Climate change leads to adverse health effects globally, including increased heat-related mortality of the elderly. Besides physiological factors of aging and comorbidities, social isolation is one risk factor associated with adverse health effects of heat. In 2025, the Working Group Environmental Health at Hokkaido University and the Institute of General Practice from University of Cologne held a research workshop to explore joint solutions for climate-resilience in super-aged nations like Germany and Japan. The three-day interactive workshop was held at Hokkaido University, Sapporo, Japan and included a hybrid symposium with external experts as well as intensive exchange between the research groups. Jointly addressing social isolation and heat health risks, was identified as a promising way to increase health systems resilience in times of societal and environmental crisis, especially in super-aged countries. This commentary narratively summarizes the current evidence on interventions targeting social isolation and heat health risks, finding that current interventions aim to protect socially isolated older adults during heat waves, but do not intend to alleviate both, social isolation and heat health risks at a broader scale. Based on the discussions in the workshop this commentary proposes future research opportunities, entailing family-based as well as community-based approaches, which foster social connection throughout the year and are particularly triggered during hot days and heat waves. Further research is needed to co-develop and evaluate such interventions with older adults and their families and communities to increase resilience of societies and health systems.

Background: Publicly available aggregate health data can support regional surveillance of cardiometabolic risk, but analyses must address aggregation, ecological inference, and cell suppression or unavailability. Waist circumference and body mass index (BMI) capture related but distinct aspects of adiposity. We evaluated the usefulness and limitations of selected 10th National Database (NDB) Open Data indicators for prefecture-level cardiometabolic surveillance among Specific Health Checkup examinees in Japan.

Methods: We conducted an ecological descriptive analysis of the 10th NDB Open Data. Data were analyzed by prefecture, sex, and 5-year age band among examinees aged 40–74 years. Primary indicators were the percentage meeting the waist circumference criterion (≥85 cm in men, ≥90 cm in women) and the percentage with hemoglobin A1c (HbA1c) ≥6.5%; BMI categories were examined as exploratory indicators. Prefecture-level percentages were internally age-standardized within sex using the age distribution of publicly displayed examinee counts pooled across prefectures for each indicator as the internal standard. Cells displayed as “-” were treated as suppressed/unavailable and not as zero values.

Results: Waist circumference criterion data were complete across prefectures, sexes, and age bands. HbA1c ≥6.5% data were complete among men but included suppressed/unavailable cells among women, and BMI indicators had substantial cell suppression/unavailability. The age-standardized percentage meeting the waist circumference criterion ranged from 45.5% in Niigata to 60.6% in Okinawa among men and from 13.7% in Kyoto to 24.0% in Okinawa among women. HbA1c ≥6.5% ranged from 8.3% in Nagano to 11.3% in Miyagi among men and from 3.9% in Kanagawa to 7.8% in Saga among women. Okinawa had the highest percentage meeting the waist circumference criterion in both sexes. Waist-HbA1c correlations were positive in available-cell analyses, but estimates among women and estimates involving BMI were sensitive to cell availability and the prefectures included in the analysis.

Conclusions: The percentage meeting the waist circumference criterion was the most complete and robust descriptive indicator for prefecture-level cardiometabolic surveillance using the 10th NDB Open Data. HbA1c analyses among women and BMI-based analyses require suppression-aware interpretation. Ecological correlations should be interpreted as descriptive co-patterning of aggregate surveillance indicators, not as individual-level associations or evidence of regional determinants.

Trial registration: Not applicable.

Background: Reproductive history can be conceptualized as a life-course exposure integrating biological and social factors. Although reproductive factors have been associated with stroke risk and cognitive function, their relationships with structural brain changes remain unclear. Evidence from general population–based studies linking reproductive factors to brain volume, an intermediate marker of cognitive decline, is limited. This study examined whether age at menarche, age at menopause, estrogen exposure duration, and parity are associated with brain volume in postmenopausal women.

Methods: This cross-sectional study included 361 postmenopausal women aged ≥55 years from the Ohasama Study in Japan. Reproductive factors were obtained from a 1998 questionnaire were categorized into quartiles, and MRI data from 2009 to 2019 were analyzed with voxel-based morphometry. Associations were assessed using analysis of covariance adjusted for intracranial volume, age, birth cohort, and BMI. Effect sizes were reported as percent change and standardized effect sizes, with the smallest effect size of interest (SESOI) based on one-year age-related brain volume change.

Results: After covariate adjustment, most associations between reproductive factors and brain volume were attenuated. Earlier age at menarche showed a weak trend toward larger temporal lobe volume (β = 0.59 cm³, 95% CI −0.03 to 1.21; p = 0.06), corresponding to a 0.63% change and 0.06 SD, which was comparable to the SESOI (±0.54% or 0.06 SD). Earlier age at menopause was associated with smaller occipital lobe volume (β = −0.52 cm³, 95% CI −1.01 to −0.03; p = 0.04), corresponding to a −1.08% change and 0.10 SD, exceeding the primary SESOI threshold (±0.64% or 0.06 SD), although confidence intervals included effects smaller than the SESOI. No significant associations were found for estrogen exposure or parity.

