Sarah H Wild , professor of epidemiology 1 , Christopher D Byrne , professor of endocrinology and metabolism 2 3 1Centre for Population Health Sciences, Usher Institute of Population Health Sciences and Informatics, University of Edinburgh, Edinburgh, UK 2Nutrition and Metabolism, Faculty of Medicine, University of Southampton, Southampton, UK 3NIHR Southampton Biomedical Research Centre, University Hospital Southampton, Southampton, UK Correspondence to: S Wild sarah.wild{at}ed.ac.uk

People who are lean for life have the lowest mortality

The optimal body mass index (BMI) associated with lowest risk of all cause mortality is not known. As excess adiposity increases risk of conditions such as diabetes that reduce life expectancy, one might expect increasing BMI to be associated with increasing mortality. However, compared with normal weight, underweight is associated with increased mortality and modestly elevated BMI is associated with lower mortality. The former pattern is only partly explained by confounding by smoking or comorbidity, and the second observation has been called the obesity paradox.1 In addition, the influence on mortality of different patterns of weight change throughout the life course is poorly understood. Two linked papers attempt to shed light on these important subjects.2 3

Aune and colleagues (doi:10.1136/bmj.i1256) report a meta-analysis of 230 prospective studies with more than 3.74 million deaths among more than 30.3 million participants, providing further evidence that adiposity (measured by BMI) increases the risk of premature death.2 Some increase in …