Obesity may shorten life expectancy by up to 8 years and cut healthy life by up to 19 years

"Our computer modelling study shows that obesity is associated with an increased risk of developing cardiovascular disease (including heart disease and stroke) and diabetes that will, on average, dramatically reduce an individual's life expectancy and the healthy life-years free from living with these chronic illnesses compared with people of normal weight", explains Dr Steven Grover, lead author and Professor of Medicine at McGill University and a Clinical Epidemiologist at the Research Institute of the McGill University Health Centre, Montreal, Canada.

The study used data from the US National Health and Nutrition Examination Survey (NHANES; 2003--10) to create a disease-stimulation model to estimate the risk of developing diabetes and cardiovascular disease in adults of different body weight. The researchers then analysed the contribution of overweight and obesity to years of life lost and healthy years of life lost in US adults of various ages between 20 and 79 years old, compared to people of normal weight.

Overweight individuals (BMI 25 to <30 kg/m²) were estimated to lose between 0 and 3 years of life expectancy, depending on their age and gender. For obese individuals (30 to <35 kg/m²) the years lost were between 1 and 6 years, whereas the very obese (35 kg/m² or more) were estimated to lose between 1 and 8 years. The effect of excess weight on years of life lost was greatest for the young and dropped with increasing age.

Excess weight doesn't just reduce life expectancy but also healthy life-years (defined as years free of obesity-associated cardiovascular disease and diabetes). The study shows that being overweight or obese is associated with two to four times as many healthy life-years lost than total years of life lost. The highest losses in healthy life-years were in young adults aged between 20 and 29 years old, amounting to around 19 years for very obese men and women.

"The pattern is clear," says Grover. "The more an individual weighs and the younger their age, the greater the effect on their health, as they have many years ahead of them during which the increased health risks associated with obesity can negatively impact their lives."

He adds, "These clinically meaningful calculations should prove useful for obese individuals and health professionals to better appreciate the scale of the problem and the substantial benefits of a healthier lifestyle including changes to diet and regular physical activity."

Writing in a linked Comment, Dr Edward Gregg, Chief of the Epidemiology and Statistics Branch in the Division of Diabetes Translation at the Centers for Disease Control and Prevention, Atlanta, USA, says, "Meaningful metrics are needed for education, counselling, and health promotion. Some aspects of the clinical use of such estimates warrant further examination, and the ability of composite measures to differentiate the effect of small differences in thresholds of obesity levels is unclear...This... might place a higher premium on decision-making methods that can simultaneously take a lifecourse perspective, incorporate interventions, and consider individual differences so that clinicians and public health leaders alike can effectively tackle the next phases of the obesity and diabetes epidemics."