Mortality reduction from quitting smoking in Hong Kong: population-wide proportional mortality study

Cancer Risk Following Smoking Cessation in Korea

Importance

Tobacco smoking is associated with increased risk of various cancers, and smoking cessation has been associated with reduced cancer risks, but it is still unclear how many years of smoking cessation are required to significantly reduce the cancer risk. Therefore, investigating the association of smoking cessation with cancer is essential.

Objective

To investigate the time course of cancer risk according to the time elapsed since smoking cessation and the benefits of smoking cessation according to the age at quitting.

Design, Setting, and Participants

This population-based, retrospective cohort study included Korean participants aged 30 years and older who underwent 2 or more consecutive health examinations under the National Health Insurance Service since 2002 and were followed-up until 2019. Data analysis was performed from April to September 2023.

Exposures

Exposures included (1) time-updated smoking status based on biennial changes in smoking status, defined as complete quitters, transient quitters, relapsed quitters, continuous smokers, and never smokers; (2) duration of smoking cessation, defined as years since quitting; and (3) categorical variable for age at quitting.

Main Outcomes and Measures

The primary cancer was ascertained using the cancer registry data: all-site cancer (International Statistical Classification of Diseases and Related Health Problems, Tenth Revision [ICD-10] codes C00-43, C45-96, or D45-D47), lung cancer (ICD-10 code C34), liver cancer (ICD-10 code C22), stomach cancer (ICD-10 code C16), and colorectal cancer (ICD-10 codes C18-20). Hazard ratios (HRs) and 95% CIs were estimated using a Cox proportional hazards regression model with follow-up years as the timescale.

Results

Of the 2 974 820 participants, 1 727 340 (58.1%) were men (mean [SD] age, 43.1 [10.0] years), and 1 247 480 (41.9%) were women (mean [SD] age, 48.5 [9.9] years). Over a mean (SD) follow-up of 13.4 (0.1) years, 196 829 cancer cases were confirmed. Compared with continuous smokers, complete quitters had a lower risk of cancer, with HRs of 0.83 (95% CI, 0.80-0.86) for all cancer sites, 0.58 (95% CI, 0.53-0.62) for lung, 0.73 (95% CI, 0.64-0.82) for liver, 0.86 (95% CI, 0.79-0.93) for stomach, and 0.80 (95% CI, 0.72-0.89) for colorectum. The cancer risk exhibited a slightly higher value for 10 years after quitting compared with continued smoking and then it decreased over time, reaching 50% of the risk associated with continued smoking after 15 or more years. Lung cancer risk decreased 3 years earlier than that of other cancer types, with a larger relative reduction. Regardless of quitting age, a significant reduction in the cancer risk was observed. Quitting before the age of 50 years was associated with a greater reduction in lung cancer risk (HR, 0.43; 95% CI, 0.35-0.53) compared with quitting at age 50 years or later (HR, 0.61; 95% CI, 0.56-0.66).

Conclusions and Relevance

In this population-based retrospective cohort study, sustained smoking cessation was associated with significantly reduced risk of cancer after 10 years since quitting. Quitting at any age helped reduce the cancer risk, and especially for lung cancer, early cessation before middle age exhibited a substantial risk reduction.

Metabolic Differences between Ex-Smokers and Nonsmokers: A Metabolomic Analysis

The aim of this study was to compare changes in the metabolite levels of ex-smokers and nonsmokers using a metabolomics approach, accounting for the weight gain in ex-smokers. Volunteer ex-smokers and nonsmokers were recruited from two cohorts Shijingshan (174) and Xishan (78), respectively, at a 1 : 1 ratio for age and sex. Nontargeted metabolomics was performed on the volunteers' blood samples using liquid chromatography-mass spectrometry, and multivariate statistical analysis was performed using principal component analysis and orthogonal partial least squares discriminant analysis. Enrichment analysis was used to identify Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with differential metabolites and weighted gene co-expression network analysis and maximal correlation coefficient (MCC) algorithms were used to identify key metabolites. The results revealed no significant differences between the distribution of blood metabolite levels in the ex-smokers and nonsmokers. The biosynthesis of valine, leucine, and isoleucine was determined to be associated with differential metabolites, and five key metabolites were identified. Further analysis revealed differences in weight gain and regained metabolite levels in ex-smokers, and 10 differential metabolites were identified that may be associated with weight gain in ex-smokers. These findings suggest that quitting smoking restores metabolites to almost normal levels and results in weight gain. The identified key metabolites and metabolic pathways may also provide a basis for clinical studies.

Lifelong smoking status, weight gain, and subsequent risk of major adverse cardiovascular events: Long-term follow-up of a middle-aged Chinese population

OBJECTIVE

The aim of this study was to explore the association of lifelong smoking status with risk of major adverse cardiovascular events (MACE) accounting for weight change in a Chinese cohort.

