Physical activity and lung cancer among non-smokers: a pilot molecular epidemiological study within EPIC

A flexible matching strategy for matched nested case-control studies

PURPOSE

Individual matching in case-control studies improves statistical efficiency over random selection of controls but can lead to selection bias if cases are excluded due to the lack of appropriate controls or residual confounding with less strict matching criteria. We introduce flex matching, an algorithm using multiple rounds of control selection with successively relaxed matching criteria to select controls for cases.

METHODS

We simulated exposure-disease relationships in multiple cohort data sets with a range of confounding scenarios and conducted 16,800,000 nested case-control studies, comparing random selection of controls, strict matching, and flex matching. We computed average bias and statistical efficiency in estimates of exposure-disease relationships under each matching strategy.

RESULTS

On average, flex matching produced the least biased estimates of exposure-disease associations with the smallest standard errors. Strict matching algorithms that excluded cases for whom matched controls could not be identified produced biased estimates with larger standard errors. Estimates from studies with random assignment of controls were relatively unbiased, but the standard errors were larger than from studies using flex matching.

CONCLUSIONS

Flex matching should be considered for case-control designs, especially for biomarker studies where matching on technical artifacts is necessary and maximizing efficiency is a priority.

Trajectory of physical activity frequency and cancer risk: Findings from a population-based cohort study

BACKGROUND

Physical activity (PA) changes throughout an individual's life, but the association between such changes and cancer risk seems to be overlooked in the literature. Thus, this study aimed to examine the association between the trajectories of PA frequency and cancer incidence among middle-aged Korean adults.

METHODS

A total of 1,476,335 eligible participants (992,151 men and 484,184 women) aged ≥40 years from the National Health Insurance Service cohort (2002-2018) were included. Assessment of PA frequency was a self-reported measure, based on the question: "How many times per week do you perform exercise that makes you sweat?". PA frequency trajectories (i.e., trajectory classes of change in PA frequency) from 2002 to 2008 were identified using group-based trajectory modeling. Cox proportional hazards regression was used to assess the associations between the PA trajectories and cancer incidence.

RESULTS

Five PA frequency trajectories over 7 years were identified: persistently low (men:73.5%; women:74.7%), persistently moderate (men:16.2%; women:14.6%), high-to-low (men:3.9%; women:3.7%), low-to-high (men:3.5%; women:3.8%), and persistently high (men:2.9%; women:3.3%). Compared with persistently low frequency, maintaining a high PA frequency was associated with a lower risk of all cancers (Hazard ratio (HR) = 0.92, 95%CI = 0.87-0.98) and breast cancer (HR = 0.82, 95%CI = 0.70-0.96) among women. There was a lower risk for thyroid cancer among men in the high-to-low (HR = 0.83, 95%CI = 0.71-0.98), low-to-high (HR = 0.80, 95%CI = 0.67-0.96), and high PA trajectories (HR = 0.82, 95%CI = 0.68-0.99). There was a significant association between moderate trajectory and lung cancer in men (HR = 0.88, 95%CI = 0.80-0.95), in both smoking and non-smoking men.

CONCLUSION

Long-term persistent high frequency of PA as part of the daily routine should be widely promoted and encouraged to reduce the risk for all cancer development in women.

Association Between Physical Activity and Lower Risk of Lung Cancer: A Meta-Analysis of Cohort Studies

Background: Epidemiological evidences regarding the association between physical activity and the risk of lung cancer are still controversial.

Objectives: We aimed to investigate the relationship between physical activity and risk of lung cancer in men and women, as well as other high-risk populations such as cigarette smokers.

Methods: We conducted a meta-analysis of cohort studies to evaluate the association between physical activity and risk of lung cancer. Relevant studies were identified by searching PubMed and Web of Knowledge through August 2018. Study-specific relative risk (RR) with 95% confidence interval (CI) were pooled using random effect model when significant heterogeneity was detected.

Results:Twenty cohort studies with a total of 2,965,811 participants and 31,807 lung cancer cases were included. There was an inverse association between the physical activity and risk of lung cancer. Compared with the low level of physical activity, the pooled RR was 0.83 (95%CI: 0.77, 0.90), with significant heterogeneity (I² = 62.6%, P_{heterogeneity} < 0.001). The corresponding pooled RRs were 0.90 (95%CI: 0.82, 0.99) for women and 0.81 (95%CI: 0.73, 0.90) for men. Smokers with a high level of physical activity were associated with a 10% lower risk for lung cancer (RR = 0.90, 95% CI: 0.84, 0.97), while the association was not significant among non-smokers (RR = 0.95, 95% CI: 0.88, 1.03). Subgroups analysis stratified by whether the studies adjusted for smoking intensity and durations yielded the same magnitude of RR. However, the RR for subgroups without adjustment for dietary factors was 0.74 (95%CI: 0.71, 0.77), which was significantly lower than that with dietary factors adjusted (RR = 0.89, 95%CI: 0.84, 0.95).

