Mendelian randomization study indicates lack of causal relationship between physical activity and lung cancer

Exploring the link between walking and lung cancer risk: a two-stage Mendelian randomization analysis

BACKGROUND

Previous observational research showed a potential link between physical activities such as walking and the risk of lung cancer. However, Mendelian randomization (MR) studies suggested there was no association between moderate to vigorous physical activity and lung cancer risk. We speculated that specific physical activities may be associated with lung cancer risk. Consequently, we conducted an MR study to examine the potential relationship between walking and the risk of lung cancer.

METHODS

We collected genetic summary data from UK Biobank. After excluding SNPs with F values less than 10 and those associated with confounding factors, we conducted a MR analysis to assess the causal effects between different types of walk and lung cancer. We also performed sensitivity analysis to validate the robustness of our findings. Finally, we analyzed the possible mediators.

RESULTS

MR analysis showed number of days/week walked for 10 + minutes was associated with a reduced risk of lung cancer risk (OR = 0.993, 95% CI = 0.987-0.998, P = 0.009). Additionally, usual walking pace was identified as a potentially significant factor in lowering the risk (OR = 0.989, 95% CI = 0.980-0.998, P = 0.015). However, duration of walks alone did not show a significant association with lung cancer risk (OR = 0.991, 95%CI = 0.977-1.005, P = 0.216). The sensitivity analysis confirmed the robustness of these findings. And number of days/week walked for 10 + minutes could affect fed-up feelings and then lung cancer risk. There was a bidirectional relationship between usual walking pace and sedentary behaviors (time spent watching TV).

CONCLUSION

The study unveiled a genetically predicted causal relationship between number of days/week walked for 10 + minutes, usual walking pace, and the risk of lung cancer. The exploration of potential mediators of walking phenotypes and their impact on lung cancer risk suggests that specific physical activities may reduce the risk of lung cancer.

Physical Activity, Sedentary Behavior, and Pancreatic Cancer Risk: A Mendelian Randomization Study

Pancreatic cancer is currently the seventh leading cause of cancer death worldwide. Understanding whether modifiable factors increase or decrease the risk of this disease is central to facilitating primary prevention. Several epidemiological studies have described the benefits of physical activity, and the risks associated with sedentary behavior, in relation to cancer. This study aimed to assess evidence of causal effects of physical activity and sedentary behavior on pancreatic cancer risk. We conducted a two-sample Mendelian randomization study using publicly available data for genetic variants associated with physical activity and sedentary behavior traits and genetic data from the Pancreatic Cancer Cohort Consortium (PanScan), the Pancreatic Cancer Case-Control Consortium (PanC4), and the FinnGen study for a total of 10 018 pancreatic cancer cases and 266 638 controls. We also investigated the role of body mass index (BMI) as a possible mediator between physical activity and sedentary traits and risk of developing pancreatic cancer. We found evidence of a causal association between genetically determined hours spent watching television (hours per day) and increased risk of pancreatic cancer for each hour increment (PanScan-PanC4 odds ratio = 1.52, 95% confidence interval 1.17-1.98, P = .002). Additionally, mediation analysis showed that genetically determined television-watching time was strongly associated with BMI, and the estimated proportion of the effect of television-watching time on pancreatic cancer risk mediated by BMI was 54%. This study reports the first Mendelian randomization-based evidence of a causal association between a measure of sedentary behavior (television-watching time) and risk of pancreatic cancer and that this is strongly mediated by BMI. Summary: Pancreatic cancer is a deadly disease that is predicted to become the second leading cause of cancer-related deaths by 2030. Physical activity and sedentary behaviors have been linked to cancer risk and survival. However, there is limited research on their correlation with pancreatic cancer. To investigate this, we used a Mendelian randomization approach to examine the genetic predisposition to physical activity and sedentariness and their relation to pancreatic cancer risk, while excluding external confounders. Our findings revealed a causal link between the time spent watching television and an increased risk of pancreatic cancer. Additionally, we determined that over half of the effect of watching television on pancreatic risk is mediated by the individual's BMI.

Heritable Traits and Lung Cancer Risk: A Two-Sample Mendelian Randomization Study

INTRODUCTION

Lung cancer is a complex polygenic disorder. Analysis with Mendelian randomization (MR) allows for genetically predicted risks to be estimated between exposures and outcomes.

METHODS

We analyzed 345 heritable traits from the United Kingdom Biobank and estimated their associated effects on lung cancer outcomes using two sample MR. In addition to estimating effects with overall lung cancer, adenocarcinoma, small cell lung cancer, and squamous cell lung cancers, we performed conditional effect modeling with multivariate MR (MVMR) and the traits of alcohol use, smoking initiation, average pre-tax income, and educational attainment.

