Mendelian randomization as a tool for causal inference in human nutrition and metabolism

Unveiling the muscle-brain axis: A bidirectional mendelian randomization study investigating the causal relationship between sarcopenia-related traits and brain aging

BACKGROUND

Observational studies suggest an association between sarcopenia-related traits and brain aging, but whether this association reflects a causal relationship remains unclear. This study aims to employ Mendelian randomization (MR) methods to investigate the causal impact of sarcopenia-related traits on brain aging.

METHODS

This study presents a comprehensive analysis of genome-wide association study (GWAS) summary data associated with sarcopenia-related traits. The data were derived from a large-scale cohort, encompassing measures such as grip strength, lean body mass, and walking pace. Measurements of brain aging were obtained from neuroimaging genetics, utilizing meta-analysis (ENIGMA) to combine magnetic resonance imaging (MRI) data from 33,992 participants. The primary methodology employed in this analysis was the inverse-variance-weighted method (IVW). Additionally, sensitivity analyses were conducted, to assess heterogeneity and pleiotropy.

RESULT

Appendicular lean mass(ALM) is negatively correlated with Pallidum aging; Whole body fat-free mass shows a negative correlation with Amygdala aging; Leg fat-free mass (left) and Leg fat-free mass (right) are negatively correlated with Pallidum aging; Usual walking pace is positively correlated with Nucleus Accumbens aging. Cerebellum WM aging is negatively correlated with Leg fat-free mass (left) and Leg fat-free mass (right); Hippocampus aging is negatively correlated with Hand grip strength (left) and Hand grip strength (right). Ventricles aging is positively correlated with Usual walking pace; Nucleus Accumbens aging is positively correlated with Leg fat-free mass (left) and Leg fat-free mass (right); Putamen aging is positively correlated with ALM.

CONCLUSION

Our study confirms that reduced muscle mass speeds up brain aging. Walking too fast raises the risk of brain aging, while maintaining or increasing appendicular lean mass, overall muscle mass, and muscle mass in both legs lowers the risk of brain aging.

Causal relationship between metabolic syndrome and hidradenitis suppurativa: A two-sample bidirectional Mendelian randomization study

Observational studies have suggested an association between metabolic syndrome (MetS) and hidradenitis suppurativa (HS), but whether this relationship is causal remains unclear. Elucidating the causal direction could provide insights into disease mechanisms and potential interventions. We performed bidirectional two-sample Mendelian randomization (MR) using summary statistics from genome-wide association studies (GWAS) of MetS and HS. For validation, we replicated the MetS analysis using data from an independent GWAS. We applied multiple MR methods, primarily inverse variance-weighted (IVW) regression, and conducted sensitivity analyses to assess heterogeneity and pleiotropy. The MR analysis demonstrated MetS causally increased HS risk (IVW odds ratio [OR], 1.428 [95% CI, 1.193-1.710]; p < 0.001), with consistent evidence from sensitivity analyses. However, HS did not appear to causally influence MetS risk (IVW OR, 1.008 [95% CI, 0.988-1.028]; p = 0.438). This study provides evidence that MetS causally increases the risk of developing HS. However, we found no evidence for a causal relationship in the reverse direction from HS to MetS. Further research is warranted to elucidate the mechanisms underlying the identified causal association between MetS and subsequent HS development.

Investigating the causal association between systemic lupus erythematosus and migraine using Mendelian randomization analysis

OBJECTIVE

To assess whether systemic lupus erythematosus (SLE) may be genetically causally associated with migraine, including the two primary subtypes: migraine with aura (MWA) and migraine without aura (MWoA).

BACKGROUND

The association between SLE and migraine has been investigated extensively. Previous studies have shown a higher prevalence of migraine in patients with SLE, although the exact relationship remains unclear. This study investigated the potential causal association between SLE and migraine using the powerful analytical tool of Mendelian randomization (MR).

METHODS

We performed two-sample MR analysis of publicly available summary statistic datasets using inverse variance-weighted (IVW), weighted median, and MR-Egger methods based on an SLE genome-wide association study (GWAS; 5201 cases; 9066 controls; the exposure frequency is 36.5%) as an exposure and migraine GWAS (15,905 cases; 264,662 controls) in individuals with European ancestry as outcomes, focusing on the two migraine subtypes MWA (6780 cases; 264,662 controls) and MWoA (5787 cases; 264,662 controls). Thepleiotropy and heterogeneity were performed.

RESULTS

We selected 42 single-nucleotide polymorphisms from SLE GWAS as instrumental variables (IVs) for SLE on migraine, and 41 SNP IVs for SLE on MWA or MWoA. The IVW (odds ratio [OR] = 1.01, 95% confidence interval [CI] = [0.99, 1.03], p = 0.271), weighted median (OR = 1.00, 95% CI = [0.97, 1.03], p = 0.914), and MR-Egger (OR = 1.04, 95% CI = [0.99, 1.09], p = 0.153) methods showed no causal effect of SLE on migraine. A causal effect of SLE was observed on MWA (IVW: OR = 1.05, 95% CI = [1.02, 1.08], p = 0.001; weighted median: OR = 1.05, 95% CI = [1.01, 1.10], p = 0.018; MR-Egger: OR = 1.07, 95% CI = [1.01, 1.14], p = 0.035 and pIVW < 0.017 [Bonferroni correction]) but not MWoA (IVW: OR = 0.99, 95% CI = [0.96, 1.02], p = 0.331; weighted median: OR = 0.98, 95% CI = [0.94, 1.03], p = 0.496; MR-Egger: OR = 1.02, 95% CI = [0.95, 1.09], p = 0.652). The results showed no significant pleiotropy or heterogeneity.

CONCLUSION

Our MR analysis demonstrated the complex relationship between SLE and migraine, suggesting a potential effect of SLE on the risk of MWA but not MWoA. These findings can aid in the development of improved subtype-specific management of migraine in patients with SLE.

Associations between special diet and incidence risk of osteoporosis: a Mendelian randomization study

Introduction

Osteoporosis is a prevalent challenge in clinical orthopedics, affecting a significant percentage of individuals aged 50 and above. The goal of this study was to comprehensively understand the relationships between a specialized dietary regimen and the risk of developing osteoporosis.

Methods

This study employed extensive genome-wide association study (GWAS) summary statistics derived from the UK Biobank. It encompassed 8 kinds of special diets and 7 datasets pertaining to osteoporosis and associated symptoms. The principal analytical approach employed was the inverse-variance weighted method. Additionally, sensitivity analysis was employed to elucidate the diverse multiplicity patterns observed in the final model.