Conclusions:Increased physical activity might be associated with lower risk of lung cancer. Such inverse association was identified among smokers rather than non-smokers. Large interventional studies are expected to further verify these findings.

A case-control study of the association between self-reported occupational and recreational physical activity and lung cancer

This case-control study with a Fujian population investigated whether self-reported occupational and recreational physical activity may be associated with lung cancer.The population comprised 1622 patients with newly diagnosed primary lung cancer and 1622 age- and gender-matched healthy controls.High-intensity occupational physical activity was associated with significantly higher risk of lung cancer (OR = 1.354, 95% CI: 1.068-1.717), especially nonsmall cell lung carcinoma (OR = 1.384, 95% CI: 1.087-1.762). Moderate or low intensity recreational physical activity was associated with reduced risk of lung cancer. The protective effect of recreational physical activity was observed in current or former smokers, but not never-smokers, and in subjects with normal or high BMI, but not low BMI, as well as people without a history of chronic lung disease. The frequency of recreational physical activity was associated with a linear reduction in the risk of lung cancer (P < .001), and also specifically nonsmall cell lung cancer (P < .001).Occupational and recreational physical activity was associated with different effects on the risk of lung cancer in a Fujian population. While recreational physical activity was associated with decreased risk of lung cancer, occupational physical activity was associated with increased risk of lung cancer.

Physical activity and lung cancer risk in men and women

PURPOSE

Although evidence has accumulated that recreational physical activities (PA) may reduce lung cancer risk, there is little evidence concerning the possible role of a potentially more important source of PA, namely occupational PA. We investigated both recreational and lifetime occupational PA in relation to lung cancer risk in a population-based case-control study in Montreal, Canada (N_CASES = 727; N_CONTROLS = 1,351).

METHODS

Unconditional logistic regression was used to estimate odds ratios (OR), separately for men and women, adjusting for smoking, exposure to occupational carcinogens, and sociodemographic and lifestyle factors.

RESULTS

In both sexes, increasing recreational PA was associated with a lower lung cancer risk (OR_MEN = 0.66, 95% confidence interval (CI) 0.47-0.92; OR_WOMEN = 0.55, 95% CI 0.34-0.88, comparing the highest versus lowest tertiles). For occupational PA, no association was observed among women, while increasing occupational PA was associated with increased risk among men (OR_MEN = 1.96, 95% CI 1.27-3.01). ORs were not modified by occupational lung carcinogen exposure, body mass index, and smoking level; results were similar across lung cancer histological types.

CONCLUSIONS

Our results support the previous findings for recreational PA and lung cancer risk. Unexpectedly, our findings suggest a positive association for occupational PA; this requires replication and more detailed investigation.

Physical activity and sedentary behavior in relation to lung cancer incidence and mortality in older women: The Women's Health Initiative

Physical activity has been associated with lower lung cancer incidence and mortality in several populations. We investigated these relationships in the Women's Health Initiative Observational Study (WHI-OS) and Clinical Trial (WHI-CT) prospective cohort of postmenopausal women. The WHI study enrolled 161,808 women aged 50-79 years between 1993 and 1998 at 40 U.S. clinical centers; 129,401 were eligible for these analyses. Cox proportional hazards models were used to assess the association of baseline physical activity levels [metabolic equivalent (MET)-min/week: none <100 (reference), low 100 to <500, medium 500 to <1,200, high 1,200+] and sedentary behavior with total lung cancer incidence and mortality. Over 11.8 mean follow-up years, 2,148 incident lung cancer cases and 1,365 lung cancer deaths were identified. Compared with no activity, higher physical activity levels at study entry were associated with lower lung cancer incidence [p = 0.009; hazard ratios (95% confidence intervals) for each physical activity category: low, HR: 0.86 (0.76-0.96); medium, HR: 0.82 (0.73-0.93); and high, HR: 0.90 (0.79-1.03)], and mortality [p < 0.0001; low, HR: 0.80 (0.69-0.92); medium, HR: 0.68 (0.59-0.80); and high, HR: 0.78 (0.66-0.93)]. Body mass index (BMI) modified the association with lung cancer incidence (p = 0.01), with a stronger association in women with BMI < 30 kg/m(2) . Significant associations with sedentary behavior were not observed. In analyses by lung cancer subtype, higher total physical activity levels were associated with lower lung cancer mortality for both overall NSCLC and adenocarcinoma. In conclusion, physical activity may be protective for lung cancer incidence and mortality in postmenopausal women, particularly in non-obese women.

