Shohei Yamamoto

Adult height may reflect early-life environmental conditions that influence the risk of type 2 diabetes mellitus (DM). While taller height has been linked to lower DM risk, evidence from East Asia remains limited and inconsistent. Given that DM in East Asians often occurs at lower BMI levels, population-specific research is needed. We examined the prospective association between adult height and incident DM in a large Japanese working population, focusing on differences by sex and birth cohort. Data were obtained from annual health checkups of 63,264 workers from 12 companies in Japan, comprising 54,188 men and 9076 women aged 20-64 years at baseline. Participants were classified by quartile of adult height for each sex. DM was defined as either when the participants had glycated hemoglobin (HbA1c) ≥ 6.5%, random glucose ≥ 200 mg/dL, fasting glucose ≥ 126 mg/dL, or when they were receiving antidiabetic treatment. Time ratios (TRs) and 95% confidence intervals (CIs) for the duration of remaining free from DM were estimated using a sex-stratified accelerated failure time model. We also examined whether the association varied by birth cohort, by comparing individuals born in 1960 or earlier with those born later. During a median follow-up period of 9.4 years, 5829 men and 448 women developed DM. For the highest vs. lowest height categories, after adjusting for age, body mass index, smoking, hypertension, and dyslipidemia, the TRs were 1.07 (95% CI, 1.02-1.13) in men and 0.98 (95% CI: 0.91-1.06) in women, respectively. When we stratified by birth cohorts, the height-DM association among men was more pronounced in the older cohort compared to the younger cohort. In a large cohort of Japanese workers, taller stature was associated with a prolonged duration of DM-free survival among men, particularly those in older cohorts. In women, however, the association between height and diabetes risk was inconclusive and warrants further investigation. The impact of stature on the risk of DM may be affected by sex and cohort effects, necessitating further research to disentangle these effects.

Although cross-sectional studies have shown that elevated serum manganese, cobalt, copper, zinc, selenium, and iodine are associated with a higher prevalence of type 2 diabetes, prospective evidence remains limited globally. This study aims to examine these associations in Japanese adults. A nested case-control study was performed in a cohort of 4754 health checkup examinees. During a 5-year follow-up, 325 cases of type 2 diabetes were identified by HbA_1c, plasma glucose, or self-report. For each case, two controls were randomly matched for sex, age, and checkup date, resulting in 611 controls with measurements of serum trace elements. Serum trace elements were measured using triple quadrupole inductively coupled plasma mass spectrometry. Conditional logistic regression analysis was used to estimate the odds ratio of type 2 diabetes across quartiles of serum trace elements while adjusting for potential confounders. Compared with participants in the lowest quartile of serum manganese, those in the highest quartile had higher odds of type 2 diabetes (odds ratio: 1.95; 95% CI: 1.11, 3.41). Comparison of the highest and the lowest quartiles showed that higher serum zinc levels, albeit not statistically significant, were associated with a higher odds ratio for type 2 diabetes (odds ratio: 1.49; 95% CI: 0.93, 2.41). No association was found between each of the other elements and type 2 diabetes. Although manganese and zinc play a key role in glucose metabolism, our findings suggest that excessive circulating levels of these elements are associated with an increased incidence of type 2 diabetes.

Background: While evidence from Western countries links low-to-moderate alcohol consumption to a lower risk of type 2 diabetes mellitus (T2D), findings have been inconsistent in Asia. Since T2D in Asia involves both insulin resistance and deficient insulin secretion, both of which are differently affected by alcohol, we prospectively examined whether the association differs according to body mass index (BMI) categories among the Japanese.Methods: Participants were 31,524 health checkup examinees (26,819 males and 4,705 females aged 20-64 years) who were free from diabetes at baseline. Self-reported data on alcohol use were used to estimate the average daily alcohol consumption at the baseline. Incident diabetes was identified at annual checkups during the follow-up period. A Cox proportional hazards model was used to estimate hazard ratios and 95% confidence intervals.Results: During a median follow-up of 12.0 years, 3,527 male and 287 female participants developed T2D. The association between alcohol consumption and T2D risk differed markedly by BMI in both sexes. Among males, low- and moderate-level alcohol consumption was associated with a lower T2D risk in individuals with BMI ≥25.0 kg/m2, whereas consumption at a level of 2 go/day (approximately 46 g ethanol) was linked to an increased T2D risk in those with BMI ≤22.0 kg/m2. In females, similar patterns were observed, although confidence intervals were broad due to smaller sample size.Conclusions: In Japan, low-to-moderate alcohol consumption may lower T2D risk in those with excess body weight, while high alcohol consumption may increase T2D risk in those with lower BMI.

