Obesity Associated With Increased Mortality Risk
Obesity is tied to increased all-cause mortality.
Overweight and obesity appear to be associated with higher all-cause mortality and mortality related to coronary heart disease (CHD), stroke, respiratory disease, and cancer, according to data published in The Lancet.
The prevalence of obesity is increasing worldwide. According to World Health Organization (WHO) estimates, more than 1.3 bilion adults are overweight, defined as a BMI of 25.0 to 30.0, while an additional 600 million are obese, defined as a BMI of 30.0 or greater. Previous findings show that overweight, obesity, and underweight are associated with increased mortality, though it is unknown how these associations may vary across global regions. Additionally, the results may have been distorted by the inclusion of ill patients and smokers.
“Obesity is second only to smoking as a cause of premature death in Europe and North America,” study coauthor Sir Richard Peto, FRS, from the University of Oxford, Oxford, United Kingdom, said in a press release. “Smoking causes about a quarter of all premature deaths in Europe and in North America, and smokers can halve their risk of premature death by stopping. But, overweight and obesity now cause about 1 in 7 of all premature deaths in Europe and 1 in 5 of all premature deaths in North America.”
In the current study, researchers from the Global BMI Mortality Collaboration investigated the association between BMI and mortality in 3,951,455 people from 189 studies in multiple countries. They limited their analysis to individuals who were never-smokers, did not have preexisting chronic disease, and who survived the first 5 years of follow-up. Of these participants, 385,879 died during the study period, and the researchers analyzed these deaths and calculated various hazard ratios (HRs) relative to BMI.
The results show non-linear associations between all-cause mortality and BMI, including increased significance across the overweight BMI range. The HRs for the various low, normal, and overweight ranges were:
- 1.51 (95% CI, 1.43-1.59) for BMI of 15.0 to lower than 18.5
- 1.13 (95% CI, 1.09-1.17) for BMI of 18.5 to lower than 20.0
- 1.00 (95% CI, 0.98-1.02) for BMI of 20.0 to lower than 22.5
- 1.00 (95% CI, 0.99-1.01) for BMI of 22.5 to lower than 25.0
- 1.07 (95% CI, 1.07-1.08) for BMI of 25.0 to lower than 27.5
- 1.20 (95% CI, 1.18-1.22) for BMI of 27.5 to lower than 30.0
Similar to the trend observed with overweight BMI ranges, the HRs for obesity ranges were:
- 1.45 (95% CI, 1.41-1.48) for obesity grade 1 (BMI of 30.0 to lower than 35.0)
- 1.94 (95% CI, 1.87-2.01) for obesity grade 2 (BMI of 35.0 to lower than 40.0)
- 2.76 (95% CI, 2.60-2.92) for obesity grade 3 (BMI of 40.0 to lower than 60.0)
The results were similar for the overweight and obese ranges in 4 regions. Mortality increased linearly with BMI higher than 25.0, with each 5-kg/m2 increase in BMI corresponding with the following HRs:
- Europe: 1.39 (95% CI, 1.34–1.43)
- North America: 1.29 (95% CI, 1.26–1.32)
- East Asia: 1.39 (95% CI, 1.34–1.44)
- Australia and New Zealand: 1.31 (95% CI, 1.27–1.35)
These increases were observed more frequently in younger vs older participants and in men vs women. In men with obesity grade 1, the excess mortality rate was about 3 times greater than in women.
“On average, overweight people lose about 1 year of life expectancy, and moderately obese people lose about 3 years of life expectancy,” lead study author, Emanuele Di Angelantonio, MD, PhD, from the University of Cambridge, Cambridge, United Kingdom, said in a press release. “We also found that men who were obese were at much higher risk of premature death than obese women. This is consistent with previous observations that obese men have greater insulin resistance, liver fat levels, and diabetes risk than women.”
There was a non-linear association between BMI and mortality for each major cause of death in each major region included in the study, with BMI greater than 25 showing a strong positive correlation with CHD, stroke, and respiratory disease mortality, and a moderate positive correlation with cancer mortality.
An important study limitation noted by the authors is their use of BMI as the sole measure of adiposity, which did not allow them to address aspects of body composition or to consider the influence of metabolic factors.
The authors of a accompanying comment highlighted 2 additional issues raised by the study: Whether “conclusions about the relation between BMI and mortality from analyses with extensive exclusions can be generalizable and unbiased,” and “what sort of public health guidance can be obtained from analyses that pool global data,” they wrote.
- Di Angelantonio E, Bhupathiraju SN, Wormser D, et al; for The Global BMI Mortality Collaboration. Body-mass index and all-cause mortality: individual participant-data meta-analysis of 239 prospective studies in four continents. Lancet. 2016. doi:10.1016/ S0140-6736(16)30175-1.
- Berrigan D, Troiano RP, Graubard BI. BMI and mortality: the limits of epidemiological evidence. Lancet. 2016. doi:10.1016/S0140-6736(16)30949-7.