of women by self-reported BMI category and UK Office for National Statistics mid-2013 population estimates (appendix p 2). Excess costs were calculated relative to a BMI category of 20 kg/m² to less than 25 kg/m², estimated as a weighted average of the estimates of the two subcategories (20 kg/m² to <22·5 kg/m² and 22·5 kg/m² to <25 kg/m²). ICD-10=International Classification of Disease 10th revision. OPCS=Office for Population Censuses and Surveys classification of surgical operations and procedures 4th revision. BMI=body-mass index.