Objective: This study aimed to investigate the association between work intervals and metabolic syndrome (MetS) among Japanese daytime workers. Methods: A cross-sectional analysis was conducted on 5094 daytime workers from the Japan Epidemiology Collaboration on Occupational Health Study. Work intervals, with and without commuting, were calculated using a self-administered questionnaire. The Joint Interim Statement criteria defined MetS. Logistic regression estimated odds ratio (OR) and 95% confidence interval (CI) for MetS across quartiles of work intervals. Results: Although participants with the shortest interval had unhealthy lifestyles, they had a lower prevalence of MetS (OR, 0.75; 95% CI, 0.59–0.97) than those with the longest. This association was no longer significant after accounting for commuting (OR, 0.86; 95% CI, 0.68–1.10). MetS was more prevalent among those with unhealthy lifestyles, regardless of work interval. Conclusions: Cross-sectionally measured shorter work intervals were not associated with a higher prevalence of MetS.

Background: The impact of the simultaneous circulation of COVID‐19 and seasonal influenza, termed the “Twindemic,” on absenteeism among healthcare workers (HCWs), particularly those with children, remains unclear. We aimed to investigate the associations of living with school‐aged children with the risk of SARS‐CoV‐2 and influenza infections and the risk of absenteeism due to own‐ or family‐related COVID‐19 or influenza events among HCWs during the Twindemic.Methods: This prospective study followed 1473 HCWs at a tertiary hospital in Tokyo from December 2023 to March 2024. We tracked the incidence of SARS‐CoV‐2 and influenza infections and absenteeism due to COVID‐19 or influenza‐related family events. We estimated the hazard ratios (HRs) or incidence rate ratios (IRRs) of these outcomes across living arrangements, focusing on cohabitation with school‐aged children.Findings: HCWs living with younger school‐aged children (≤ third grade of junior school) had a higher risk of SARS‐CoV‐2 and influenza infections, with HRs [95% confidence interval (CI)] of 1.90 [0.97–3.69] and 2.42 [1.04–5.66], respectively, compared with those living with cohabitants without school‐aged children. Additionally, they showed a higher IRR [95% CI] for absenteeism due to family‐related events (10.9 [4.88–24.5]), and their overall IRR [95% CI] of absenteeism due to own/family‐related events was 3.76 [2.59–5.46].Conclusion: The Twindemic has heightened absenteeism risks among HCWs with school‐aged children, emphasizing the need for targeted support to help HCWs manage both their professional duties and family responsibilities during such challenging times.

Background: After the prolonged coronavirus disease 2019 pandemic, during which the seasonal influenza epidemic was suppressed, Japan experienced a record-breaking influenza A/H1N1 outbreak in the 2024–2025 season. This situation also raises a concern about the immunogenicity of the annual inactivated influenza vaccine. This study evaluated postvaccination hemagglutination inhibition (HI) antibody titers and their association with influenza infection risk among healthcare workers. Methods: A serosurvey was conducted among staff at a national medical and research center in Tokyo in December 2024, 1 month after staff received the inactivated influenza vaccine. HI antibody titers against vaccine strains were measured, and participants were followed for influenza infection until January 2025. Seroprotection was defined as an HI titer ≥40. A Cox proportional hazards model assessed the association between HI titers and infection risk among vaccinated participants. Results: Among 1507 vaccinated participants, only 12.7% had seroprotective HI titers against A/H1N1. Around 90% had no influenza history for at least 4 seasons and had received repeated vaccinations over 2 seasons. Participants with HI titers <40 had a 4-fold higher infection risk than those with titers ≥40. A dose-response association was observed, even within the range below the titer of 40. Relative to titers <10, titers of 10 and 20 conferred 47.3% and 57.9% protection, respectively. Conclusions: After a prolonged period without a major influenza epidemic, HI titers against A/H1N1 were extremely low in vaccinated healthcare workers. Nonetheless, higher postvaccination HI titers, even at relatively low levels, were associated with protection, supporting the benefit of vaccines.

