Background: Although many observational studies have demonstrated significant relationships between obesity and cardiometabolic traits, the causality of these relationships in East Asians remains to be elucidated.

Methods: We conducted individual-level Mendelian randomization (MR) analyses targeting 14,083 participants in the Japan Multi-Institutional Collaborative Cohort Study and two-sample MR analyses using summary statistics based on genome-wide association study data from 173,430 Japanese. Using 83 body mass index (BMI)-related loci, genetic risk scores (GRS) for BMI were calculated, and the effects of BMI on cardiometabolic traits were examined for individual-level MR analyses using the two-stage least squares estimator method. The β-coefficients and standard errors for the per-allele association of each single-nucleotide polymorphism as well as all outcomes, or odds ratios with 95% confidence intervals were calculated in the two-sample MR analyses.

Results: In individual-level MR analyses, the GRS of BMI was not significantly associated with any cardiometabolic traits. In two-sample MR analyses, higher BMI was associated with increased risks of higher blood pressure, triglycerides, and uric acid, as well as lower high-density-lipoprotein cholesterol and eGFR. The associations of BMI with type 2 diabetes in two-sample MR analyses were inconsistent using different methods, including the directions.

Conclusion: The results of this study suggest that, even among the Japanese, an East Asian population with low levels of obesity, higher BMI could be causally associated with the development of a variety of cardiometabolic traits. Causality in those associations should be clarified in future studies with larger populations, especially those of BMI with type 2 diabetes.

Background: The association between the frequency of going outdoors and the risk of poor oral health has been reported in several studies; however, the findings have been inconclusive.

Methods: We conducted a 3-year longitudinal study of 19,972 Japanese adults aged ≥65 years who reported no poor oral condition at baseline in 2013. The respondents rated their frequency of going outdoors in three categories (≤1, 2–3, or ≥4 times/week), and the oral conditions reported in 2016 included tooth loss, chewing difficulty, swallowing difficulty, dry mouth, and composite outcomes. The associations between the frequency of going outdoors and the risk of poor oral health were examined as relative risk ratios (RRs) and 95% confidence intervals (CIs) using multivariable Poisson regression, while mediation analysis was performed to investigate indirect effects.

Results: During the follow-up, 32.5% of participants developed poor oral health. In the mediation analysis, indirect effects were observed through low instrumental activities of daily living, depressive symptoms, little social network diversity, and underweight. Compared to going outdoors ≥4 times/week, the multivariable RRs of composite poor oral health conditions were 1.12 (95% CI, 1.05–1.20) for 2–3 times/week and 1.22 (95% CI, 1.07–1.39) for ≤1 time/week (P-trend < 0.001). Similar associations were observed for tooth loss, chewing difficulty, and swallowing difficulty; the corresponding RRs were 1.07 (95% CI, 0.97–1.19) and 1.36 (95% CI, 1.13–1.64) (P-trend = 0.002), 1.18 (95% CI, 1.06–1.32) and 1.30 (95% CI, 1.05–1.60) (P-trend < 0.001), and 1.15 (95% CI, 1.01–1.31) and 1.38 (95% CI, 1.08–1.77) (P-trend = 0.002), respectively.

Conclusion: The frequency of going outdoors was inversely associated with the risk of poor oral health through several modifiable risk factors in the older population.

Introduction: The burden of epilepsy is thought to be high but is difficult to measure. Very few studies in Japan have attempted to estimate prevalence and incidence rates of epilepsy in Japan.

Methods: This retrospective cohort study used commercially collected nationwide insurance claims data from a cohort of 10 million persons between 2012 and 2019 among those aged 0 to 74 years. Using the claims data, cases were identified, and incidence and prevalence rates were estimated.

Results: A total of 9,864,278 persons were included. The average age was 34.5 (standard deviation, 18.5) years. A total of 77,312 persons were diagnosed with epilepsy over the 8-year observation period, with a prevalence rate of 6.0 per 1,000 persons with almost no difference by gender. The highest rates were seen among those aged 70–74 years; prevalence rates tended to rise with calendar year (5.4/1,000 in 2012 and 6.0/1,000 in 2019). The incidence rate of epilepsy was 72.1 per 100,000 person-years with slightly higher rates seen among females. Incidence rates were highest at ages less than 12 months (199.8/100,000 person-years), followed by the eldest age group (70–74 years, 179.4/100,000 person-years).

