Comparison of the associations between non-traditional and traditional indices of adiposity and cardiovascular mortality: an observational study of one million person-years of follow-up.

BACKGROUND/OBJECTIVE: The most widely used adiposity index, body mass index (BMI), is not optimal to evaluate cardiovascular (CV) risk associated with overweight and obesity. We aimed to explore the association between traditional and non-traditional adiposity indices and CV mortality, and compare their discriminative ability for CV death.

METHODS: We studied participants (age 19-79 years, BMI ≥18.5 kg/m2 ) from the population-based Norwegian Nord-Trøndelag Health Study 2 (HUNT 2). Traditional indices explored were BMI, waist circumference (WC) and waist- to-hip ratio, whereas non-traditional were estimated total body fat (eTBF), which is a sex-specific fat%-index, index of central obesity (WC/height) and a body shape index (ABSI) [WC/(BMI2/3  × √height)]. Associations between the traditional and non-traditional indices and CV death, obtained from the Norwegian Cause of Death Registry, were explored by Cox proportional hazard regression, and the indices' discriminative ability by Harrell's C statistics.

RESULTS: Baseline assessments were done from 1995 to 1997 and the population (n = 61,016, 52% women) was observed for 17.7 ± 4.2 years (until 2016), yielding 1,080,473.6 person-years of follow-up. Thirteen thousand one hundred and ninety five (21.6%) subjects died, of whom 4908 (37.2%) died from CV causes. Across genders, eTBF had the strongest association to CV death (unadjusted hazard ratios [HRs] 4th vs. 1st quartile in women and men 13.38 [95% confidence interval (CI): 11.05-16.22] and 9.32 [8.03-10.81], respectively), together with index of central obesity in women and ABSI in men. The other indices showed weaker associations, in particular BMI in men: 1.73 [1.56-1.93]. Age adjustment attenuated the associations, but the pattern remained. In concordance with this, C-statistics was C = 0.725 [0.713-0.737] in women and 0.711 [0.701-0.721] in men for eTBF, and C = 0.622 [0.610-0.634] in women and 0.551 [0.541-0.562] in men for BMI.

CONCLUSION: eTBF, a sex-specific total body fat index, was more strongly associated with CV death than other adiposity indices and may be a suitable clinical tool for assessment of obesity-associated CV risk.