Causal associations of sarcopenia-related traits with cardiometabolic disease and Alzheimer's disease and the mediating role of insulin resistance: A Mendelian randomization study

Sarcopenia-related traits and 10 digestive system disorders: insight from genetic correlation and Mendelian randomization

Introduction

Despite observational studies suggest hypotheses indicating a potential link, the precise causal connection between sarcopenia and digestive system illnesses has not been clearly defined.

Methods

We first use Linkage Disequilibrium Score Regression (LDSC) testing to determine the genetic correlation of traits associated with sarcopenia and 10 specific gastrointestinal diseases. Subsequently, we performed a set of bidirectional Mendelian Randomization (MR) analyses to gauge the genetic inclination towards sarcopenia-related traits in relation to each gastrointestinal condition, individually, across the FinnGen, UK Biobank, and other extensive collaborative consortia. The analytical outcomes were synthesized using a fixed-effects meta-analytic model. For outcomes indicating substantial causal impacts, mediation MR analyses were executed. Additionally, a battery of sensitivity analyses was conducted to evaluate the study's strength and dependability.

Results

Our findings established a strong causal link between appendicular lean mass and gastroesophageal reflux disease (OR  =  0.8607; 95% CI: 0.8345-0.8877; p <  0.0001) and a noteworthy correlation with nonalcoholic fatty liver disease (OR  =  0.7981; 95% CI: 0.7281-0.8749; p < 0.0001), as per the meta-analysis data. We also evaluated the intermediary role of metabolic disorders in the association between appendicular lean mass and the aforementioned diseases. The intermediary effect towards gastroesophageal reflux disease is quantified as 0.0087 (95% CI, 8e-04, 0.0183), accounting for 5.9398% (95% CI, 0.5462, 12.4940%) of the overall effect. For non-alcoholic fatty liver, the intermediary impact is 0.0150 (95% CI, 0.0050, 0.0270), representing 19.7808% (95% CI, 6.5936, 35.6055%) of the total effect.

Conclusion

The findings posit that augmenting muscle mass may serve as a preventative strategy against gastroesophageal reflux disease and non-alcoholic fatty liver, highlighting the critical role of metabolic disorder management in reducing the risks of these sarcopenia-related conditions.

Casual associations between brain structure and sarcopenia: A large-scale genetic correlation and mendelian randomization study

Sarcopenia presenting a critical challenge in population-aging healthcare. The elucidation of the interplay between brain structure and sarcopenia necessitates further research. The aim of this study is to explore the casual association between brain structure and sarcopenia. Linkage disequilibrium score regression (LDSC) was conducted to estimate the genetic correlations; MR was then performed to explore the causal relationship between Brain imaging-derived phenotypes (BIDPs) and three sarcopenia-related traits: handgrip strength, walking pace, and appendicular lean mass (ALM). The main analyses were conducted using the inverse-variance weighted method. Moreover, weighted median and MR-Egger were conducted as sensitivity analyses. Genetic association between 6.41% of BIDPs and ALM was observed, and 4.68% of BIDPs exhibited causal MR association with handgrip strength, 2.11% of BIDPs were causally associated with walking pace, and 2.04% of BIDPs showed causal association with ALM. Volume of ventromedial hypothalamus was associated with increased odds of handgrip strength (OR: 1.18, 95% CI: 1.02 to 1.37) and ALM (OR: 1.05, 95% CI: 1.01 to 1.09). Mean thickness of G-pariet-inf-Angular was associated with decreased odds of handgrip strength (OR: 0.83, 95% CI: 0.70 to 0.97) and walking pace (OR: 0.97, 95% CI: 0.93 to 0.99). As part of the brain structure forward causally influences sarcopenia, which may provide new perspectives for the prevention of sarcopenia and offer valuable insights for further research on the brain-muscle axis.