Results

Our results showed that there is significant evidence that a gluten-free diet is associated with osteoporosis [odds ratio (OR): 1.080, 95% confidence interval (CI): 1.048-1.112, p = 4.23E-07)]. Furthermore, there exists a suggestive link between the three distinct dietary approaches and osteoporosis [(OR: 0.949, 95%CI: 0.929-0.970, p = 3.00E-06) for comprehensive consumption; (OR: 1.053, 95%CI: 1.018-1.089, p = 2.23E-03) for abstaining from wheat consumption; (OR: 1.036, 95%CI: 1.005-1.068, p = 1.97E-02) for abstaining from sugar consumption]. No additional correlation between the special dietary regimens and osteoporosis has been observed.

Conclusion

Our research has uncovered a notable correlation between a gluten-free diet and the occurrence of osteoporosis. Furthermore, it exerts a promoting influence on the onset of osteoporosis, which stands in direct contradiction to the therapeutic principles for Celiac Disease's complications. As such, a novel association among these three elements is postulated.

Effects of immune cells on ischemic stroke and the mediating roles of metabolites

Objective

Previous studies have not shown an association between IgD-CD24-B-cell absolute count (IgD-CD24-AC) and ischemic stroke (IS). Our study aimed to assess the causal effect of IgD-CD24-AC on IS and to explore the role of ascorbic acid 2-sulfate (AA2S) as a potential mediator.

Methods

Our study was based on the largest available genome-wide association study (GWAS). Inverse variance weighting (IVW), MR-Egger, weighted median (WMN), simple mode, and weighted mode methods were used to assess causal effects, with IVW as the primary outcome. Subsequently, we further performed a two-step MR analysis to evaluate whether AA2S mediated this causal effect. In addition, several sensitivity analyses were conducted to evaluate heterogeneity, including Cochran's Q test, the MR-Egger intercept test, the MR-PRESSO global test, and the leave-one-out analysis.

Results

Using the IVW approach, the risk ratio of IgD-CD24-AC to IS was estimated to be 1.216 (95% CI = 1.079-1.371, p = 0.001). This result was supported by the WMN method (OR = 1.204, 95% CI = 1.020-1.421, p = 0.028) and the MR-Egger method (OR = 1.177, 95% CI = 0.962-1.442, p = 0.133). We also observed the same trend with the simple model and weighted model. Furthermore, the proportion of genetically predicted IgD-CD24-AC mediated through AA2S levels was 3.73%.

Conclusion

Our study revealed a causal relationship between IgD-CD24-AC and IS, a small part of which was mediated by AA2S. These findings offer critical insights for developing immune-targeted therapies in the future and lay a strong foundation for advancements in precision medicine.

Association between systemic lupus erythematosus and osteoporosis: a mendelian randomization analysis

BACKGROUND

Systemic Lupus Erythematosus (SLE) and Osteoporosis are two prevalent medical conditions. Previous studies have suggested a possible correlation between SLE and osteoporosis, though the underpinning causal relationship remains largely unknown. The current study aimed to elucidate the causal association between SLE and osteoporosis by employing a Mendelian randomization (MR) approach.

METHODS

We performed two-sample MR analysis using the inverse variance-weighted (IVW), weighted median, and MR-Egger methods on publicly available summary statistics datasets using a SLE genome-wide association study (GWAS) as an exposure and osteoporosis GWASs in people with East Asia ancestry as outcomes. The pleiotropy and heterogeneity were examined using a variety of techniques, including the MR-Egger intercept, the MR-PRESSO approach, and the Cochran's Q test.

RESULTS

We selected 26 single-nucleotide polymorphisms from a SLE GWAS as instrumental variables for osteoporosis. The IVW (p < 0.05) method results support a potential association between SLE and osteoporosis. MR-Egger intercept (p = 0.82) and MR-PRESSO global test (p = 0.80) did not suggest evidence of horizontal or directional pleiotropy. Cochran's Q test (p = 0.78) showed that there was no heterogeneity between IVs.

CONCLUSION

The results of MR analysis indicated that SLE is likely associated with an increased risk of osteoporosis incidence. Our findings highlight the need for increased awareness the potential risk of osteoporosis among SLE patients.

Association of different milk fat content with coronary artery disease and myocardial infarction risk: A Mendelian randomization study

BACKGROUND

Numerous observational studies have investigated on the correlation of whole, semi-skimmed, and skimmed milk with coronary artery disease (CAD) and myocardial infarction (MI) risk; However, no consensus has been reached and evidence on any causal links between these exposures and outcomes remains unclear. This study aimed to conduct univariate and multivariate Mendelian randomization (MR) analyses, using publicly released genome-wide association study summary statistics (GWAS) from the IEU GWAS database, to ascertain the causal association of milk with various fat content with CAD and MI risk.

METHODS

For the exposure data, 29, 15, and 30 single-nucleotide polymorphisms for whole milk, semi-skimmed milk, and skimmed milk, respectively, obtained from 360,806 Europeans, were used as instrumental variables. CAD and MI comprised 141,217 and 395,795 samples, respectively. We used inverse variance weighted (IVW), weighted median, MR-Egger regression, and MR Pleiotropy Residual Sum and Outlier analyses to determine whether pleiotropy and heterogeneity could skew the MR results. Sensitivity tests were conducted to verify the robustness of the results.

RESULTS

After adjusting for false discovery rates (FDR), we discovered proof that skimmed milk intake is a genetically predicted risk factor for CAD (odds ratio [OR] = 5.302; 95% confidence interval [CI] 2.261-12.432; P < 0.001; FDR-corrected P < 0.001) and MI (OR = 2.287; 95% CI 1.218-4.300; P = 0.010; FDR-corrected P = 0.009). Most sensitivity assessments yielded valid results. Multivariable MR for CAD and MI produced results consistent with those obtained using the IVW method. There was no causal relationship between whole or semi-skimmed milk, and CAD or MI.

CONCLUSION

Our findings indicate that the consumption of skimmed milk may increase the risk of CAD and MI. This evidence may help inform dietary recommendations for preventing cardiovascular disease. Further studies are required to elucidate the underlying mechanisms.

Serum albumin levels and risk of atrial fibrillation: a Mendelian randomization study

Objective

Although several observational studies have linked serum albumin to cardiovascular disease and considered it as an important biomarker, little is known about whether increasing or maintaining serum albumin levels can effectively improve the prognosis of patients with atrial fibrillation. Therefore, this study aims to further explore the causal relationship between serum albumin and atrial fibrillation and its potential mechanism.

Method

Using data from large-scale genome-wide association studies, we conducted a two-sample Mendelian randomization (MR) analysis and a mediation MR analysis, using serum albumin as the exposure variable and atrial fibrillation as the outcome variable. We included 486 serum metabolites as potential mediating factors. To increase the robustness of the analysis, we applied five statistical methods, including inverse variance weighted, weighted median, MR-Egger, simple mode, and weighted mode. Validate the MR results using Bayesian weighted Mendelian randomization method.