Background After the prolonged COVID–19 pandemic, during which the seasonal influenza epidemic was suppressed, Japan experienced a record–breaking influenza A/H1N1 outbreak in the 2024/2025 season. This situation also raises a concern about the immunogenicity of the annual quadrivalent inactivated influenza vaccine (QIIV). This study evaluated post-vaccination hemagglutination inhibition (HI) antibody titers and their association with influenza infection risk among healthcare workers. Methods A serosurvey was conducted among staff at a national medical and research center in Tokyo in December 2024, one month after staff received the QIIV. HI antibody titers against vaccine strains were measured, and participants were followed for influenza infection until January 2025. Seroprotection was defined as an HI titer ≥40. A Cox proportional hazards model assessed the association between HI titers and infection risk among vaccinated participants. Results Among 1,507 vaccinated participants, only 12.7% had seroprotective HI titers against A/H1N1. Around 90% had no influenza history for at least four seasons and had received repeated vaccinations over two seasons. Participants with HI titers Conclusions After a prolonged period without a major influenza epidemic, HI titers against A/H1N1 were extremely low in vaccinated healthcare workers. Nonetheless, higher post–vaccination HI titers, even at relatively low levels, were associated with protection, supporting the benefit of vaccines.

Objectives: This study examines the cross-sectional association between relatively lower-intensity physical activity (LIPA) during leisure time and presenteeism, accounting for relatively higher-intensity physical activity (HIPA) during leisure time. Methods: Data were derived from 11 438 workers from 6 worksites of large companies in Japan, which participated in a questionnaire survey conducted between fiscal years 2018 and 2020. Frequency and duration per occasion were assessed for leisure-time physical activities at 3 intensities as determined by shortness of breath. LIPA was defined as activity not causing shortness of breath. The participants were divided into 3 groups according to LIPA volume (none, <60 min/wk, or ≥60 min/wk) and into 2 groups according to HIPA volume (none or engaged). A single question assessed the participants’ presenteeism through self-ratings of their work performance. A multivariable Poisson regression model with a robust variance estimator estimated prevalence ratios (PRs) of presenteeism and their 95% CIs across the categories for both LIPA and HIPA. Results: The prevalence of presenteeism tended to decrease with increasing amounts of LIPA and HIPA (P for trend <.001). Among those who did not engage in HIPA, a significantly lower prevalence of presenteeism was observed among individuals who engaged in LIPA for ≥60 min/wk compared with those who did not (adjusted PR = 0.74; 95% CI = 0.68-0.81). Conclusions: This study supports the protective role of LIPA during leisure time that does not cause shortness of breath against presenteeism among workers who do not engage in HIPA during leisure time.

Background The COVID-19 pandemic and associated restrictions on human activities have greatly changed lifestyles, which might have deteriorated the cardiometabolic profile. Objective This study aimed to examine the effect of the COVID-19 pandemic on the incidence of cardiometabolic risk factors among Japanese workers in fiscal years (FY) 2020 and 2021 compared with the prepandemic period. Method This study comprised an average of 71 025 employees in Japan who underwent annual health check-ups for at least two successive years from 2015 to 2021. Annual incidence rates from 2016 to 2021 were assessed for obesity, diabetes, hypertension, dyslipidaemia and metabolic syndrome (MetS). The observed incidence rates in 2020 and 2021 were compared with the predicted incidence based on prepandemic trends (2016 to 2019). Results Relative to the prepandemic, the incidence of all the outcomes, except for dyslipidaemia, significantly increased in 2020. Between FY 2016 and 2019, the adjusted mean incidence of obesity, diabetes, hypertension, dyslipidaemia and MetS was 5.0%, 1.4%, 5.3%, 17.4% and 7.6%, respectively. In FY 2020, the adjusted incidence (95% CI) of these outcomes increased to 6.02 (5.80 to 6.24), 1.84 (1.73 to 1.96), 6.62 (6.40 to 6.83), 19.31 (18.83 to 19.78) and 8.51 (8.23 to 8.78), which were higher than the predicted incidence of 5.24 (4.99 to 5.49), 1.54 (1.41 to 1.67), 6.02 (5.76 to 6.27), 18.58 (18.00 to 19.16) and 8.05 (7.71 to 8.38) for 2020, respectively. The incidence returned to the prepandemic levels in FY 2021. Conclusion Results showed a worsening of the cardiometabolic profile during the initial year of the pandemic, which was reverted in the second year to the levels before the pandemic.