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

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.