Overweight and obesity in the mortality rate data: current evidence and research issues

PURPOSE: The relation between indicators of overweight (body mass index (BMI)) and all-cause mortality and factors that potentially affect such a relationship were reviewed. METHODS: The literature was reviewed. RESULTS: Although there are many reports on the relationship between indicators of overweight (such as BMI) and all-cause mortality, there are no two studies that have been analyzed identically. It is now usually assumed that there is a U- or J-shaped association between BMI and mortality, but there are many issues that remain unsolved until today. These issues include the effects of: adequate control for cigarette smoking; adequate control for (sub)clinical disease at baseline; adequate control for intermediate risk factors; adequate measures for exposure to obesity; age, period, and cohort effects; adequate control for underlying lifestyle factors; adequate control or stratification for ethnicity and socioeconomic status; effects of sample size and duration of follow-up; and reliance on self-reported body weight and height. CONCLUSION: The literature is dominated by studies in young adult and middle-aged white inhabitants of North America and Europe. In those populations, it seems well accepted that lowest mortality is in the range of BMI between 18.5 and 25 kg.m(-2). When BMI reached values of 30 kg x m(-2) or more, mortality is substantially elevated by about 50-150%. These results may not be generalizable to other populations, and more studies are needed. All evidence is of category C (observational studies).