Result

The results of the MR analysis indicate a significant inverse association between genetically predicted serum albumin concentration (g/L) and the risk of atrial fibrillation (Beta = -0.172, OR = 0.842, 95% CI: 0.753-0.941, p = 0.002). Further mediation MR analysis revealed that serum albumin may mediate the causal relationship with atrial fibrillation by affecting two serum metabolites, docosatrienoate and oleate/vaccenate, and the mediating effect was significant. In addition, all our instrumental variables showed no heterogeneity and level-multiplicity in the MR analysis. To verify the stability of the results, we also conducted a sensitivity analysis using the leave-one-out method, and the results further confirmed that our findings were robust and reliable. Finally, we conducted a validation using the Bayesian weighted Mendelian randomization method, which demonstrated the reliability of our causal inference results.

Conclusion

This study strongly demonstrates the causal relationship between serum albumin and reduced risk of atrial fibrillation through genetic methods, and reveals the key mediating role of two serum metabolites in this relationship. These findings not only provide a new perspective for our understanding of the role of serum albumin in atrial fibrillation, but also provide new ideas for the prevention and treatment strategies of atrial fibrillation.

The association of appendicular lean mass and grip strength with low-density lipoprotein, very low-density lipoprotein, and high-density lipoprotein particle diameter: a Mendelian randomization study of the UK Biobank cohort

Aims

Reduced muscle mass and reduced strength are frequently associated with both alterations in blood lipids and poorer cardiometabolic outcomes in epidemiological studies; however, a causal association cannot be determined from such observations. Two-sample Mendelian randomization (MR) was applied to assess the association of genetically determined appendicular lean mass (ALM) and handgrip strength (HGS) with serum lipid particle diameter.

Methods and results

Mendelian randomization was implemented using summary-level data from the largest genome-wide association studies on ALM (n = 450 243), HGS (n = 223 315), and lipoprotein [low-density lipoprotein (LDL), very LDL (VLDL), and high-density lipoprotein (HDL)] particle diameters (n = 115 078). Inverse variance-weighted (IVW) method was used to calculate the causal estimates. Weighted median-based method, MR-Egger, and leave-one-out method were applied as sensitivity analysis. Greater ALM had a statistically significant positive effect on HDL particle diameter (MR-Egger: β = 0.055, SE = 0.031, P = 0.081; IVW: β = 0.068, SE = 0.014, P < 0.001) and a statistically significant negative effect on VLDL particle diameter (MR-Egger: β = -0.114, SE = 0.039, P = 0.003; IVW: β = -0.081, SE = 0.017, P < 0.001). Similarly, greater HGS had a statistically significant positive effect on HDL particle diameter (MR-Egger: β = 0.433, SE = 0.184, P = 0.019; IVW: β = 0.121, SE = 0.052, P = 0.021) and a statistically significant negative effect on VLDL particle diameter (MR-Egger: β = -0.416, SE = 0.163, P = 0.011; IVW: β = -0.122, SE = 0.046, P = 0.009). There was no statistically significant effect of either ALM or HGS on LDL particle diameter.

Conclusion

There were potentially causal associations between both increasing ALM and HGS and increasing HDL particle size and decreasing VLDL particle size. These causal associations may offer possibilities for interventions aimed at improving cardiovascular disease risk profile.

Associations of hyperthyroidism with epilepsy: a Mendelian randomization study

Prior studies have revealed an increased susceptibility to epilepsy in hyperthyroid individuals, but the genetic basis of the hyperthyroidism-epilepsy relationship is not fully comprehended, prompting this study to explore this potential association. We conducted a two-sample Mendelian randomization (TSMR) study to explore the relationship between hyperthyroidism and epilepsy by utilizing aggregated statistics from Genome-Wide Association Studies (GWAS). Data for hyperthyroidism were derived from a GWAS encompassing 462,933 participants, while epilepsy data were sourced from the International League Against Epilepsy (ILAE) consortium. Five distinct methods were employed for TSMR analysis, which included the inverse variance weighting method, MR Egger method, weighted median method, simple model, and weighted model. In our sensitivity analysis, we employed the MR Egger and MR PRESSO methods to assess pleiotropy, and inverse variance weighting and MR Egger in Cochran's Q statistics to assess heterogeneity. In the IEU database, utilizing the MR-Egger method, we obtained an odds ratio (OR) of 2.631 (95% CI 0.608, 9.796) with a p-value of 0.122. Meanwhile, employing the Weighted Median method yielded an OR of 1.813 (95% CI 0.786, 4.181) with a p-value of 0.163. The IVW method exhibited an OR of 1.986 (95% CI 1.127, 3.502) with a p-value of 0.018. In the assessment of heterogeneity, the MR-Egger method produced a Q statistic of 65.205, accompanied by a p-value of 0.087, while the IVW method recorded a Q statistic of 66.668 with a p-value of 0.083. The multifactorial analysis results showed an intercept term with a standard error (SE) value of 0.009 and a p-value of 0.291. In the FinnGen database, employing the MR-Egger method for all epilepsy data, we observed an OR of 0.952 (95% CI 0.831, 1.093) with a p-value of 0.539. Simultaneously, the Weighted Median method produced an OR of 0.986 (95% CI 0.953, 1.021) with a p-value of 0.423. The IVW method indicated an OR of 0.992 (95% CI 0.965, 1.019) with a p-value of 0.541. The MR-Egger method's assessment of heterogeneity resulted in a Q statistic of 2.671, associated with a p-value of 0.445, while the IVW method generated a Q statistic of 3.011 with a p-value of 0.556. The multifactorial analysis results displayed an intercept term with a SE-value of 0.019 and a p-value of 0.601. Sensitivity analysis found no evidence of horizontal pleiotropy or heterogeneity. Hyperthyroidism was found to be causally related to all epilepsy but had no effect on other types of epilepsy.

An inverse causal relationship between serum 25-hydroxyvitamin D levels and pulmonary hypertension: A two-sample Mendelian randomization study

Observational studies have confirmed that 25-hydroxyvitamin D (25(OH)D) is associated with pulmonary hypertension (PH), but the causal association between each other is unclear. Therefore, Mendelian randomization (MR) method was performed to validate the causal association between PH and serum 25(OH)D levels. The summary data for 25(OH)D and PH were from the National Human Genome Research Institute-European Bioinformatics Institute. Catalog of human genome-wide association studies and FinnGen biobank consortium. MR analysis was utilized to explore the potential causal association between PH and 25(OH)D. To evaluate this association, inverse variance weighting was considered as the primary method. Cochran's Q test, MR-Egger intercept test, and "leave-one-out" sensitivity analyses were utilized to control the pleiotropy and heterogeneity in the study. Two-sample MR analysis revealed an inverse causal relationship between 25(OH)D and PH (odds ratio: 0.376, 95% confidence interval: 0.162-0.876, p = 2.334 × 10-2). There was no significant heterogeneity and pleiotropy. The present study confirmed the inverse causal relationship between 25(OH)D and PH. This pathway may provide another treatment pathway in PH. Further studies to elucidate this pathway is indicated.