Mendelian randomization evidence for the causal effect of mental well-being on healthy aging

Mental well-being relates to multitudinous lifestyle behaviours and morbidities and underpins healthy aging. Thus far, causal evidence on whether and in what pattern mental well-being impacts healthy aging and the underlying mediating pathways is unknown. Applying genetic instruments of the well-being spectrum and its four dimensions including life satisfaction, positive affect, neuroticism and depressive symptoms (n = 80,852 to 2,370,390), we performed two-sample Mendelian randomization analyses to estimate the causal effect of mental well-being on the genetically independent phenotype of aging (aging-GIP), a robust and representative aging phenotype, and its components including resilience, self-rated health, healthspan, parental lifespan and longevity (n = 36,745 to 1,012,240). Analyses were adjusted for income, education and occupation. All the data were from the largest available genome-wide association studies in populations of European descent. Better mental well-being spectrum (each one Z-score higher) was causally associated with a higher aging-GIP (β [95% confidence interval (CI)] in different models ranging from 1.00 [0.82-1.18] to 1.07 [0.91-1.24] standard deviations (s.d.)) independent of socioeconomic indicators. Similar association patterns were seen for resilience (β [95% CI] ranging from 0.97 [0.82-1.12] to 1.04 [0.91-1.17] s.d.), self-rated health (0.61 [0.43-0.79] to 0.76 [0.59-0.93] points), healthspan (odds ratio [95% CI] ranging from 1.23 [1.02-1.48] to 1.35 [1.11-1.65]) and parental lifespan (1.77 [0.010-3.54] to 2.95 [1.13-4.76] years). Two-step Mendelian randomization mediation analyses identified 33 out of 106 candidates as mediators between the well-being spectrum and the aging-GIP: mainly lifestyles (for example, TV watching and smoking), behaviours (for example, medication use) and diseases (for example, heart failure, attention-deficit hyperactivity disorder, stroke, coronary atherosclerosis and ischaemic heart disease), each exhibiting a mediation proportion of >5%. These findings underscore the importance of mental well-being in promoting healthy aging and inform preventive targets for bridging aging disparities attributable to suboptimal mental health.

Genetically predicted type 2 diabetes mellitus mediates the causal association between plasma uric acid and ischemic stroke

OBJECTIVE

This study conducts a systematic investigation into the causal relationships between plasma uric acid levels and subtypes of ischemic stroke (IS), as well as the extent to which Type 2 diabetes mellitus (T2DM) mediates this relationship.

BACKGROUND

There is a known association between Uric acid and IS but whether they have a causal relationship remains unclear. This study aims to determine whether a genetic predisposition to uric acid is causally linked to IS, including three subtypes, and to determine the mediating role of T2DM.

METHODS

Bidirectional Mendelian randomization (MR) analyses was initially used to explore the causal relationship between uric acid and three subtypes of IS. Two-step MR methods were then used to investigate the role of T2DM in mediating the effect of uric acid and IS with its subtypes.

RESULTS

A primary analysis showed uric acid had a markedly causal association with IS (IVW, OR 1.23; 95 % CI, 1.13 - 1.34; p = 6.39 × 10-9), and two subtypes of IS, Large-vessel atherosclerotic stroke LAS (IVW, OR 1.25; 95 % CI, 1.03 - 1.53; p = 0.026) and small vessel stroke (SVS) (IVW, OR 1.20; 95 % CI, 1.00 - 1.43; p = 0.049), but not with cardioembolic stroke (CES)(IVW, OR 1.00; 95 % CI, 0.87 - 1.15; p = 0.993). Two-step MR results showed that T2DM mediated the association between uric acid and LAS and SVS, accounting for 13.85 % (p = 0.025) and 13.57 % (p = 0.028), respectively.

CONCLUSIONS

The study suggests that genetic predisposition to uric acid is linked to a greater risk of IS, especially LAS and SVS. T2DM might mediate a significant proportion of the associations between uric acid and LAS as well as SVS.

