Abstract
IntroductionTwo thirds of United States adults are overweight or obese, which puts them at higher risk of developing chronic diseases and of death compared with normal-weight individuals. However, recent studies have found that overweight and obesity by themselves may be protective in some contexts, such as hospitalization in an intensive care unit (ICU). Our objective was to determine the relation between body mass index (BMI) and mortality at 30 days and 1 year after ICU admission.MethodsWe performed a cohort analysis of 16,812 adult patients from MIMIC-II, a large database of ICU patients at a tertiary care hospital in Boston, Massachusetts. The data were originally collected during the course of clinical care, and we subsequently extracted our dataset independent of the study outcome.ResultsCompared with normal-weight patients, obese patients had 26% and 43% lower mortality risk at 30 days and 1 year after ICU admission, respectively (odds ratio (OR), 0.74; 95% confidence interval (CI), 0.64 to 0.86) and 0.57 (95% CI, 0.49 to 0.67)); overweight patients had nearly 20% and 30% lower mortality risk (OR, 0.81; 95% CI, 0.70 to 0.93) and OR, 0.68 (95% CI, 0.59 to 0.79)). Severely obese patients (BMI ≥ 40 kg/m2) did not have a significant survival advantage at 30 days (OR, 0.94; 95% CI, 0.74 to 1.20), but did have 30% lower mortality risk at 1 year (OR, 0.70 (95% CI, 0.54 to 0.90)). No significant difference in admission acuity or ICU and hospital length of stay was found across BMI categories.ConclusionOur study supports the hypothesis that patients who are overweight or obese have improved survival both 30 days and 1 year after ICU admission.
Highlights
Two thirds of United States adults are overweight or obese, which puts them at higher risk of developing chronic diseases and of death compared with normal-weight individuals
Some differences existed between the body mass index (BMI) groups with respect to various covariates, none of the differences seem to be large enough or to be of sufficient clinical importance to account for the effect of BMI on mortality
Human macrophages have been shown to switch between the M1 and M2 phenotypes during critical illness [38], so perhaps one mechanism by which overweight and obesity are protective during critical illness may be a switch from M1 proinflammatory activation to alternative M2 antiinflammatory activation in the large population of macrophages that are already present in their adipose tissue compared with normal-weight individuals
Summary
Two thirds of United States adults are overweight or obese, which puts them at higher risk of developing chronic diseases and of death compared with normal-weight individuals. Obesity is associated with a higher risk of developing chronic diseases, including diabetes, hypertension, osteoarthritis, and coronary artery disease (CAD) compared with normal weight (BMI, 18.5 to < 25 kg/m2), and epidemiologic studies have found that obese adults have significantly higher mortality than do those with a BMI between 20 and 25 kg/m2 [2]. In a separate long-term observational study on the natural progression of cardiovascular disease, researchers found that obesity did not increase the risk of organ failure or in-hospital mortality for those that developed organ failure, and that diabetes was a significant predictor of both, regardless of weight status [5]. Studies looking directly at the effect of obesity on mortality after admission to the intensive care unit (ICU) had mixed results. Oliveros and Villamor [19] reviewed 23 studies and found that overweight and obesity, but not severe obesity (BMI ≥ 40 kg/m2), were linked to lower ICU or hospital mortality (they did not separate the studies that reported ICU mortality from those that reported hospital mortality) [19], whereas Hogue and colleagues [20] reviewed 22 studies (most of which were included in the meta-analysis of Oliveros and Villamor) and found that overweight and obesity had no effect on ICU mortality but were associated with lower hospital mortality
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