Conclusion: Reproductive factors were not associated with moderate or large differences in brain volume in postmenopausal women. The slight, region-specific differences observed were comparable in magnitude to short-term age-related changes. These findings suggest that the clinical significance at the individual level is likely limited. However, subtle associations at the population level cannot be entirely excluded.

Background: Heatstroke is a major public health problem during summer, and meteorological conditions, particularly wet bulb globe temperature (WBGT), strongly influence its occurrence. However, even under similar heat conditions, heatstroke risk may vary according to behavioural patterns on weekdays, weekends/holidays, and post-holiday days. This study aimed to examine whether heatstroke-related ambulance transports in Tokyo vary according to day type after adjusting for WBGT.

Methods: We conducted a time-series analysis using daily heatstroke-related ambulance transports in Tokyo, Japan, during the warm season (May–September) from 2015 to 2025. The days were classified as weekday, weekend/holiday, or post-holiday. The WBGT data for seven locations in Tokyo were used, and the highest daily maximum WBGT served as the heat exposure indicator. Modified Poisson regression models were used to estimate risk ratios (RRs) and 95% confidence intervals (CIs) according to day type, adjusting for the WBGT category at lags 0 and 1 and the calendar year. The same models were applied by age group, severity, and place of occurrence. Four sensitivity analyses, including the use of alternative heat exposure indicators and exclusion of the coronavirus disease 2019 period, were conducted.

Results: After adjusting for WBGT and calendar year, the occurrence of heatstroke-related ambulance transports differed according to day type. Overall, ambulance transports tended to be more frequent on post-holiday days than on weekdays (RR, 1.08; 95% CI, 0.97–1.22). Among adults aged ≥65 years, transports were more frequent on post-holiday days (RR, 1.13; 95% CI, 1.00–1.28) and less frequent on weekends/holidays (RR, 0.87; 95% CI, 0.79–0.96). Among individuals aged <18 years, transports were markedly more frequent on weekends/holidays (RR, 1.80; 95% CI, 1.61–2.03). Weekend/holiday increases were also observed in mild cases and in public indoor and outdoor spaces and educational institutions, whereas cases in residences and workplaces were less frequent. Sensitivity analyses yielded similar results.

Conclusions: Heatstroke-related ambulance transports in Tokyo varied according to day type even after adjusting for WBGT, with distinct patterns across age groups, severity categories, and places of occurrence. Weekly behavioural patterns may contribute to heatstroke risk and warrant consideration in preventive strategies.

Background: Long-term birth cohort studies depend on sustained participant engagement. In such studies, children are not only observed over time but also increasingly become participants who experience, interpret, and evaluate their own involvement in research. However, research on continued participation has focused mainly on parental perspectives, with limited attention to children’s own views or to similarities and differences between parents and children. Against the growing recognition that people in medical research should be understood as participants rather than passive subjects, this study examined research participation experiences and retention intentions in both parents and children within a Japanese birth cohort.

Methods: We conducted a questionnaire survey from September to October 2024 within the Japan Environment and Children’s Study (JECS). The primary outcome was retention intention. Factors associated with retention intention were analyzed separately for parents and children using ordinal logistic regression. Parent-child concordance in retention intention was assessed descriptively using weighted Cohen’s kappa.

Results: Among 1,008 eligible parents of fifth-grade children, 485 responded (response rate, 44%). A large majority of parents (92%) and children (79%) reported willingness to continue participation. Parent–child responses showed moderate agreement (κ = 0.46). In separate adjusted ordinal logistic regression models, stronger parental retention intention was associated with lower perceived questionnaire burden (adjusted odds ratio [aOR]: 5.58, 95% confidence interval [CI]: 3.40–9.17), fewer concerns about possible disagreement with their child (aOR: 5.75, 95% CI: 3.51–9.42), and less difficulty scheduling study activities (aOR: 5.80, 95% CI: 3.50–9.63). In children, stronger retention intention was associated with anticipated gifts (aOR: 7.38, 95% CI: 2.93–18.56), talking with friends about the study (aOR: 6.02, 95% CI: 2.25–16.09), and a desire for peer interaction (aOR: 6.72, 95% CI: 3.39–13.29).

Conclusions: Parents and children both showed generally positive retention intentions, but disagreement was not negligible. Their retention intentions were associated with different participation-related experiences, suggesting that long-term birth cohort studies should attend to participants’ perspectives in age-specific ways. Understanding research participation through both parental and child experiences may help inform more participant-centered engagement strategies and support the quality of long-term cohort research.