Correlation of cardiometabolic index and sarcopenia with cardiometabolic multimorbidity in middle-aged and older adult: a prospective study

Background

Research has demonstrated that sarcopenia and visceral obesity are significant risk factors for chronic disease in middle-aged and older adults. However, the relationship between sarcopenia, the cardiac metabolic index (CMI), a novel measure of visceral obesity, and cardiometabolic multimorbidity (CMM) remains unclear. In this study, data from the China Longitudinal Study of Health and Retirement (CHARLS) were analyzed to investigate the association between sarcopenia and CMI with CMM in the middle-aged and older adult population.

Methods

The study included 4,959 participants aged 45 and over. Sarcopenia was defined using the criteria of the Asian Sarcopenia Working Group 2019. CMM is defined as having two or more of the following conditions: physician-diagnosed heart disease, diabetes, stroke, and/or hypertension. CMI was calculated using the formula: CMI = (TG/HDL-C) × WHtR. To explore the association between CMI and sarcopenia and CMM, cox proportional risk regression models were used.

Results

The median age of all participants was 57 years, with 47.1% being male. Over the 8-year follow-up, 1,362 individuals developed CMM. The incidence of CMM was 8.7/1,000 person-years in the group without sarcopenia or high CMI, 17.37/1,000 person-years in those with high CMI, 14.22/1,000 person-years in the sarcopenia group, and 22.34/1,000 person-years in the group with both conditions. After adjusting for covariates, the group with both sarcopenia and high CMI had a significantly increased risk of CMM (HR 2.48, 95% CI 1.12-5.51) and heart disease (HR 2.04, 95% CI 1.05-3.98). Among those over 65 years, sarcopenia was discovered to be associated with an increased risk of CMM [HR (95% CI: 4.83 (1.22, 19.06)]. The risk of CMM was further increased to 7.31-fold (95% CI:1.72, 31.15) when combined with high CMI.

Conclusions

The combination of sarcopenia and high CMI is associated with an increased risk of developing CMM. Early identification and intervention of sarcopenia and CMI not only enable the development of targeted therapeutic strategies but also provide potential opportunities to reduce the morbidity and mortality of CMM.

The bidirectional associations between sarcopenia-related traits and cognitive performance

While many studies have sought to explore the degree to which sarcopenia-related traits are associated with cognitive performance, these studies have yielded contradictory results without any clear indication of the causality of such relationships. In efforts to better understand associations between sarcopenia-related traits and cognitive ability, a series of multivariate linear regression assessments were carried out upon datasets derived through the National Health and Nutrition Examination Survey (NHANES). Of these, cognitive performance was assessed by the Digit Symbol Substitution Test (DDST), the Consortium to Establish a Registry for Alzheimer's Disease Immediate Recall Test (CERAD-IR), Delayed Recall Test (CERAD-DR) and Animal Fluency Test (AFT). Causal relationships between the two were further inferred via a two-sample Mendelian randomization (MR) analysis approach. Sarcopenia-related traits considered in these assessments included walking speed, appendicular skeletal muscle mass (ASM), and hand grip strength (HGS). Walking speed, ASM, and HGS were all significantly independently related to cognitive scores following adjustment for covariates. MR assessments also identified that each 1-SD higher walking speed and appendicular lean mass were causally and respectively associated with a 0.34 [standard error (SE) = 0.09; p < 0.001)] standardized score higher and a 0.07 (SE = 0.01; p < 0.001) standardized score higher cognitive score, whereas a higher hand grip strength was positively associated with a better cognitive performance. Reverse MR assessments also yielded similar findings. These data suggest that lower walking speed, muscle strength, and muscle mass were all closely related to lower cognitive performance irrespective of gender, and that there may be a mutually reinforcing relationship among these variables.

