Obesity is a crucial risk factor for asthma. Observational studies have examined the association between abdominal obesity and asthma symptoms. This study aimed to investigate the causal relationship between visceral adipose tissue (VAT) and asthma and its potential as an independent indicator. This study utilized data from the National Health and Nutrition Examination Survey spanning 2011–8. Multivariable logistic regression and stratified variable selection were employed to identify associations between asthma and VAT. Moreover, a two-sample Mendelian randomization analysis, using 221 genetic variants as instrumental variables, was conducted to assess this relationship further. Our findings indicated that individuals with higher VAT levels were more likely to develop asthma. Visceral obesity remained a significant risk factor for asthma after adjusting for demographic characteristics. Genetic predictions suggest a positive association between VAT and an elevated risk of asthma (odds ratio [OR] = 1.393, 95% confidence interval [CI]: 1.266–1.534, and P = 1.43E−11). No significant polymorphisms were detected using the Mendelian randomization-Egger intercept test. This study presents potential evidence supporting the causal role of VAT in asthma development. Furthermore, the findings from the Mendelian randomization analysis further reinforce the relationship between VAT and asthma risk. What is already known on this topic Obesity is a well-established risk factor for asthma, with previous observational studies examining the association between abdominal obesity and asthma symptoms. What this study adds Individuals with higher visceral fat are more likely to develop asthma. Furthermore, even after adjusting for demographic factors, visceral obesity remains a significant risk factor for asthma. How this study might affect research, practice, or policy This study offers additional evidence associating visceral fat with asthma and further validates the causal relationship between the two conditions.

(1) Background: Frailty is a major geriatric syndrome associated with adverse health outcomes, while direct assessment of cardiorespiratory fitness (CRF) is often impractical in routine clinical settings. This study investigated the association between estimated cardiorespiratory fitness (eCRF) and incident frailty in middle-aged and older adults from three nationally representative aging cohorts. (2) Methods: We analyzed longitudinal data from the Health and Retirement Study (HRS; 2006–2020) in the United States, the English Longitudinal Study of Ageing (ELSA; 2004–2018) in England, and the China Health and Retirement Longitudinal Study (CHARLS; 2011–2018) in China. Participants aged 50 years or older were included. eCRF was calculated using validated sex-specific non-exercise algorithms. Frailty was assessed using a 30-item Frailty Index (FI), and incident frailty was defined as FI ≥ 0.25. Cox proportional hazards models were used to evaluate the association between baseline eCRF and incident frailty. (3) Results: A total of 8152 participants (3982 women and 4170 men) were included in the longitudinal analysis. Each 1-SD increase in eCRF was associated with a lower risk of incident frailty in HRS (HR = 0.60, 95% CI: 0.54–0.68), ELSA (HR = 0.54, 95% CI: 0.46–0.64), and CHARLS (HR = 0.74, 95% CI: 0.63–0.87). Compared with the low-eCRF group, the moderate- and high-eCRF groups had progressively lower risks of incident frailty across all three cohorts, indicating a graded inverse dose–response relationship. Findings were generally consistent across subgroup and sensitivity analyses. (4) Conclusions: Higher eCRF was associated with a lower risk of incident frailty among middle-aged and older adults across three nationally representative cohorts. As an accessible, non-invasive metric, eCRF may be useful for identifying individuals at elevated risk of incident frailty.