Journal of Epidemiology Original Article J Epidemiol 2021;31(6):369-377 Widening Socioeconomic Inequalities in Smoking in Japan, 2001–2016 Hirokazu Tanaka1,2, Johan P. Mackenbach1, and Yasuki Kobayashi2 1Department of Public Health, Erasmus University Medical Center, Rotterdam, The Netherlands 2Department of Public Health, Graduate School of Medicine, the University of Tokyo, Tokyo, Japan Received January 29, 2020; accepted June 12, 2020; released online June 27, 2020 ABSTRACT Background: Japan is one of the world’s largest tobacco epidemic countries but few studies have focused on socioeconomic inequalities. We aimed to examine whether socioeconomic inequalities in smoking have reduced in Japan in recent times. Methods: We analyzed data from the Comprehensive Survey of Living Conditions, a large nationally representative survey conducted every 3 years (n ≈ 700,000 per year) in Japan, during 2001–2016. Age-standardized smoking prevalence was computed based on occupational class and educational level. We calculated smoking prevalence difference (PD) and ratio (PR) of (a) manual workers versus upper non-manual workers and (b) low versus high educational level. The slope index of inequality (SII) and relative index inequality (RII) by educational level were used as inequality measures. Results: Overall smoking prevalence (25–64 years) decreased from 56.0% to 38.4% among men and from 17.0% to 13.0% among women during 2001–2016. The PD between manual and upper non-manual workers (25–64 years) increased from 11.9% (95% confidence interval [CI], 11.0–12.9%) to 14.6% (95% CI, 13.5–15.6%) during 2001–2016. In 2016, smoking prevalence (25–64 years) for low, middle, and highly educated individuals were 57.8%, 43.9%, and 27.8% for men, and 34.7%, 15.9%, and 5.6% for women, respectively. SII and RII by educational level increased among both sexes. Larger socioeconomic differences in smoking prevalence were observed in younger generations, which suggests that socioeconomic inequalities in smoking evolve in a cohort pattern. Conclusions: Socioeconomic inequalities in smoking widened between 2001 and 2016 in Japan, which indicates that health inequalities will continue to exist in near future. Key words: epidemiology; smoking; socioeconomic factors; Japan; trends Copyright © 2020 Hirokazu Tanaka et al. This is an open access article distributed under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. control policies, the tobacco epidemic is still an ongoing issue in INTRODUCTION Japan, and requires focused measures for a smoke-free society. Japan is the fourth largest tobacco-consuming country in the Socioeconomic inequalities in smoking are a key causal world. In 2010, the cigarette consumption in Japan was 1,904 element of health inequalities.6 Socioeconomic inequalities in cigarettes per person-year.1 Currently, preventing smoking- smoking persist in high-income countries, such as the United related diseases is an important public health concern because States, European countries, and South Korea.7–10 However, there tobacco smoking remains a leading cause of death, especially is limited information regarding smoking prevalence by socio- among men.2 However, tobacco control in Japan has been economic status in Japan due to lack of (1) a nation-wide evaluated to be insufficient in comparison to the World Health surveillance system, (2) comprehensive evaluation of health Organization (WHO) Framework Convention on Tobacco behaviors, and (3) health policy for inequality reduction.11 Some Control.3 Looking back to the long-term trends in the last half Japanese studies revealed that income and occupation were of the century, smoking prevalence decreased incredibly from clearly associated with the differences in smoking prevalence in 83.7% in 1966 to 29.7% in 2016 among men aged 20 years and different socioeconomic groups during the 2000s.12,13 Regarding over.4 However, smoking prevalence in Japan is higher than those educational inequalities, Tabuchi and Kondo reported that larger of other high-income countries, such as the United States and inequalities in smoking were found among young men and several European countries.5 On the other hand, smoking women in terms of both relative and absolute measures in 2010.14 prevalence among women in Japan is lower than in other high- However, we found no studies that addressed trends in income countries,5 while the decline of smoking prevalence socioeconomic inequalities in smoking in Japan. among Japanese women has stagnated in recent years (see Within this context, the aim of the present study is to examine eFigure 1).4 Considering recent statistics on insufficient tobacco the trends in smoking prevalence by