RESULTS

Univariate MR provided evidence for increased age at first sexual intercourse (OR, 0.55; P = 6.15 × 10-13), educational attainment (OR, 0.24; P = 1.07 × 10-19), average household income (OR, 0.58; P = 7.85 × 10-05), and alcohol usually taken with meals (OR, 0.19; P = 1.06 × 10-06) associating with decreased odds of overall lung cancer development. In contrast, a lack of additional educational attainment (OR, 8.00; P = 3.48 × 10-12), body mass index (OR, 1.28; P = 9.00 × 10-08), pack years smoking as a proportion of life span (OR, 9.93; P = 7.96 × 10-12), and weekly beer intake (OR, 3.48; P = 4.08 × 10-07) were associated with an increased risk of overall lung cancer development.

CONCLUSIONS

Many heritable traits associated with an increased or inverse risk of lung cancer development. Effects vary based on histologic subtype and conditional third trait exposures.

IMPACT

We identified several heritable traits and presented their genetically predictable impact on lung cancer development, providing valuable insights for consideration.

Mendelian randomization to explore the direct or mediating associations between socioeconomic status and lung cancer

Objective

The purpose of this study was to verify whether there are direct or mediated causal associations between socioeconomic status and lung cancer.

Methods

Pooled statistics were obtained from corresponding genome-wide association studies. The inverse-variance weighted, weighted median, MR-Egger, MR-PRESSO and contamination-mixture methods were used as supplements to Mendelian randomization (MR) statistical analysis. Cochrane's Q value and the MR-Egger intercept were used for sensitivity analysis.

Results

In the univariate MR analysis, household income and education had protective effects on overall lung cancer (income: P = 5.46×10^-4; education: P = 4.79×10^-7) and squamous cell lung cancer (income: P = 2.67×10^-3; education: P = 1.42×10^-10). Smoking and BMI had adverse effects on overall lung cancer (smoking: P = 2.10×10^-7; BMI: P = 5.67×10^-4) and squamous cell lung cancer (smoking: P = 5.02×10^-6; BMI: P = 2.03×10^-7). Multivariate MR analysis found that smoking and education were independent risk factors for overall lung cancer (smoking: P = 1.96×10^-7; education: P = 3.11×10^-3), while smoking was an independent risk factor for squamous cell lung cancer (P = 2.35×10^-6). Smoking, education, and household income mediate the effect of BMI on overall lung cancer (smoking 50.0%, education 49.2%, income 25.3%) and squamous cell lung cancer (smoking 34.8%, education 30.8%, income 21.2%). Smoking, education, and BMI mediate the effect of income on overall lung cancer (smoking 13.9%, education 54.8%, BMI 9.4%) and squamous cell lung cancer (smoking 12.6%, education 63.3%, BMI 11.6%). Smoking, BMI, and income mediate the effect of education on squamous cell lung cancer (smoking 24.0%, BMI 6.2%, income 19.4%).

Conclusion

Income, education, BMI, and smoking are causally associated with both overall lung cancer and squamous cell lung cancer. Smoking and education are independent association factors for overall lung cancer, while smoking is an independent association factor for squamous cell lung cancer. Smoking and education also play important mediating roles in overall lung cancer and squamous cell lung cancer. No causal relationship was found between multiple risk factors associated with socioeconomic status and lung adenocarcinoma.

Association between physical activity and cancer risk among Chinese adults: a 10-year prospective study

BACKGROUND

In China, the quantity of physical activity differs from that in Western countries. Substantial uncertainty remains about the relevance of physical activity for cancer subtypes among Chinese adults.

OBJECTIVE

This study aimed to investigate the association between total daily physical activity and the incidence of common types of cancer.

METHODS

A total of 53,269 participants aged 30-79 years were derived from the Wuzhong subcohort of the China Kadoorie Biobank study during 2004-2008. We included 52,938 cancer-free participants in the final analysis. Incident cancers were identified through linkage with the health insurance system and death registries. Cox proportional hazard models were introduced to assess the associations of total daily physical activity with the incidence of 6 common types of cancer.

RESULTS

During a follow-up of 10.1 years, 3,674 cases of cancer were identified, including 794 (21.6%) from stomach cancer, 722 (19.7%) from lung cancer, 458 (12.5%) from colorectal cancer, 338 (9.2%) from liver cancer, 250 (6.8%) from breast cancer, and 231 (6.3%) from oesophageal cancer. Compared to the participants in the lowest quartile of physical activity levels, those in the highest quartile had an 11% lower risk for total cancer incidence (hazard ratio [HR]: 0.89, 95% confidence interval [CI]: 0.81-0.99), 25% lower risk for lung cancer incidence (HR: 0.75, 95% CI: 0.60-0.94), and 26% lower risk for colorectal cancer incidence (HR: 0.74, 95% CI: 0.55-1.00). There were significant interactions of physical activity with sex and smoking on total cancer (both P for interaction < 0.005), showing a lower risk for females and never smokers (HR: 0.92, 95% CI: 0.87-0.98 and HR: 0.93, 95% CI: 0.87-0.98, respectively).

CONCLUSIONS

Higher physical activity levels are associated with a reduced risk of total, lung, and colorectal cancer.

A bidirectional Mendelian randomization study supports the causal effects of a high basal metabolic rate on colorectal cancer risk

Purpose

We conducted a bidirectional two-sample Mendelian randomization (MR) study to determine whether genetically predicted basal metabolic rate (BMR) was a causal risk factor for colorectal cancer (CRC) or whether a genetically predicted CRC risk can influence the BMR level (i.e., reverse causation).

