Decoding Longevity: The Impact of Body Composition on Mortality in the Oldest-Old
Recent research utilizing Mendelian randomization investigates how body mass index (BMI) and waist circumference (WC) affect mortality in people over 80. This genetic approach helps clarify the long-debated "obesity paradox," where higher BMI sometimes correlates with lower mortality. In the study, higher BMI appears beneficial up to a point, suggesting an optimal range that may guard against early death, while an increased WC consistently correlates with higher mortality rates, emphasizing the complexity of body metrics in elder health.
The analysis, conducted on over 5,300 elderly Chinese participants, provides nuanced insights. Specifically, it suggests that a combination of a higher BMI with a lower WC might offer the most significant protection against death. This challenges the conventional wisdom on weight and highlights the need for tailored health guidelines for the oldest-old, taking into account the distinct roles of BMI and WC.
This work is significant as it uses genetic data to sidestep issues in previous observational studies, providing a clearer picture of how body shape and size influence longevity. It underscores the importance of precise health monitoring and personalized medical guidance for aging populations, potentially shifting public health strategies towards more customized approaches based on genetic and physiological data.
Article Information
Decoding Longevity: The Impact of Body Composition on Mortality in the Oldest-Old
Published on European Heart Journal. Yuebin Lv et al.
Abstract
Background and aims: Emerging evidence has raised an obesity paradox in observational studies of body mass index (BMI) and health among the oldest-old (aged ≥80 years), as an inverse relationship of BMI with mortality was reported. This study was to investigate the causal associations of BMI, waist circumference (WC), or both with mortality in the oldest-old people in China.
Methods: A total of 5306 community-based oldest-old (mean age 90.6 years) were enrolled in the Chinese Longitudinal Healthy Longevity Survey (CLHLS) between 1998 and 2018. Genetic risk scores were constructed from 58 single-nucleotide polymorphisms (SNPs) associated with BMI and 49 SNPs associated with WC to subsequently derive causal estimates for Mendelian randomization (MR) models. One-sample linear MR along with non-linear MR analyses were performed to explore the associations of genetically predicted BMI, WC, and their joint effect with all-cause mortality, cardiovascular disease (CVD) mortality, and non-CVD mortality.
Results: During 24 337 person-years of follow-up, 3766 deaths were documented. In observational analyses, higher BMI and WC were both associated with decreased mortality risk [hazard ratio (HR) 0.963, 95% confidence interval (CI) 0.955-0.971 for a 1-kg/m2 increment of BMI and HR 0.971 (95% CI 0.950-0.993) for each 5 cm increase of WC]. Linear MR models indicated that each 1 kg/m2 increase in genetically predicted BMI was monotonically associated with a 4.5% decrease in all-cause mortality risk [HR 0.955 (95% CI 0.928-0.983)]. Non-linear curves showed the lowest mortality risk at the BMI of around 28.0 kg/m2, suggesting that optimal BMI for the oldest-old may be around overweight or mild obesity. Positive monotonic causal associations were observed between WC and all-cause mortality [HR 1.108 (95% CI 1.036-1.185) per 5 cm increase], CVD mortality [HR 1.193 (95% CI 1.064-1.337)], and non-CVD mortality [HR 1.110 (95% CI 1.016-1.212)]. The joint effect analyses indicated that the lowest risk was observed among those with higher BMI and lower WC.
Conclusions: Among the oldest-old, opposite causal associations of BMI and WC with mortality were observed, and a body figure with higher BMI and lower WC could substantially decrease the mortality risk. Guidelines for the weight management should be cautiously designed and implemented among the oldest-old people, considering distinct roles of BMI and WC.
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