socioeconomic status using a Address for correspondence. Yasuki Kobayashi, Department of Public Health, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan (e-mail: [email protected]). DOI https://doi.org/10.2188/jea.JE20200025 HOMEPAGE http://jeaweb.jp/english/journal/index.html 369 Socioeconomic Inequalities in Smoking in Japan large nation-wide survey. We also assessed whether socio- unknown categories were also identified according to partic- economic inequalities in smoking reduced in Japan with attention ipants’ responses. Educational level was classified into three to a specific birth cohort. categories: “low” (defined as International Standard Classification of Education [ISCED]: 1–2), “middle” (ISCED: 3–4), and “high” (ISCED: 5–6). In Japan, “low” corresponds to elementary school= METHODS junior high school graduates, “middle” corresponds to high Data sources school graduates and technical professional school graduates, and We analyzed data from the Comprehensive Survey of Living Con- “high” corresponds to 2-year college, university, and graduate ditions (CSLC) conducted every 3 years from 2001 to 2016 (n ≈ school.19 The detailed classifications are presented in eTable 2 700,000 per year) in Japan, a large-scale national population-based and eTable 3. eTable 4 shows the distributions of educational survey by the Ministry of Health, Labour and Welfare (MHLW).15 level by occupational class estimated in the dataset. Micro data was extracted and used with permission from MHLW. The CSLC was launched in 1986, and it has been conducted every Analysis year to collect nation-wide data about living conditions, such as The analyses were restricted to men and women aged 25–64 years family make-up, occupation, and income. The health status survey, old with regard to occupational class because retirement is common an additional part of CSLC, has been conducted every 3 years from around the early 60s in Japan. As for educational level, we divided 1986, but the smoking status survey has been conducted only since the sample into two age groups: 25–64 and 65–94 years old. We 2001. According to MHLW, smoking prevalence (20 years and excluded survey participants aged 20–24 years old because this over) estimated by the CSLC were 48.4% for men and 14.0% for age band includes university and other higher education students. women in 2001, and 31.1% for men and 9.5% for women in 2016, All analyses were conducted using weighted samples by sex. The respectively.15 This prevalence was similar to both the Japan weighting scores provided by MHLW were recalibrated to obtain Tobacco Inc. Japan Smoking Rate Survey (29.7% for men and 9.7% average weight for all study participants equal to one, which resulted for women)4 in 2016 and the National Health and Nutrition Survey in the standard errors being approximated to those of the unweighted (30.2% for men and 8.2% for women) in 2016.16 sample when calculating age-standardized smoking prevalence. Regarding the survey of 2016, the household questionnaire and First, we calculated crude smoking prevalence by occupational health questionnaire covered whole households that were class, educational level, sex, and 5-year age groups (20–94 years randomly sampled in 5,530 districts out of 1,040,000 districts old) to assess age-specific smoking prevalence. Birth cohort- (approximately 50 households in each district) defined in the 2015 specific smoking prevalence differences between manual workers National Census. Household questionnaire includes demographics and upper non-manual workers were calculated to assess changes (sex, age, marital status, family make-up, health insurance, pen- within the birth cohort between 2001 and 2016. sion, child rearing, working status, occupation, and educational Second, age-standardized smoking prevalence by occupational background) whereas health questionnaire includes health status class and educational level was computed using the data in 5-year and medical help seeking behavior (subjective symptoms, regular age intervals. The 2013 European standard population was used visits to hospital=clinics, difficulties in daily life, self-assessed as reference for direct standardization because (1) the distribution health status, mental health, health checkup, alcohol consumption, is similar to what was observed in the 2000 Japanese Census (see and smoking status). The sampling method is under consideration eFigure 2); (2) the 1985 Japanese standard population, which is for improvement17; however, the CSLC is one of the most generally used for standardization for official Japanese statistics, important survey in Japan. eTable 1 shows the survey partic- deviates from the recent Japanese population