An investigation into the potential association between nutrition and Alzheimer's disease

Background

Malnutrition is the most common nutritional issue in Alzheimer's disease (AD) patients, but there is still a lack of a comprehensive evaluation of the nutritional status in AD patients. This study aimed to determine the potential association of various nutritional indices with AD at different stages.

Methods

Subjects, including individuals with normal cognition (NC) and patients diagnosed with AD, were consecutively enrolled in this cross-sectional study. Demographics, body composition, dietary patterns, nutritional assessment scales and nutrition-related laboratory variables were collected. Binary logistics regression analyses and receiver operating characteristic (ROC) curves were used to indicate the association between nutrition-related variables and AD at different stages.

Results

Totals of 266 subjects, including 73 subjects with NC, 72 subjects with mild cognitive impairment due to AD (AD-MCI) and 121 subjects with dementia due to AD (AD-D) were included. There was no significant difference in dietary patterns, including Mediterranean diet and Mediterranean-DASH diet intervention for neurodegenerative delay (MIND) diet between the three groups. Lower BMI value, smaller hip and calf circumferences, lower Mini Nutritional Assessment (MNA) and Geriatric Nutritional Risk Index (GNRI) scores, and lower levels of total protein, albumin, globulin, and apolipoprotein A1 were associated with AD (all p < 0.05). Total protein and albumin levels had the greatest ability to distinguish AD from non-AD (AUC 0.80, 95% CI 0.74-0.84, p < 0.001), increased by combining calf circumference, MNA score and albumin level (AUC 0.83, 95% CI 0.77-0.88, p < 0.001). Albumin level had the greatest ability to distinguish NC from AD-MCI (AUC 0.75, 95% CI 0.67-0.82, p < 0.001), and MNA score greatest ability to distinguish AD-MCI from AD-D (AUC 0.72, 95% CI 0.65-0.78, p < 0.001).

Conclusion

Nutritional status of AD patients is significantly compromised compared with normal controls, and tends to be worsened with AD progresses. Early identification and intervention of individuals with nutritional risk or malnutrition may be significantly beneficial for reducing the risk, development, and progression of AD.

Targeting cardiac and cerebrovascular risks of sarcopenia: Is it time to screen for muscle health?

This Editorial comments on the article by Jauffret et al. in this issue.

Effect of physical activity on risk of Alzheimer's disease: A systematic review and meta-analysis of twenty-nine prospective cohort studies

OBJECTIVE

Physical activity (PA) is beneficial in reductions of all-cause mortality and dementia. However, whether Alzheimer's disease (AD) risk is modified by PA remains disputable. This meta-analysis aims to disclose the underlying relationship between PA and incident AD.

METHODS

Pubmed, Embase, Cochrane Library, and Web of Science were retrieved from inception to June 2023. Random-effects models were employed to derive the effect size, represented by hazard ratio (HR) and 95% confidence interval (CI).

RESULTS

Twenty-nine prospective cohort studies involving 2068,519 participants were included. The pooled estimate showed a favorable effect of PA on AD risk decline (HR 0.72, 95% CI 0.65-0.80). This association remained robust after adjusting for maximum confounders (HR 0.85, 95% CI 0.79-0.91). Subgroup analysis of PA intensity demonstrated an inverse dose-response relationship between PA and AD, effect sizes of which were significant in moderate (HR 0.85, 95% CI 0.80-0.93) and high PA (HR 0.56, 95% CI 0.45-0.68), but not in low PA (HR 0.94, 95% CI 0.77-1.15). Regardless of all participants or the mid-life cohort, the protection of PA against AD appeared to be valid in shorter follow-up (<15 years) rather than longer follow-up (≥15 years). In addition to follow-up, the robustness of the estimates persisted in supplementary meta-analyses, meta-regression analyses, and sensitivity analyses.

CONCLUSION

PA intervention reduces the incidence of AD, but merely in moderate to vigorous PA with follow-up of less than 15 years, thus conditionally recommending the popularization of PA as a modifiable lifestyle factor to prevent AD.