Objective: We aimed to re-examine mortality risk estimates for metabolically healthy obesity by using a 'stable' healthy non-obese referent group.Design: prospective cohort studyMethods: Participants were 5,427 men and women (aged 65.9 ± 9.4 years, 45.9% men) from the English Longitudinal Study of Ageing. Obesity was defined as body mass index ≥ 30 kg/m2 (vs. non-obese as below this threshold). Based on blood pressure, HDL-cholesterol, triglycerides, glycated haemoglobin, and C-reactive protein, participants were classified as 'healthy' (0 or 1 metabolic abnormality) or 'unhealthy' (≥ 2 metabolic abnormalities).Results: 671 deaths were observed over an average follow up of 8 years. When defining the referent group based on 1 clinical assessment, the unhealthy non-obese (Hazard ratio = 1.22; 95% CI, 1.01, 1.45) and unhealthy obese (1.29; 1.05, 1.60) were at greater risk of all-cause mortality compared to the healthy non-obese, yet no excess risk was seen in the healthy obese (1.14; 0.83, 1.52). When we re-defined the referent group based on 2 clinical assessments, effect estimates were accentuated and healthy obesity was at increased risk of mortality (2.67; 1.64, 4.34).Conclusion: An unstable healthy referent group may make 'healthy obesity' appear less harmful by obscuring the benefits of remaining never obese without metabolic dysfunction.
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