Understanding the relation between BMI and mortality
Menée en Norvège et au Royaume-Uni à l'aide d'une méthode de randomisation mendélienne et de données portant sur 56 150 et 366 385 participants, cette étude analyse l'association entre l'indice de masse corporelle, la mortalité toutes causes confondues et la mortalité par cancer (durée médiane de suivi : 18,5 et 7 ans ; 12 015 et 10 344 décès)
High body fatness is an important cause of ill health.1 In a linked paper, Sun and colleagues (doi:10.1136/bmj.l1042) use two cohort studies—the Norwegian HUNT Study and the UK Biobank—to investigate further the relation between body mass index (BMI) and mortality.2 BMI is often used as a simple proxy for body fatness, because most of the variation in BMI is due to variations in body fatness. Large observational studies consistently report J shaped associations between BMI and mortality.45678 Confounding by smoking and reverse causation (whereby diseases that lead to death may cause weight loss) are important sources of bias in this estimated relation. These biases shift the apparent optimum BMI upwards and exaggerate the increased mortality at low BMIs. Studies that have attempted to control for them have generally found an optimum BMI around 22-25 in most populations,4678 but important questions remain about the BMI-mortality relation, including (...)
BMJ , commentaire, 2018