The Causal Association between Alcohol, Smoking, Coffee Consumption, and the Risk of Arthritis: A Meta-Analysis of Mendelian Randomization Studies

Objective: To evaluate the genetic causality between alcohol intake, smoking, coffee consumption, and arthritis. Methods: Mendelian randomization (MR) studies with alcohol, smoking, and coffee consumption behaviors as exposures, and osteoarthritis (OA) and rheumatoid arthritis (RA) as outcomes were retrieved from up to July 2023. Two researchers with relevant professional backgrounds independently assessed the quality and extracted data from the included studies. Meanwhile, we applied MR analyses of four lifestyle exposures and five arthritis outcomes (two for OA and three for RA) with gene-wide association study (GWAS) data that were different from the included studies, and the results were also included in the meta-analysis. Statistical analyses were performed using Stata 16.0 and R software version 4.3.1. Results: A total of 84 studies were assessed. Of these, 11 were selected for meta-analysis. As a whole, the included studies were considered to be at a low risk of bias and were of high quality. Results of the meta-analysis showed no significant genetic causality between alcohol intake and arthritis (odds ratio (OR): 1.02 (0.94-1.11)). Smoking and arthritis had a positive genetic causal association (OR: 1.44 (1.27-1.64)) with both OA (1.44 (1.22-1.71)) and RA (1.37 (1.26-1.50)). Coffee consumption and arthritis also had a positive genetic causal association (OR: 1.02 (1.01-1.03)). Results from the subgroup analysis showed a positive genetic causality between coffee consumption and both OA (OR: 1.02 (1.00-1.03)) and RA (OR: 1.56 (1.19-2.05)). Conclusion: There is positive genetic causality between smoking and coffee consumption and arthritis (OA and RA), while there is insufficient evidence for genetic causality between alcohol intake and arthritis.

Causal relationship between telomere length and epilepsy: A bidirectional Mendelian randomization study

OBJECTIVE

Observational studies have suggested a link between telomere length (TL) and epilepsy, but the direction of the effect and whether it is causal or not is still being debated. The objective of this study was to investigate the causal relationship between TL and epilepsy using Mendelian randomization (MR) analysis.

METHODS

We performed a bidirectional two-sample MR analysis using pooled statistics from genome-wide association studies (GWAS) of TL and epilepsy. Additionally, we conducted a replication analysis using data from another GWAS study on epilepsy to validate our findings. The final results were analyzed using five MR methods, with the inverse-variance weighted (IVW) method as the primary outcome. We applied methods such as radial MR, MR pleiotropy residual and outlier test and MR Steiger filters to exclude outliers. Sensitivity analyses were also conducted to assess heterogeneity and pleiotropy.

RESULTS

Our analysis found no evidence of a causal relationship between epilepsy and TL (all p-values >0.05). The sensitivity analysis confirms the robustness of these results.

SIGNIFICANCE

In summary, our study contradicts existing observational reports by not finding any evidence to support a causal relationship between epilepsy and TL. Further research is necessary to determine the underlying mechanism behind the association observed in observational studies.

Causal relationship between depression and aging: a bidirectional two-sample Mendelian randomization study

BACKGROUND

The causal relationship and the direction of the effect between depression and aging remain controversial.

METHODS

We used a bidirectional two-sample Mendelian randomization analysis to examine the relationship between depression and age proxy indicators. We obtained pooled statistics from genome-wide association studies (GWAS) on depression and the age proxy indicators. We employed five MR analysis methods to address potential biases and ensure robustness of our results, with the inverse variance weighted (IVW) method being the primary outcome. We also conducted outlier exclusion using Radial MR, MRPRESSO, and MR Steiger filters. Additionally, sensitivity analyses were performed to assess heterogeneity and pleiotropy.

RESULTS

Our MR analysis revealed that depression causally leads to shortened telomere length (β = - 0.014; P = 0.038), increased frailty index (β = 0.076; P = 0.000), and accelerated GrimAge (β = 0.249; P = 0.024). Furthermore, our findings showed that the frailty index (OR = 1.679; P = 0.001) was causally associated with an increased risk of depression. Additionally, we found that appendicular lean mass (OR = 0.929; P = 0.000) and left-hand grip strength (OR = 0.836; P = 0.014) were causally associated with a reduced risk of depression. Sensitivity analyses demonstrated the robustness of our findings.

CONCLUSIONS

Our study provides evidence that depression contributes to the accelerated aging process, resulting in decreased telomere length, increased frailty index, and accelerated GrimAge. Additionally, we found that the frailty index increases the risk of depression, while appendicular lean mass and left-handed grip strength reduce the risk of depression.

Associations of screen-based sedentary activities with all cause dementia, Alzheimer's disease, vascular dementia: a longitudinal study based on 462,524 participants from the UK Biobank

BACKGROUND

Current drug treatments for dementia aren't effective. Studying gene-environment interactions can help develop personalized early intervention strategies for Alzheimer's disease (AD). However, no studies have examined the relationship between screen-based sedentary activities and genetic susceptibility to AD risk, and further understanding of the causal relationship is also crucial.

METHODS

This study included 462,524 participants from the UK Biobank with a follow-up of 13.6 years. Participants' screen-based sedentary activities time was categorized into three groups based on recorded time: ≥ 4 h/day, 2-3 h/day, and ≤ 1 h/day. Cox proportional risk models were used to analyze the association between computer use/TV viewing groups and the risk of all-cause dementia, AD and vascular dementia (VD). Generalized linear model (GLM) were used to examine the relationship between screen-based sedentary activities and brain structure. Bidirectional Mendelian randomization (MR) was used to validate the causal relationship between TV viewing and AD.

RESULTS

Compared to TV viewing ≤ 1 h/day, 1)TV viewing 2-3 h/day was correlated with a higher risk of all-cause dementia (HR = 1.09, 95% CI:1.01-1.18, P < 0.05), and TV viewing ≥ 4 h/day was associated with a higher risk of all-cause dementia (HR = 1.29, 95% CI: 1.19-1.40, P < 0.001), AD (HR = 1.25, 95% CI:1.1-1.42, P < 0.001), and VD (HR = 1.24, 95% CI: 1.04-1.49, P < 0.05); 2) TV viewing ≥ 4 h/day was correlated with a higher AD risk at intermediate (HR = 1.34, 95% CI: 1.03-1.75, P < 0.001) and high AD genetic risk score (AD-GRS) (HR = 2.18, 95% CI: 1.65-2.87, P < 0.001);3) TV viewing 2-3 h/day [β = (-94.8), 95% CI: (-37.9) -(-151.7), P < 0.01] and TV viewing ≥ 4 h/day [β = (-92.94), 95% CI: (-17.42) -(-168.46), P < 0.05] were correlated with a less hippocampus volume. In addition, a causal effect of TV viewing times was observed on AD analyzed using MR Egger (OR = 5.618, 95%CI:1.502-21.013, P < 0.05).

