Objectives We investigated the association between breastfeeding duration during the first half year of life and the risk of early childhood caries from the age of 30 to 66 months in Japan. Design Observational study of a longitudinal survey. Setting A secondary data analysis of the Japanese Longitudinal Survey of Babies in the 21st Century. Participants 43 383 infants at the age of 6 months. Outcome measures Early childhood caries—defined as a child's visit to a dentist for treatment of dental caries during the past 12 months—was ascertained from the caregiver from the age of 30 months in the survey. We estimated the risk of dental caries each year according to duration of breast feeding using logistic regression analyses. We controlled for a set of biological factors (birth weight, sex, parity and maternal age at delivery) and socioeconomic factors (maternal educational attainment and smoking status, marital status at delivery, family income and region of birth and residence). Results We found that infants who had been breast fed for at least 6 or 7 months, both exclusively and partially, were at elevated risk of dental caries at the age of 30 months compared with those who had been exclusively formula fed. Adjusted ORs were 1.78 (95% CI, (1.45 to 2.17)) for the exclusively breastfed group and 1.39 (1.14 to 1.70) for the partially breastfed group. However, the associations became attenuated through the follow-up period and were no longer statistically significant beyond the age of 42 months for the partially breastfed group and beyond the age of 54 months for the exclusively breastfed group. Conclusions We found an association between breast feeding for at least 6 or 7 months and elevated risk of dental caries at age 30 months. However, the association became attenuated as children grew older.

Average maternal age at birth has been rising steadily in Western and some Asian countries. Older maternal age has been associated with adverse pregnancy and birth outcomes; however, studies on the relationship between maternal age and young children’s health remain scarce. Therefore, we sought to investigate the association of maternal age with child health outcomes in the Japanese population. We analyzed data from two birth cohorts of the nationwide Japanese Longitudinal Survey of Babies in 21^st Century (n₂₀₀₁ = 47,715 and n₂₀₁₀ = 38,554). We estimated risks of unintentional injuries and hospital admissions at 18 and 66 months according to maternal age, controlling for the following potential confounders: parental education; maternal parity, smoking status, and employment status; household income; paternal age, and sex of the child. We also included the following as potential mediators: preterm births and birthweight. We observed a decreasing trend in the risks of children’s unintentional injuries and hospital admissions at 18 months according to maternal age in both cohorts. In the 2001 cohort, compared to mothers 40.0 years, respectively, controlling for confounders. Our findings were in line with previous findings from population-based studies conducted in the United Kingdom and Canada suggesting that older maternal age may be beneficial for early child health.

Inoue S, et al. J Korean Med Sci. 2016 Mar;31(3):353-359. http://dx.doi.org/10.3346/jkms.2016.31.3.353

Assisted reproductive technology (ART) treatment accounted for 6% of total births in 2017 and is increasing which places Japan among the top worldwide in number of treatments performed. Although ART treatment patients often experience heavy physical and psychological burden, few epidemiologic studies have been conducted in Japan. We examined mental health and health-related quality of life (QOL) among women at early stages of treatment. We recruited 513 women who have initiated ART treatment, either in-vitro fertilization or intracytoplasmic sperm injection, from four medical facilities in the Tokyo area and through web-based approaches. At baseline, we collected socio-demographic information and assessed depressive symptoms, anxiety, and QOL. Descriptive analyses were performed overall and stratified by factors such as age. Mild depressive symptoms or worse, assessed with Quick Inventory of Depressive Symptoms, were observed among 54% of participants. Mean score for State-Trait Anxiety Inventory was 52 with a standard deviation of 11 for the state, and 39% were categorized as high anxiety. QOL results, assessed with SF-12, showed the same negative tendency for social functioning and role (emotional), while general health and physical functioning were consistent with the national average. Young participants appeared to suffer mentally more than older participants (p < 0.01 for depressive symptoms). Our findings suggest that patients may be at high risk of depressive symptoms, high anxiety, and low QOL even from the early stages of ART treatment.

Although Japan has entered a phase of population decline due to decades of low fertility, studies on the determinants of fertility choices among Japanese couples remain sparse. Previous studies, mostly conducted in Europe, suggest that men’s active involvement in household labour may promote childbearing. We tested whether men’s participation in childcare and housework has an influence on parity progression in Japan. Our results show a positive relationship between men’s participation in childcare and parity progression but no consistent relationship between men’s participation in housework and parity progression. We also observed that other factors such as the sex composition of existing children influences couples’ decision to have another child. Our findings add to the scarce literature on Japanese people’s fertility behaviour.