Healthcare use and costs in relation to body mass index in over one million middle-aged and older women in England

Rates of overweight and obesity worldwide have increased substantially in recent decades. In England, over 60% of adults are now overweight or obese. Because excess weight is associated with higher risks of chronic conditions, including type-2 diabetes, cardiovascular disease, osteoarthritis, and certain cancers, as well as with premature death, it constitutes a major health burden. It is also associated with higher total healthcare spending, but how the associations differ in different healthcare settings is not well understood. I undertook a systematic literature review of studies that used individual participant data to estimate annual healthcare costs in relation to body mass index (BMI; in kg/m2). Compared to adults at healthy weight (i.e. BMI 18.5 to <25 kg/m2), total annual healthcare costs were found to be 12% and 36% higher for overweight (BMI 25 to <30 kg/m2) and obese (BMI >=20 kg/m2) adults, respectively. The associations were strongest for costs of medications (18% for overweight and 68% for obese adults), followed by inpatient care costs (12% and 34%), and ambulatory care costs (4% and 26%). Most of these studies used data from the United States, and were based on small-to-moderate numbers of participants, limiting their ability to reliably estimate healthcare costs in relation to grades of obesity or for different health conditions. There was no reliable evidence from individual participant data pertaining directly to the United Kingdom. Using data on over one million middle-aged and older women in the prospective Million Women Study, linked to routine administrative data on deaths, inpatient and day-case admissions, and primary care services, I estimated annual rates and costs of hospital admissions, primary care consultations, prescription items issued, and monitoring and diagnostic tests in relation to body mass index. Every 2 kg/m2 higher BMI beyond 20 kg/m2 was associated with 7.4% higher annual hospital admission costs, 5.2% higher primary care consultation costs, and 9.9% higher prescription costs, but no clear association with test costs was identified. Projecting these results to the total population of women aged 55 to 79 years in England in 2013, 15% (£662 million) of hospital costs, 11% (£229 million) of primary care consultation costs, and 22% (£384 million) of prescription costs were attributable to overweight and obesity. Type-2 diabetes, and cardiovascular and musculoskeletal diseases were the major contributing conditions to the total excess weight attributable costs. These findings will be useful to healthcare policy makers, commissioners, and providers in making investment and prioritisation decisions, and underline calls for greater investments in cost-effective interventions to reduce excess weight and prevent weight gain.