CONCLUSIONS

There was a causal effect between TV viewing time and AD analyzed using bidirectional MR, and more TV viewing time exposure was correlated with a higher AD risk. Therefore, it is recommended that people with intermediate and high AD-GRS should control their TV viewing time to be less than 4 h/ day or even less than 1 h/day.

Causal Association Between Tea Consumption and Gout: A Mendelian Randomization Study

OBJECTIVE

Evidence from prospective studies on the consumption of tea and risk of gout is conflicting and limited. We aimed to investigate the potential causal effects of tea intake on gout using Mendelian randomization (MR).

METHODS

Genome-wide association studies in UK Biobank included 349 376 individuals and successfully discovered single-nucleotide polymorphisms linked to consumption of one cup of tea per day. Summary statistics from the Chronic Kidney Disease Genetics consortium included 13 179 cases and 750 634 controls for gout. Two-sample MR analyses were used to evaluate the relationship between tea consumption and gout risk. The inverse-variance weighted (IVW) method was used for primary analysis, and sensitivity analyses were also conducted to validate the potential causal effect.

RESULTS

In this study, the genetically predicted increase in tea consumption per cup was associated with a lower risk of gout in the IVW method (OR: 0.90; 95% CI: 0.82-0.98). Similar results were found in weighted median methods (OR: 0.88; 95% CI: 0.78-1.00), while no significant associations were found in MR-Egger (OR: 0.89; 95% CI: 0.71-1.11), weighted mode (OR: 0.80; 95% CI: 0.65-0.99), and simple mode (OR: 1.01; 95% CI: 0.75-1.36). In addition, no evidence of pleiotropy was detected by MR-Egger regression (P=0.95) or MR-PRESSO analysis (P=0.07).

CONCLUSION

This study provides evidence for the daily consumption of an extra cup of tea to reduce the risk of gout.

The causal effect of serum 25-hydroxyvitamin D levels on epilepsy: A two-sample Mendelian randomization study

OBJECTIVE

Observational studies have shown an association between 25-hydroxyvitamin D (25 (OH) D) and epilepsy, but it is unclear whether the association is causal. Therefore, we applied Mendelian randomization (MR) analysis to determine the causal relationship between serum 25 (OH) D levels and epilepsy.

METHODS

We conducted a two-sample Mendelian randomization (TSMR) study to investigate the association between serum 25 (OH) D levels and epilepsy using pooled statistics from genome-wide association studies (GWAS). Data for 25 (OH) D came from a GWAS comprising 417,580 participants, and data for epilepsy were obtained from the International League Against Epilepsy (ILAE) consortium. Five methods were used to analyze TSMR, including the inverse variance weighting method, MR Egger method, weighted median method, simple model, and weighted model. In the sensitivity analysis, MR Egger and MR PRESSO methods were used to test for pleiotropy, inverse variance weighting and MR Egger in Cochran's Q statistics were used to test for heterogeneity.

RESULTS

MR analyzed the relationship between 25 (OH) D and different types of epilepsy, and the results showed that a 1 standard deviation increase in natural log-transformed serum 25 (OH) D levels was associated with reduced risk for juvenile absence epilepsy (IVW OR = 0.985; 95% confidence interval [CI]: 0.971-0.999; P-value = 0.038). There was no apparent heterogeneity and horizontal gene pleiotropy.

SIGNIFICANCE

Higher serum levels of 25 (OH) D were a protective factor for adolescent absence epilepsy, but had no effect on other types of epilepsy.

Associations between diet and incidence risk of lung cancer: A Mendelian randomization study

Background

Observational studies have revealed associations between diet and lung cancer. However, it is unclear whether the association is disturbed by confounding factors. We used a two-sample Mendelian randomization (MR) method to characterize the associations between diet and the lung cancer risk (including 3 subtypes: lung adenocarcinoma (LA), squamous cell lung carcinoma (SqCLC), and small cell lung cancer (SCLC)).

Materials and methods

Data on 20 diets were screened from the UK Biobank. Lung cancer data came from a large meta-analysis of 85,716 individuals. The inverse-variance weighted method was used as the main analysis. Sensitivity analysis was also used to explain the different multiplicity patterns of the final model.

Results

Our results showed significant evidence that 3 diets were associated with lung cancer [odds ratio (OR): 0.271, 95% confidence interval (CI): 0.150–0.488, p = 1.46 × 10−4, dried fruit; OR: 3.010, 95% CI: 1.608–5.632, p = 5.70 × 10−4, beer] and SqCLC (OR: 0.135, 95% CI: 0.062–0.293, p = 2.33 × 10−5, dried fruit; OR: 0.485, 95% CI: 0.328–0.717, p = 2.9 × 10−4, cheese). There were also suggestive correlations between 5 dietary intakes and lung cancer (OR: 0.441, 95% CI: 0.250–0.778, p = 0.008, cereal; OR: 2.267, 95% CI: 1.126–4.564, p = 0.022, beef), LA (OR: 0.494, 95% CI: 0.285–0.858, p = 0.012, dried fruit; OR: 3.536, 95% CI: 1.546–8.085, p = 0.003, beer) and SCLC (OR: 0.006, 95% CI: 0.000–0.222, p = 0.039, non-oily fish; OR: 0.239, 95% CI: 0.086–0.664, p = 0.006, dried fruit). No other association between diet and lung cancer was observed.

Conclusion

Our study preliminary found that cheese, dried fruit, and beer intake were significantly associated with the risk of lung cancer or its subtypes, while cereal, beef, and non-oily fish intake were suggestively associated with the risk of lung cancer or its subtypes. Well-designed prospective studies are still needed to confirm our findings in the future.

Causal effects of fatty acids on depression: Mendelian randomization study

Objectives

Fatty acids (FA) are widely believed to play a role in the pathophysiology of depression. However, the causal relationships between FA and depression remain elusive and warrant further research. We aimed to investigate the potential causal relationship between FA [saturated fatty acids (SFA), mono-unsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA)] and the risk of depression using Mendelian randomization (MR) analysis.

Methods

We conducted a two-sample MR analysis using large-scale European-based genome-wide association studies (GWASs) summary data related to depression (n = 500,199 individuals) and FA [saturated fatty acids (SFA), mono-unsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA)] levels. MR analysis was performed using the Wald ratio and inverse variance-weighted (IVW) methods, and sensitivity analysis was conducted by the simple mode, weighted mode, weighted median method, and MR-Egger method.

Results

We found the causal effects for the levels of oleic acid (OA; OR = 1.07, p = 5.72 × 10^-4), adrenic acid (OR = 0.74, p = 1.01 × 10^-3), α-linolenic acid (ALA; OR = 2.52, p = 1.01 × 10^-3), eicosapentaenoic acid (EPA; OR = 0.84, p = 3.11 × 10^-3) on depression risk, after Bonferroni correction. The sensitivity analyses indicated similar trends. No causal effect between the levels of SFA and depression risk was observed.