Conclusion: Understanding the magnitude of disease burden is the basis of determining health policies. In this study, the prevalence and incidence of epilepsy in Japan was shown based on the analysis results of a large-scale general population insurance claims data covering all over Japan.

Background: We aimed to clarify whether differences in food group intake according to household income have changed over the last decade in Japanese people aged 20 years or older.

Methods: This cross-sectional study was based on the 2010, 2014, and 2018 National Health and Nutrition Surveys in Japan. Food intake was assessed using a 1-day semi-weighed household dietary record. The participants were categorized into three groups based on their income. The mean of each food intake according to the income group was estimated by adjusting for age, occupation, and number of participants from the same household. The significance of the interaction terms between income and survey year was evaluated to assess the change in income-related differences in food intake over time.

Results: Cereal intake was lower in the middle- and the highest-income groups than in the lowest-income group, regardless of sex, and the interaction between income and year was nonsignificant for cereal intake. In the former two surveys, vegetable intake was higher among the highest-income women, while in the 2018 survey, the vegetable intake decreased in the women in the middle- and the highest-income groups. The interaction between income and year was significant for vegetable intake among the women. For other foods, the differences in intake among the income groups did not significantly change over time.

Conclusion: The tendency for lower cereal intake in the higher-income groups was consistent over time in both the sexes, and the tendency for higher vegetable intake in the highest income women disappeared over time.

Background: Ambient particulate matter is classified as a human Class 1 carcinogen, and recent studies found a positive relationship between fine particulate matter (PM_2.5) and liver cancer. Nevertheless, little is known about which specific metal constituent contributes to the development of liver cancer.

Objective: To evaluate the association of long-term exposure to metal constituents in PM_2.5 with the risk of liver cancer using a Taiwanese cohort study.

Methods: A total of 13,511 Taiwanese participants were recruited from the REVEAL-HBV in 1991–1992. Participants’ long-term exposure to eight metal constituents (Ba, Cu, Mn, Sb, Zn, Pb, Ni, and Cd) in PM_2.5 was based on ambient measurement in 2002–2006 followed by a land-use regression model for spatial interpolation. We ascertained newly developed liver cancer (ie, hepatocellular carcinoma [HCC]) through data linkage with the Taiwan Cancer Registry and national health death certification in 1991–2014. A Cox proportional hazards model was utilized to assess the association between exposure to PM_2.5 metal component and HCC.

Results: We identified 322 newly developed HCC with a median follow-up of 23.1 years. Long-term exposure to PM_2.5 Cu was positively associated with a risk of liver cancer. The adjusted hazard ratio (HR) was 1.13 (95% confidence interval [CI], 1.02–1.25; P = 0.023) with one unit increment on Cu normalized by PM_2.5 mass concentration in the logarithmic scale. The PM_2.5 Cu-HCC association remained statistically significant with adjustment for co-exposures to other metal constituents in PM_2.5.

Conclusion: Our findings suggest PM_2.5 containing Cu may attribute to the association of PM_2.5 exposure with liver cancer.

Background: While tall stature has been linked to an increase in the risk of colorectal cancer (CRC), its association with cancer in the colorectum and its subsites remains unclear among Asians.

Methods: We conducted a pooled analysis of 10 population-based cohort studies among adults in Japan. Each study estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for CRC incidence associated with adult height were estimated using Cox proportional hazards regression with adjustment of the same set of covariates were then pooled to estimate summary HRs incidence using random-effect models.

Results: We identified 9,470 CRC incidences among 390,063 participants during 5,672,930 person-years of follow-up. Men and women with tall stature had a higher risk of CRC and colon cancer. HRs for CRC, colon cancer, and distal colon cancer for the highest versus lowest height categories were 1.23 (95% CI, 1.07–1.40), 1.22 (95% CI, 1.09–1.36), and 1.27 (95% CI, 1.08–1.49), respectively, in men and 1.21 (95% CI, 1.09–1.35), 1.23 (95% CI, 1.08–1.40), and 1.35 (95% CI, 1.003–1.81), respectively, in women. The association with proximal colon cancer and rectal cancer was less evident in both sexes.

Conclusion: This pooled analysis confirms the link between tall stature and a higher risk of CRC and colon cancer (especially distal colon) among the Japanese and adds evidence to support the use of adult height to identify those at a higher risk of CRC.