Confounding by dietary factors in case-control studies on the efficacy of cancer screening in Japan

Not all carotenoids can reduce the risk of gastric cancer: a systematic review with meta-analysis

BACKGROUND

Gastric cancer is characterized by high invasiveness, heterogeneity, and late diagnosis, leading to high incidence and mortality rates. It is a significant public health concern globally. Early prevention is crucial in reducing the occurrence of gastric cancer, and dietary prevention, particularly focusing on carotenoids, has been considered a convenient and effective approach. However, the association between carotenoid intake and gastric cancer incidence remains controversial.

METHODS

A systematic search was conducted in PubMed, Ovid Embase, Web of Science, and Cochrane databases from inception to January 5, 2023. Two reviewers independently screened search results, extracted relevant data, and evaluated study quality. Statistical analysis was performed using the "metan" command in STATA 16 software. Random-effects or fixed-effects models were chosen based on the magnitude of heterogeneity among studies.

RESULTS

This study included a total of 35 publications, consisting of 23 case-control studies and 12 cohort studies. Meta-analysis of case-control studies showed that alpha-carotene (OR = 0.71, 95% CI: 0.55-0.92), beta-carotene (OR = 0.62, 95% CI: 0.53-0.72), and lutein (OR = 0.82, 95% CI: 0.69-0.97) significantly reduced the risk of gastric cancer, while beta-cryptoxanthin (OR = 0.88, 95% CI: 0.75-1.04) and lycopene (OR = 0.86, 95% CI: 0.73-1.00) showed no significant correlation. Meta-analysis of cohort studies indicated no significant associations between any of the five carotenoids and gastric cancer incidence (alpha-carotene: RR = 0.81, 95% CI: 0.54-1.23; beta-carotene: RR = 0.86, 95% CI: 0.64-1.16; beta-cryptoxanthin: RR = 0.86, 95% CI: 0.64-1.16; lutein: RR = 0.94, 95% CI: 0.69-1.29; lycopene: RR = 0.89, 95% CI: 0.69-1.14).

CONCLUSIONS

The relationship between carotenoids and gastric cancer incidence may vary depending on the type of study conducted. Considering that evidence from cohort studies is generally considered stronger than evidence from case-control studies, and high-quality randomized controlled trials show no significant association between carotenoids and gastric cancer incidence, current evidence does not support the supplementation of carotenoids for gastric cancer prevention. Further targeted research is needed to explore the association between the two.

Examining the Relationship between Heavy Alcohol Use and Assaults: With Adjustment for the Effects of Unmeasured Confounders

BACKGROUND

Experimental studies suggest that alcohol can lead to aggression in laboratory settings; however, it is impossible to test the causal relationship between alcohol use and real-life violence among humans in randomized clinical trials. Objectives. (i) To examine the relationship between heavy alcohol use and assaults in a population based study; (ii) to demonstrate the proxy outcome method, as a means of controlling the effects of unknown/unmeasured confounders in observational studies.

METHODS

This study used data collected from three waves of the National Survey on Drug Use and Health (NSDUH). The effects of heavy alcohol use on assault were measured using multivariable logistic regressions in conjunction with the proxy outcome method.

RESULTS

Application of the proxy outcome method indicated that effect sizes of heavy alcohol use on the risk of assault were overestimated in the standard models. After adjusting for the effects of unknown/unmeasured confounders, the risk of assault remained 43% and 63% higher (P < 0.05) among participants who consumed 5+ drinks/day for 5-8 days/month and 9-30 days/month, respectively.

CONCLUSIONS

Even after adjustment for unknown/unmeasured confounders the association between heavy alcohol use and risk of violence remained significant. These findings support the hypothesis that heavy alcohol use can cause violence.

Gastric cancer: descriptive epidemiology, risk factors, screening, and prevention

Less than a century ago, gastric cancer was the most common cancer in the United States and perhaps throughout the world. Despite its worldwide decline in incidence over the past century, gastric cancer remains a major killer across the globe. This article reviews the epidemiology, screening, and prevention of gastric cancer. We first discuss the descriptive epidemiology of gastric cancer, including its incidence, survival, mortality, and trends over time. Next, we characterize the risk factors for gastric cancer, both environmental and genetic. Serologic markers and histological precursor lesions of gastric cancer and early detection of gastric cancer using these markers are reviewed. Finally, we discuss prevention strategies and provide suggestions for further research.

Gastric cancer: descriptive epidemiology, risk factors, screening, and prevention

Less than a century ago, gastric cancer was the most common cancer in the United States and perhaps throughout the world. Despite its worldwide decline in incidence over the past century, gastric cancer remains a major killer across the globe. This article reviews the epidemiology, screening, and prevention of gastric cancer. We first discuss the descriptive epidemiology of gastric cancer, including its incidence, survival, mortality, and trends over time. Next, we characterize the risk factors for gastric cancer, both environmental and genetic. Serologic markers and histological precursor lesions of gastric cancer and early detection of gastric cancer using these markers are reviewed. Finally, we discuss prevention strategies and provide suggestions for further research.

A proxy outcome approach for causal effect in observational studies: a simulation study

BACKGROUND

Known and unknown/unmeasured risk factors are the main sources of confounding effects in observational studies and can lead to false observations of elevated protective or hazardous effects. In this study, we investigate an alternative approach of analysis that is operated on field-specific knowledge rather than pure statistical assumptions.