Conclusion

Our study suggests that adrenic acid and EPA are protective against the risk of depression, while OA and ALA are potential risk factors for depression. Nonetheless, the underlying mechanisms that mediate the association between these FAs and depression risk should be investigated in further experiments.

Body fatness associations with cancer: evidence from recent epidemiological studies and future directions

This narrative review highlights current evidence linking greater body fatness to risk of various cancers, with focus on evidence from recent large cohort studies and pooled analyses of cohort studies as well as Mendelian randomization studies (which utilized genetic variants associated with body mass index to debrief the causal effect of higher body fatness on cancer risk). This review also provides insights into the biological mechanisms underpinning the associations. Data from both observational and Mendelian randomization studies support the associations of higher body mass index with increased risk of many cancers with the strongest evidence for digestive system cancers, including esophageal, stomach, colorectal, liver, gallbladder, and pancreatic cancer, as well as kidney, endometrial, and ovarian (weak association) cancer. Evidence from observational studies suggests that greater body fatness has contrasting effects on breast cancer risk depending on menopausal status and on prostate cancer risk depending on disease stage. Experimental and Mendelian randomization studies indicate that adiponectin, insulin, and sex hormone pathways play an important role in mediating the link between body fatness and cancer risk. The possible role of specific factors and pathways, such as other adipocytokines and hormones and the gut microbiome in mediating the associations between greater body fatness and cancer risk is yet uncertain and needs investigation in future studies. With rising prevalence of overweight and obesity worldwide, the proportion of cancer caused by excess body fatness is expected to increase. There is thus an urgent need to identify efficient ways at the individual and societal level to improve diet and physical activity patterns to reduce the burden of obesity and accompanying comorbidities, including cancer.

An Overview of Methods and Exemplars of the Use of Mendelian Randomisation in Nutritional Research

Objectives: It is crucial to elucidate the causal relevance of nutritional exposures (such as dietary patterns, food intake, macronutrients intake, circulating micronutrients), or biomarkers in non-communicable diseases (NCDs) in order to find effective strategies for NCD prevention. Classical observational studies have found evidence of associations between nutritional exposures and NCD development, but such studies are prone to confounding and other biases. This has direct relevance for translation research, as using unreliable evidence can lead to the failure of trials of nutritional interventions. Facilitated by the availability of large-scale genetic data, Mendelian randomization studies are increasingly used to ascertain the causal relevance of nutritional exposures and biomarkers for many NCDs. Methods: A narrative overview was conducted in order to demonstrate and describe the utility of Mendelian randomization studies, for individuals with little prior knowledge engaged in nutritional epidemiological research. Results: We provide an overview, rationale and basic description of the methods, as well as strengths and limitations of Mendelian randomization studies. We give selected examples from the contemporary nutritional literature where Mendelian randomization has provided useful evidence on the potential causal relevance of nutritional exposures. Conclusions: The selected exemplars demonstrate the importance of well-conducted Mendelian randomization studies as a robust tool to prioritize nutritional exposures for further investigation.

Body Mass Index and the Risk of Atrial Fibrillation: A Mendelian Randomization Study

Although observational studies have shown positive associations between body mass index (BMI) and the risk of atrial fibrillation (AF), the causal relationship is still uncertain owing to the susceptibility to confounding and reverse causation. This study aimed to examine the potential causality of BMI on AF by conducting a two-sample Mendelian randomization (TSMR) study.

METHODS

The independent genetic variants associated with BMI (n = 303) at the genome-wide significant level were derived as instrumental variables (IV) from the Genetic Investigation of Anthropometric Traits (GIANT) consortium consisting of 681,275 individuals of European ancestry. We then derived the outcome data from a GWAS meta-analysis comprised of 60,620 cases and 970,216 controls of European ancestry. The TSMR analyses were performed in five methods, namely inverse variance weighted (IVW) method, MR-Egger regression, the weighted median estimator (WME), the generalized summary data-based Mendelian randomization (GSMR), and the robust adjusted profile score (RAPS), to investigate whether BMI was causally associated with the risk of AF.

RESULTS

We found a genetically determined 1-standard deviation (SD) increment of BMI causally increased a 42.5% risk of AF (OR = 1.425; 95% CI, 1.346 to 1.509) based on the IVW method, which was consistent with the results of MR-Egger regression, WME, GSMR, as well as RAPS. The Mendelian randomization assumptions did not seem to be violated.

CONCLUSION

This study provides evidence that higher BMI causally increased the risk of AF, suggesting control of BMI and obesity for prevention of AF.

Relationship Between Plasma Vitamin C and COVID-19 Susceptibility and Severity: A Two-Sample Mendelian Randomization Study

Background

Considering the antioxidant function of Vitamin C, also called ascorbic acid, it is widely used against viral infections such as coronavirus disease (COVID-19) based on in vitro, observational, and ecological studies. Many confounding factors that can affect Vitamin C levels. Thus, the association described to date may not be causal. To determine the causal relationship between genetically predicted plasma Vitamin C and COVID-19 susceptibility and severity, we performed two-sample Mendelian randomization (MR) based on large samples.

Methods

The summary-level data for Vitamin C was obtained from a GWAS meta-analysis, which included 52,018 individuals from four studies of European ancestry. Data for COVID-19 HGI results were obtained from the meta-analysis of 35 GWASs with more than 1,000,000 subjects of European ancestry, including 32,494 cases with COVID-19 susceptibility and 1,316,207 controls, 9,986 cases with COVID-19 hospitalization and 1,877,672 controls, and 5,101 cases with COVID-19 severe disease and 1,383,241 controls. Mendelian randomization (MR) analysis was conducted to examine the effect of selected single nucleotide polymorphisms and COVID-19 susceptibility, hospitalization, disease severity. Several sensitivity analyses were performed with inverse-variance weighted (random-effect model), inverse variance weighted (fixed-effect model), weighted median, and maximum likelihood methods for estimating the causal effects.

Results

In this MR study, genetic predisposition to the levels of plasma Vitamin C was not associated with COVID-19 susceptibility (OR: 0.99, 95% CI: 0.84–1.17, P = 0.91), hospitalization (OR: 1.10, 95% CI: 0.71–1.71, P = 0.67) and severity (OR: 0.83, 95% CI: 0.43–1.59, P = 0.58). The association was consistent in complementary analyses. No potential heterogeneities and directional pleiotropies were observed for the analysis results.

Conclusion

According to our study, no correlation was observed between plasma Vitamin C levels and COVID-19 susceptibility and severity. Further studies in different ethnics are necessary to explore the potential role and mechanisms of circulating serum Vitamin C levels on COVID-19.