Does smoking influence the physical activity and lung cancer relation? A systematic review and meta-analysis

Research suggests an inverse association between physical activity and lung cancer. However, whether the relation is modified by degree of smoking adjustment has not been summarized. We conducted a meta-analysis of physical activity and lung cancer focusing on evaluating whether smoking status and the degree of smoking adjustment influenced the association. Comparing high versus low physical activity levels from 25 observational studies yielded a lung cancer summary relative risk (RR) of 0.79 [95 % confidence interval (CI) = 0.72-0.87], with RRs of 0.87 (95 % CI = 0.80-0.94) for cohort studies and 0.57 (95 % CI = 0.46-0.71) for case-control studies. In further analyses restricted to cohort studies, physical activity was inversely related to lung cancer among former smokers (RR = 0.68, 95 % CI = 0.51-0.90) and current smokers (RR = 0.80, 95 % CI = 0.70-0.90), whereas the association was null among never smokers (RR = 1.05, 95 % CI = 0.78-1.40, p interaction = 0.26). The degree of smoking adjustment did not modify the association (p interaction = 0.73). Physical activity was unrelated to lung cancer among never smokers but it was inversely associated with lung cancer among former and current smokers. Although the physical activity and lung cancer relation was not modified by smoking status or degree of smoking adjustment, residual confounding by smoking remains a possible explanation for the relations observed.

Physical Activity and Risk of Lung Cancer: A Meta-analysis

OBJECTIVE

Previous studies concerning the association between physical activity (PA) and risk of lung cancer yielded mixed results. We investigated the association by performing a meta-analysis.

DATA SOURCES

Relevant studies were identified by searching PubMed and EMBASE to January 2014. Twelve cohort studies and 6 case-control studies involving 2 468 470 participants and 26 453 cases of lung cancer were selected for meta-analysis.

MAIN RESULTS

We calculated the summary relative risk (RR) and 95% confidence intervals (CIs) using random-effects models. The analyses showed that individuals who participated in any amount of PA had an RR of 0.79 (95% CI, 0.73-0.86) for risk of lung cancer. Those who participated in high PA (vs low PA) had an RR of 0.75 (95% CI, 0.68-0.84). Stratifying by study design (case-control and cohort studies), smoking status (current, former, and never smokers), and gender, similar inverse associations were found for all the subgroups except for never smokers subgroup.

CONCLUSIONS

Pooled results from observational studies support a protective effect of PA against lung cancer.

Household physical activity and cancer risk: a systematic review and dose-response meta-analysis of epidemiological studies

Controversial results of the association between household physical activity and cancer risk were reported among previous epidemiological studies. We conducted a meta-analysis to investigate the relationship of household physical activity and cancer risk quantitatively, especially in dose-response manner. PubMed, Embase, Web of science and the Cochrane Library were searched for cohort or case-control studies that examined the association between household physical activity and cancer risks. Random–effect models were conducted to estimate the summary relative risks (RRs), nonlinear or linear dose–response meta-analyses were performed to estimate the trend from the correlated log RR estimates across levels of household physical activity quantitatively. Totally, 30 studies including 41 comparisons met the inclusion criteria. Total cancer risks were reduced 16% among the people with highest household physical activity compared to those with lowest household physical activity (RR = 0.84, 95% CI = 0.76–0.93). The dose-response analyses indicated an inverse linear association between household physical activity and cancer risk. The relative risk was 0.98 (95% CI = 0.97–1.00) for per additional 10 MET-hours/week and it was 0.99 (95% CI = 0.98–0.99) for per 1 hour/week increase. These findings provide quantitative data supporting household physical activity is associated with decreased cancer risk in dose-response effect.

Physical activity and lung cancer prevention

Since lung cancer is among the cancers with the highest incidence and has the highest mortality rate of cancer worldwide, the means of reducing its impact are urgently needed. Emerging evidence shows that physical activity plays an etiological role in lung cancer risk reduction. The majority of studies support the fact that total and recreational physical activity reduces lung cancer risk by 20-30% for women and 20-50% for men, and there is evidence of a dose-response effect. The biological mechanisms operating between physical activity and lung cancer are likely complex and influenced by many factors including inherited or acquired susceptibility genes, gender, smoking, and other environmental factors. Several plausible biological factors and mechanisms have been hypothesized linking physical activity to reduced lung cancer risk including: improved pulmonary function, reduced concentrations of carcinogenic agents in the lungs, enhanced immune function, reduced inflammation, enhanced DNA repair capacity, changes in growth factor levels and possible gene-physical activity interactions. Future research should target the possible subgroup effects and the biologic mechanisms that may be involved.