We thank Drs. Doehner and Pfeiffer (1) for their letter in response to our article (2) on the association of metabolically healthy obese (MHO) phenotype with mortality. We used five definitions of metabolic health to show that for most definitions of metabolic health both metabolically healthy and unhealthy obese patients carry a similar, elevated risk of mortality. Doehner and Pfeiffer do not question the validity of our findings in relation to the MHO phenotype, but suggest that overweight and obesity may not be harmful at older ages and in those with a chronic disease. They suggest that “weight management should be viewed with strong consideration of clinical and individual conditions” (1). We did not examine the impact of obesity on health at older ages or among those with chronic diseases. We showed obesity to be associated with greater mortality risk, irrespective of metabolic health. Another recently published study supports our finding in relation to cardiovascular disease and concludes that metabolic syndrome is no more valuable than BMI in identifying individuals at risk (3).
The BMI-mortality association appears to be complicated and subject to much debate in recent times. The Prospective Studies Collaboration (PSC) (4) used longitudinal data on 894,576 participants, showing that mortality was lowest at BMI 22.5–25 kg/m2, and each 5 kg/m2 higher BMI was associated with 30% higher overall mortality. Both overweight and obesity were associated with greater mortality in men and women and all age strata from 35 to 89 years. However, a recent meta-analysis (5) on selected published studies used BMI of 18.5−<25 kg/m2 as the reference and showed overweight (BMI of 25−<30 kg/m2) and grade 1 obesity (BMI of 30−<35 kg/m2) not to be associated with higher mortality risk. These findings were subject to much discussion on the selection of studies included in the meta-analysis and the use of 18.5−<25 kg/m2 BMI as the reference category. Recent analyses of 19 consecutive waves of data from the National Health Interview Survey (NHIS) (6) show a stronger-than-previously-estimated association between obesity and mortality risk at older ages. Thus, obesity at older ages appears to carry mortality risk.
Doehner and Pfeiffer (1) also argue against reduction of body weight in those with a chronic disease. The extent to which this conclusion is generalizable to all chronic conditions and at all ages remains to be determined. Obesity in midlife is known to be a risk factor for adverse aging outcomes, such as disability and dementia. Thus, people with chronic diseases before 65 years of age may still benefit from weight management. Better evidence that takes reverse causation and selection biases into account is needed before firm conclusions can be drawn on the impact of obesity in those with chronic diseases.
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Duality of Interest. No potential conflicts of interest relevant to this article were reported.