Role of the Microbiome in Regulating Bone Metabolism and Susceptibility to Osteoporosis

The human microbiota functions at the interface between diet, medication-use, lifestyle, host immune development and health. It is therefore closely aligned with many of the recognised modifiable factors that influence bone mass accrual in the young, and bone maintenance and skeletal decline in older populations. While understanding of the relationship between micro-organisms and bone health is still in its infancy, two decades of broader microbiome research and discovery supports a role of the human gut microbiome in the regulation of bone metabolism and pathogenesis of osteoporosis as well as its prevention and treatment. Pre-clinical research has demonstrated biological interactions between the microbiome and bone metabolism. Furthermore, observational studies and randomized clinical trials have indicated that therapeutic manipulation of the microbiota by oral administration of probiotics may influence bone turnover and prevent bone loss in humans. In this paper, we summarize the content, discussion and conclusions of a workshop held by the Osteoporosis and Bone Research Academy of the Royal Osteoporosis Society in October, 2020. We provide a detailed review of the literature examining the relationship between the microbiota and bone health in animal models and in humans, as well as formulating the agenda for key research priorities required to advance this field. We also underscore the potential pitfalls in this research field that should be avoided and provide methodological recommendations to facilitate bridging the gap from promising concept to a potential cause and intervention target for osteoporosis.

The Effect of Circulating Zinc, Selenium, Copper and Vitamin K1 on COVID-19 Outcomes: A Mendelian Randomization Study

Background & Aims: Previous results from observational, interventional studies and in vitro experiments suggest that certain micronutrients possess anti-viral and immunomodulatory activities. In particular, it has been hypothesized that zinc, selenium, copper and vitamin K1 have strong potential for prophylaxis and treatment of COVID-19. We aimed to test whether genetically predicted Zn, Se, Cu or vitamin K1 levels have a causal effect on COVID-19 related outcomes, including risk of infection, hospitalization and critical illness. Methods: We employed a two-sample Mendelian Randomization (MR) analysis. Our genetic variants derived from European-ancestry GWAS reflected circulating levels of Zn, Cu, Se in red blood cells as well as Se and vitamin K1 in serum/plasma. For the COVID-19 outcome GWAS, we used infection, hospitalization or critical illness. Our inverse-variance weighted (IVW) MR analysis was complemented by sensitivity analyses including a more liberal selection of variants at a genome-wide sub-significant threshold, MR-Egger and weighted median/mode tests. Results: Circulating micronutrient levels show limited evidence of association with COVID-19 infection, with the odds ratio [OR] ranging from 0.97 (95% CI: 0.87-1.08, p-value = 0.55) for zinc to 1.07 (95% CI: 1.00-1.14, p-value = 0.06)-i.e., no beneficial effect for copper was observed per 1 SD increase in exposure. Similarly minimal evidence was obtained for the hospitalization and critical illness outcomes with OR from 0.98 (95% CI: 0.87-1.09, p-value = 0.66) for vitamin K1 to 1.07 (95% CI: 0.88-1.29, p-value = 0.49) for copper, and from 0.93 (95% CI: 0.72-1.19, p-value = 0.55) for vitamin K1 to 1.21 (95% CI: 0.79-1.86, p-value = 0.39) for zinc, respectively. Conclusions: This study does not provide evidence that supplementation with zinc, selenium, copper or vitamin K1 can prevent SARS-CoV-2 infection, critical illness or hospitalization for COVID-19.

Mendelian Randomization Study of Causal Relationship between Omega-3 Fatty Acids and Risk of Lung Cancer

Objective

Evidence suggests that omega-3 fatty acid intake exerts a protective effect on lung cancer, but its causal association with risk of lung cancer remains uncertain. This study attempts to clarify the causal effect of omega-3 fatty acids on lung cancer utilizing genome-wide association study (GWAS) data with Mendelian randomization (MR) approach.

Methods

This study acquired omega-3 fatty acid data from the UK Biobank and data of lung cancer patients from the Consortium and International Lung Cancer Consortium (ILCCO). Single-nucleotide polymorphisms (SNPs) associated with omega-3 fatty acids were screened as instrumental variables (IVs) in line with the criteria of p < 5E - 8, linkage disequilibrium R ² > 0.001 and distance < 10000 kb. Through inverse variance weighted (IVW), MR-Egger, weighted median, simple mode, and weighted mode, causal association between omega-3 fatty acids and risk of lung cancer was evaluated. Cochran's Q test was applied for a heterogeneity test. The pleiotropy and horizontal pleiotropy among IVs were evaluated via MR-Egger regression intercept analysis.

Results

Totally, 42 SNPs associated with omega-3 fatty acids were identified as IVs. According to the results of IVW (OR (95% CI): 0.899 (0.817, 0.990), p = 0.03), MR-Egger (OR (95% CI): 0.856 (0.750, 0.977), p = 0.026), weighted median (OR (95% CI): 0.899 (0.817, 0.990), p = 0.001), simple mode (OR (95% CI): 0.901 (-0.678, 1.199), p = 0.478), and weighted mode (OR (95% CI): 0.859 (0.782, 0.944), p = 0.003), omega-3 fatty acids showed a causal association with low risk of lung cancer. No genetic pleiotropy or horizontal pleiotropy was found according to MR-Egger regression intercept analysis.

Conclusion

Our findings provide sufficient evidence that omega-3 fatty acids are causal protective factors of lung cancer. Despite this, further work is required for elucidating the potential mechanisms.

Causal Association Between Tea Consumption and Kidney Function: A Mendelian Randomization Study

Background

Causal research concerning the consumption of tea and the risk of chronic kidney disease (CKD) is limited. This study identified the potential causal effects of tea intake on CKD, the estimated glomerular filtration rate (eGFR), and albuminuria.

Methods

Genome-wide association studies (GWASs) from UK Biobank were able to identify single-nucleotide polymorphisms (SNPs) associated with an extra cup of tea each day. The summary statistics for the kidney function from the CKDGen consortium include 11,765 participants (12,385 cases of CKD) and 54,116 participants for the urinary albumin-to-creatinine ratio who were mostly of European descent. A two-sample Mendelian randomization (MR) analysis was performed to test the relationship between the selected SNPs and the risk of CKD.

Results

A total of 2,672 SNPs associated with tea consumption (p < 5 × 10^-8) were found, 45 of which were independent and usable in CKDGen. Drinking more cups of tea per day indicates a protective effect for CKD G3-G5 [odds ratio (OR) = 0.803; p = 0.004] and increases eGFR (β = 0.019 log ml/min/1.73 m² per cup per day; p = 2.21 × 10^-5). Excluding two SNPs responsible for directional heterogeneity (Cochran Q p = 0.02), a high consumption of tea was also negatively correlated with a lower risk of albuminuria (OR = 0.758; p = 0.002).

Conclusion

From the perspective of genes, causal relationships exist between daily extra cup of tea and the reduced risk of CKD and albuminuria and increased eGFR.

