Decoding Longevity: The Dual Impact of BMI and Waist Circumference in the Oldest-Old
Recent research delves deeper into the health implications of body metrics like body mass index (BMI) and waist circumference (WC) among individuals older than 80, shedding light on their paradoxical effects on longevity. A key finding from this study is that while a higher BMI may confer protective benefits against mortality, suggesting that more body mass can be advantageous in later life, an increased WC is linked to a heightened risk of death, particularly from cardiovascular-related issues. This insight highlights the complex role body composition plays in the health and longevity of the elderly.
The study employs Mendelian randomization to provide a genetic framework, helping to distinguish the influence of these metrics from environmental and lifestyle factors. This method strengthens the credibility of the findings by minimizing confounding variables, offering a clearer picture of the direct effects of BMI and WC on health outcomes. The results are critical for developing tailored health interventions for the elderly, focusing not just on weight but more importantly on body fat distribution.
Moreover, the research encourages a nuanced approach to health monitoring in the elderly, proposing that maintaining a healthy weight while managing waist size could be key strategies for enhancing lifespan. It also calls for further studies to explore how these findings could be translated into practical guidelines for nutrition and exercise in aging populations, aiming to improve quality of life and extend years of healthy living.
Article Information
Decoding Longevity: The Dual Impact of BMI and Waist Circumference 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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