METHODS

The cohort of the People's Republic of China-United States of America (PRC-USA) Collaborative Study of Cardiovascular and Cardiopulmonary Epidemiology was established in 1983 to 1984, resurveyed during 1987 to 1988 and 1993 to 1994, and followed up to 2005. A total of 5,849 participants who survived in 1993 to 1994 were classified into never smokers, long-term quitters, short-term quitters, short-term relapsers and new smokers, long-term relapsers and new smokers, and persistent smokers according to the information on lifelong smoking status collected in all three surveys. The associations of lifelong smoking status with MACE in the subsequent 10 years were explored with Cox proportional hazards models.

RESULTS

During a median follow-up of 10.2 years, 694 participants had MACE. Compared with persistent smokers, the multivariable-adjusted hazard ratio of developing MACE was 0.83 (95% CI: 0.61-1.12) for short-term quitters, 0.75 (95% CI: 0.54-1.02) for long-term quitters, and 0.68 (95% CI: 0.54-0.85) for never smokers (p_trend = 0.001). In comparison, the hazard ratio was 1.03 (95% CI: 0.77-1.35) for long-term relapsers and new smokers and 0.78 (95% CI: 0.46-1.22) for short-term relapsers and new smokers (p_trend = 0.018). These associations were not significantly altered by further adjusting for weight change in the past 10 years.

CONCLUSIONS

Lifelong smoking status is significantly associated with risk of MACE. As time duration increased, health benefit to quitters would become close to that of never smokers, and harms to relapsers and new smokers would become close to that of persistent smokers.

Smoking cessation-associated mortality reduction: A case-control study in Tianjin city, China

INTRODUCTION

Smoking-attributed mortality is increasing steadily in most developing countries. The aim of the study is to assess the reduction in smoking-associated mortality following cessation.

METHODS

Death data were collected from 2016 to 2017. Cases were deaths from pre-defined diseases of interest (65298); controls were deaths from pre-defined non-smoking-related diseases (13527). Case versus control odds ratios for ex-smokers versus smokers were calculated by age, sex, marital status and education with standardized logistic regression. These are described as mortality rate ratios (RRs, calculated as odds ratios), with a group-specific confidence interval (CI). The statistical analysis of the data was conducted from June to August 2019.

RESULTS

For deaths from pre-defined non-smoking-related diseases at age 35–59 years, the RRs for quitting smoking 0–4, 5–9 or ≥10 years ago and never smoking were 0.66 (95% CI: 0.55–0.78), 0.58 (95% CI: 0.38–0.88), 0.61 (95% CI: 0.45–0.82), and 0.43 (95% CI: 0.39–0.46), respectively. The same trend was found at ages 60–69 years and 70–79 years. Younger age of quitting (25–44 or 45–64 years) appeared to be associated with greater protection among the age groups: RR was 0.55 (95% CI: 0.42–0.74) and 0.67 (95% CI: 0.56–0.79), respectively, at age 35–59 years. Among the patients who died of lung cancer, the strong protective effect can only be observed when the duration of quitting is ≥10 years. The effect of smoking cessation on the risk of death from cardiovascular disease can be observed when the duration of quitting is 1–5 years.

CONCLUSIONS

Longer durations of smoking cessation are associated with progressively lower mortality rates from the diseases of interest, such as lung cancer and other smoking related cancers. For sustainable monitoring of tobacco-attributed mortality, smoking information over decades, such as smoking duration and quit smoking years, should be recorded during registration of death.

Predictors of long-term abstinence rate by income level in the Korean smoking cessation programme

BACKGROUND AND AIMS

To assess whether predictors of success in stopping smoking vary as a function of income level in Korean smoking cessation services.

DESIGN

Prospective study of predictors of smoking cessation up to 6 months' follow up.

PARTICIPANTS

A sample of 954 people (mean age 49.13 ± 10.69 years; 863 [90.5%] men) enrolled in the Korean National Health Insurance Service smoking cessation programme in 2015.

MEASURES

The outcome measure was self-reported continuous abstinence up to 6-month follow up. Predictors were income and other sociodemographic variables as well as smoking-related variables measured at baseline.

RESULTS

The continuous 6-month abstinence rate was 30.5%. The adjusted odds of 6-month continuous abstinence were lower among low-income versus the middle- or high-income smokers (OR, 0.54; 95% CI, 0.35-0.84), those with severe versus light/moderate cigarette dependence (OR, 0.72; 95% CI, 0.52-0.98), and use of bupropion versus varenicline (OR, 0.60; 95% CI, 0.39-0.91). The association between cigarette dependence and outcome was only present among low-income smokers.

CONCLUSIONS

Lower income, higher cigarette dependence, and choice of bupropion versus varenicline are associated with lower chances of stopping smoking in Korean smoking cessation services, but the association with cigarette dependence is only found in low-income smokers.