Methods

We employed 1,040 genetic variants as proxies for BMR to obtain effect estimates on CRC risk. Another 58 CRC-associated variants were used to estimate effects on BMR levels. Stratified analysis by tumor site was used to examine the causal associations between BMR and colon/rectal cancer risk.

Results

The inverse variance weighted (IVW) method indicated a significant causal effect of genetically determined BMR on CRC risk (OR_SD = 1.27, 95% CI = 1.07–1.51). No significant reverse causal association was identified between genetically increased CRC risk and BMR levels [IVW (β = 0, 95% CI = -0.01 to 0)]. The results of MR-Egger and the weighted median method were consistent with the IVW method. Stratified analysis by CRC sites identified significant causal associations between BMR and colon cancer [IVW (OR_SD = 1.45, 95% CI = 1.16-1-80)], and null evidence of a causal association between BMR and rectal cancer risk was found (p > 0.05).

Conclusion

Our findings add to the current literature by validating a positive relationship between high BMR levels and CRC risk instead of reverse causality. The genetically predicted BMR level was causally associated with colon cancer risk but not rectal cancer risk.

Systematic review of Mendelian randomization studies on risk of cancer

BACKGROUND

We aimed to map and describe the current state of Mendelian randomization (MR) literature on cancer risk and to identify associations supported by robust evidence.

METHODS

We searched PubMed and Scopus up to 06/10/2020 for MR studies investigating the association of any genetically predicted risk factor with cancer risk. We categorized the reported associations based on a priori designed levels of evidence supporting a causal association into four categories, namely robust, probable, suggestive, and insufficient, based on the significance and concordance of the main MR analysis results and at least one of the MR-Egger, weighed median, MRPRESSO, and multivariable MR analyses. Associations not presenting any of the aforementioned sensitivity analyses were not graded.

RESULTS

We included 190 publications reporting on 4667 MR analyses. Most analyses (3200; 68.6%) were not accompanied by any of the assessed sensitivity analyses. Of the 1467 evaluable analyses, 87 (5.9%) were supported by robust, 275 (18.7%) by probable, and 89 (6.1%) by suggestive evidence. The most prominent robust associations were observed for anthropometric indices with risk of breast, kidney, and endometrial cancers; circulating telomere length with risk of kidney, lung, osteosarcoma, skin, thyroid, and hematological cancers; sex steroid hormones and risk of breast and endometrial cancer; and lipids with risk of breast, endometrial, and ovarian cancer.

CONCLUSIONS

Despite the large amount of research on genetically predicted risk factors for cancer risk, limited associations are supported by robust evidence for causality. Most associations did not present a MR sensitivity analysis and were thus non-evaluable. Future research should focus on more thorough assessment of sensitivity MR analyses and on more transparent reporting.

Univariable and Multivariable Two-Sample Mendelian Randomization Investigating the Effects of Leisure Sedentary Behaviors on the Risk of Lung Cancer

Leisure sedentary behaviors (LSB) are widespread, and observational studies have provided emerging evidence that LSB play a role in the development of lung cancer (LC). However, the causal inference between LSB and LC remains unknown. Methods: We utilized univariable (UVMR) and multivariable two-sample Mendelian randomization (MVMR) analysis to disentangle the effects of LSB on the risk of LC. MR analysis was conducted with genetic variants from genome-wide association studies of LSB (408,815 persons from UK Biobank), containing 152 single-nucleotide polymorphisms (SNPs) for television (TV) watching, 37 SNPs for computer use, and four SNPs for driving, and LC from the International Lung Cancer Consortium (11,348 cases and 15,861 controls). Multiple sensitivity analyses were further performed to verify the causality. Results: UVMR demonstrated that genetically predisposed 1.5-h increase in LSB spent on watching TV increased the odds of LC by 90% [odds ratio (OR), 1.90; 95% confidence interval (CI), 1.44-2.50; p < 0.001]. Similar trends were observed for squamous cell lung cancer (OR, 1.97; 95%CI, 1.31-2.94; p = 0.0010) and lung adenocarcinoma (OR, 1.64; 95%CI 1.12-2.39; p = 0.0110). The causal effects remained significant after adjusting for education (OR, 1.97; 95%CI, 1.44-2.68; p < 0.001) and body mass index (OR, 1.86; 95%CI, 1.36-2.54; p < 0.001) through MVMR approach. No association was found between prolonged LSB spent on computer use and driving and LC risk. Genetically predisposed prolonged LSB was additionally correlated with smoking (OR, 1.557; 95%CI, 1.287-1.884; p < 0.001) and alcohol consumption (OR, 1.010; 95%CI, 1.004-1.016; p = 0.0016). Consistency of results across complementary sensitivity MR methods further strengthened the causality. Conclusion: Robust evidence was demonstrated for an independent, causal effect of LSB spent on watching TV in increasing the risk of LC. Further work is necessary to investigate the potential mechanisms.