Obesity measures, metabolic health and their association with 15-year all-cause and cardiovascular mortality in the SAMINOR 1 Survey: a population-based cohort study

Abstract

Background: The mortality of metabolic―obesity phenotypes has been thoroughly studied, but it is not known how the association between continuous measures of body mass index (BMI) or waist circumference differ in strata of cardiometabolic health status. Methods: We linked data on 12,815 men and women aged 36―79 years from the SAMINOR 1 Survey with mortality data from the Norwegian Cause of Death Registry. We defined metabolically healthy and unhealthy as having zero and ≥1, respectively, of the following: MetS, pre-existing diabetes or cardiovascular disease (CVD), or prescribed drugs for high blood pressure, hyperglycaemia or dyslipidaemia. We defined general and abdominal obesity as BMI ≥30 kg/m2 and waist circumference ≥88 cm (women) or 102 cm (men), respectively, and cross-classified these categories with metabolic status to create metabolically healthy non-obese and obese (MHNO and MHO) and metabolically unhealthy non-obese and obese (MUNO and MUO) phenotypes. We used Cox regression to estimate the hazard ratio (HR) for all-cause and CVD mortality for 1) the four phenotypes and 2) continuous measures of BMI and waist circumference fitted with restricted cubic splines. We adjusted for age, leisure-time physical activity, education, smoking and alcohol consumption, and tested for interactions with sex and metabolic status (only continuous measures). Results: The MHO phenotype was present in 7.8% of women and 5.8% of men. During a median follow-up of 15.3/15.2 years, 596/938 women/men had died, respectively. The MUNO and MUO group had higher mortality than the MHNO group. Sex and phenotypes interacted with respect to CVD mortality (p=0.05 for general and p=0.02 for abdominal obesity): relative to the MHNO group, the MHO group had an adjusted HR (95% confidence interval) for CVD mortality of 1.05 (0.38–2.88) in women and 2.92 (1.71–5.01) in men. We found curvilinear associations between BMI/waist circumference and all-cause mortality irrespective of metabolic status. Corresponding relationships with CVD mortality were linear and the slope differed by sex and metabolic status.Conclusion: The relationships between continuous measures of BMI/waist circumference and mortality differed by sex, metabolic status and cause of death. Poor metabolic health substantially increases mortality regardless of obesity status.