METHOD

The proposed approach introduces a proxy outcome into the estimation system. A proxy outcome possesses the following characteristics: (i) the exposure of interest is not a cause for the proxy outcome; (ii) causes of the proxy outcome and the study outcome are subsets of a collection of correlated variables. Based on these two conditions, the confounding-effect-driven association between the exposure and proxy outcome can then be measured and used as a proxy estimate for the effects of unknown/unmeasured confounders on the outcome of interest. Performance of this approach is tested by a simulation study, whereby 500 different scenarios are generated, with the causal factors of a proxy outcome and a study outcome being partly overlapped under low-to-moderate correlations.

RESULTS

The simulation results demonstrate that the conventional approach only led to a correct conclusion in 21% of the 500 scenarios, as compared to 72.2% for the alternative approach.

CONCLUSION

The proposed method can be applied in observational studies in social science and health research that evaluates the health impact of behaviour and mental health problems.

Cancer screening: the clash of science and intuition

The concept of early detection of cancer holds great promise and intuitive appeal. However, powerful biases can mislead clinicians when evaluating the efficacy of screening tests by clinical observation alone. Selection bias, lead-time bias, length-biased sampling, and overdiagnosis are counterintuitive concepts with critical implications for early-detection efforts. This article explains these biases and other common confounders in cancer screening. The most direct and reliable way to avoid being led astray by intuitions is through the use of randomized controlled trials.

Personality and participation in mass health checkups among Japanese community-dwelling elderly

OBJECTIVE

The aim of this study is to examine the relationship between personality traits and participation in mass health checkups among Japanese community-dwelling elderly.

METHODS

A data set of 327 men and 519 women aged 70 years and over was used in the analysis. The NEO Five-Factor Inventory was administered to assess the "big five" personality traits: neuroticism, extraversion, openness, agreeableness, and conscientiousness.

RESULTS

In multivariate logistic regression analysis adjusted for gender, age, number of years of education, living alone, presence of psychiatric diseases, presence of chronic diseases, and history of hospitalization during a 1-year period, openness was independently associated with participation in mass health checkups [odds ratio (OR)=1.51, 95% confidence interval (CI)=1.08-2.12, P<.01 and OR=1.38, 95% CI=0.96-1.97, P=.07 for the middle and highest tertile, respectively]. No other domains of personality were related to participation in the checkups.

CONCLUSIONS

The results of the present study suggest that older individuals high in openness are likely to take part in checkups for the elderly. Our findings could help improve the participation rate in mass health checkups for the prevention of long-term care dependence in later life.

A mortality comparison of participants and non-participants in a comprehensive health examination among elderly people living in an urban Japanese community

BACKGROUND AND AIMS

Recent studies have revealed that there are critical differences between participants and non-participants in health examinations. The aim of this study was to examine mortality differences between participants and non-participants in a comprehensive health examination for prevention of geriatric syndromes among community-dwelling elderly people, using a three-year prospective cohort study.

METHODS

The study population included 854 adults aged 70 to 84 at baseline. The following items were all studied: the status of participation in the comprehensive health examination as an independent variable, age, gender, number of years of education, living alone, presence of chronic diseases, experience of falls over one year, history of hospitalization over one year, self-rated health, body mass index, instrumental activities of daily living, and subjective well-being as covariates; and all-cause mortality during a three-year follow-up as a dependent variable.

RESULTS

In an adjusted Cox's proportional hazard regression model, the mortality risk for participants in the comprehensive health examination was significantly lower than that of non-participants (Risk Ratio (for participants)= 0.44, 95% confidence interval=0.24 to 0.78).

CONCLUSIONS

The present study shows that there is a large mortality difference between participants and non-participants. Our findings suggest two possible interpretations: 1) There is a bias due to self-selection for participation in the trial, which was not eliminated by adjustment for the covariates in the statistical model; 2) There is an intervention effect associated with participation in the comprehensive health examination which reduces the mortality risk.

Evaluating markers for the early detection of cancer: overview of study designs and methods

BACKGROUND

The field of cancer biomarker development has been evolving rapidly. New developments both in the biologic and statistical realms are providing increasing opportunities for evaluation of markers for both early detection and diagnosis of cancer.

PURPOSE

To review the major conceptual and methodological issues in cancer biomarker evaluation, with an emphasis on recent developments in statistical methods together with practical recommendations.

METHODS

We organized this review by type of study: preliminary performance, retrospective performance, prospective performance and cancer screening evaluation.

RESULTS

For each type of study, we discuss methodologic issues, provide examples and discuss strengths and limitations.

CONCLUSION

Preliminary performance studies are useful for quickly winnowing down the number of candidate markers; however their results may not apply to the ultimate target population, asymptomatic subjects. If stored specimens from cohort studies with clinical cancer endpoints are available, retrospective studies provide a quick and valid way to evaluate performance of the markers or changes in the markers prior to the onset of clinical symptoms. Prospective studies have a restricted role because they require large sample sizes, and, if the endpoint is cancer on biopsy, there may be bias due to overdiagnosis. Cancer screening studies require very large sample sizes and long follow-up, but are necessary for evaluating the marker as a trigger of early intervention.