Causal Association Between Tea Consumption and Bone Health: A Mendelian Randomization Study

Background

Much observational research reported that tea consumption decreases the risk of osteoarthritis (OA), rheumatoid arthritis (RA), and osteoporosis (OP) which are the three major bone disorders. However, the observed correlation is inconclusive. To determine the causal relationship between genetically predicted tea intake and OA, RA, and OP, we performed a two-sample Mendelian randomization (MR) study based on large samples.

Methods

The European population's genome-wide association meta-analysis (GWAS) dataset identified SNPs associated with tea consumption was obtained from Neale Lab's analysis of UK Biobank data that comprised 349,376 participants of European ancestry. We extracted genetic data for knee OA (17,885 controls and 4,462 cases), hip OA (50,898 controls and 12,625 cases), and RA (43,923 controls and 14,361 cases) from the UK Biobank and OP cases (93083 controls and 1,175 cases) from FinnGen Data Freeze 2. A MR study was conducted to examine the effect of selected single nucleotide polymorphisms (SNPs) and OA, RA, and OP risk. Several sensitivity analyses were performed with weighted median and inverse-variance weighted methods for estimating the causal effects.

Results

In this MR study, the genetically predicted per one cup increase of tea consumption was not associated with knee OA (OR 1.11,95% CI: 0.79-1.55) using IVW with random effect. Genetic predisposition to tea consumption was not associated with hip OA (OR: 1.20, 95% CI: 0.84-1.71), RA (OR: 1.24 95% CI: 0.81-1.91), and OP (OR: 1.11, 95% CI: 0.89, 1.39). Following the sensitivity analysis, there was no potential pleiotropy.

Conclusion

According to our study, According to our study, there was no statistical power to confirm a causal relationship between tea consumption and the risk of knee OA, hip OA, RA, and OP.

Genetically Determined Serum 25-Hydroxyvitamin D Is Associated with Total, Trunk, and Arm Fat-Free Mass: A Mendelian Randomization Study

PURPOSE

Low serum vitamin D status has been associated with reduced muscle mass in observational studies although the relationship is controversial and a causal association cannot be determined from such observations. Two-sample Mendelian randomization (MR) was applied to assess the association between serum vitamin D (25(OH)D) and total, trunk, arm and leg fat-free mass (FFM).

METHODS

MR was implemented using summary-level data from the largest genome-wide association studies (GWAS) on vitamin D (n=73,699) and total, trunk, arm and leg FFM. Inverse variance weighted method (IVW) was used to estimate the causal estimates. Weighted median (WM)-based method, and MR-Egger, leave-one-out were applied as sensitivity analysis.

RESULTS

Genetically higher serum 25(OH)D levels had a positive effect on total (IVW = Beta: 0.042, p = 0.038), trunk (IVW = Beta: 0.045, p = 0.023) and arm (right arm IVW = Beta: 0.044, p = 0.002; left arm IVW = Beta: 0.05, p = 0.005) FFM. However, the association with leg FFM was not significant (right leg IVW = Beta: 0.03, p = 0.238; left leg IVW = Beta: 0.039, p = 0.100). The likelihood of heterogeneity and pleiotropy was determined to be low (statistically non-significant), and the observed associations were not driven by single SNPs. Furthermore, MR pleiotropy residual sum and outlier test did not highlight any outliers.

CONCLUSIONS

Our results illustrate the potentially causal, positive effect of serum 25(OH)D concentration on total, trunk and upper body appendicular fat-free mass.

Coffee Consumption and Cardiovascular Diseases: A Mendelian Randomization Study

Coffee consumption has been linked to a lower risk of cardiovascular disease in observational studies, but whether the associations are causal is not known. We conducted a Mendelian randomization investigation to assess the potential causal role of coffee consumption in cardiovascular disease. Twelve independent genetic variants were used to proxy coffee consumption. Summary-level data for the relations between the 12 genetic variants and cardiovascular diseases were taken from the UK Biobank with up to 35,979 cases and the FinnGen consortium with up to 17,325 cases. Genetic predisposition to higher coffee consumption was not associated with any of the 15 studied cardiovascular outcomes in univariable MR analysis. The odds ratio per 50% increase in genetically predicted coffee consumption ranged from 0.97 (95% confidence interval (CI), 0.63, 1.50) for intracerebral hemorrhage to 1.26 (95% CI, 1.00, 1.58) for deep vein thrombosis in the UK Biobank and from 0.86 (95% CI, 0.50, 1.49) for subarachnoid hemorrhage to 1.34 (95% CI, 0.81, 2.22) for intracerebral hemorrhage in FinnGen. The null findings remained in multivariable Mendelian randomization analyses adjusted for genetically predicted body mass index and smoking initiation, except for a suggestive positive association for intracerebral hemorrhage (odds ratio 1.91; 95% CI, 1.03, 3.54) in FinnGen. This Mendelian randomization study showed limited evidence that coffee consumption affects the risk of developing cardiovascular disease, suggesting that previous observational studies may have been confounded.

Causal Association of Coffee Consumption and Total, Knee, Hip and Self-Reported Osteoarthritis: A Mendelian Randomization Study

BACKGROUND

The causal association between coffee consumption and the risk of OA is limited. This study was conducted to identify the potential causal effects of coffee consumption on total, knee, hip, and self-reported OA.

METHODS

Genome-wide association studies (GWAS) of OA were derived from the UK Biobank, comprising 50,508 participants of European ancestry (10,083 with cases and 40,425 controls), and genetic data for specific diagnosed knee OA (4462 cases and 17,885 controls), hip OA (12,625 cases and 50,898 controls), and self-reported OA (12,658 cases and 50,898 controls). Primary and secondary genetic instruments (11 SNPs and 8 SNPs) were selected as instrumental variants from GWAS among 375,833 and 91,462 participants. Two-sample Mendelian randomization (MR) analyses were performed to test the effects of the selected single nucleotide polymorphisms (SNPs) and the OA risk. The causal effects were primarily estimated using weighted median and inverse-variance weighted method with several sensitivity analyses.

RESULTS

The MR analyses suggested that genetically predicted 1% increase of coffee consumption was associated with an increased risk of overall OA (OR:1.009, 95% CI:1.003-1.016), knee OA (OR:1.023, 95% CI:1.009-1.038), self-reported OA (OR:1.007, 95% CI:1.003-1.011), but not hip OA (OR: 1.012, 95%CI:0.999-1.024) using primary genetic instruments. Similar results were found when using secondary genetic instruments that genetically predicted coffee consumption (cups/day). Additionally, the sensitivity analyses for leave-one-out methods supported a robust association between exposure traits and OA.

CONCLUSION

Our findings indicate that genetically predicted coffee consumption exerts a causal effect on total, knee, and self-reported OA risk, but not at the hip. Further research is required to unravel the role of coffee consumption in OA prevention.