Sachiko Inoue

Long-term exposure to methylmercury and psychiatric symptoms in residents of Minamata, Japan

INTRODUCTION It is well-known that prenatal or postnatal exposure to methylmercury can produce neurological signs in adults and children, exemplified by a case of large-scale poisoning in Minamata, Japan, in the 1950s. However, evidence regarding whether pre- or postnatal exposure to methylmercury causes psychiatric symptoms (e.g., impairment of intelligence and mood and behavioral dysfunction) is still limited-excluding cases of fetal Minamata disease patients. METHODS We evaluated the effects of pre- or postnatal exposure to methylmercury on psychiatric symptoms using data derived from a 1971 population-based survey in Minamata and neighboring communities. We adopted residential areas as an exposure indicator and psychiatric symptoms as the outcome. Then, we estimated the adjusted prevalence odds ratio (POR) and confidence interval (CI) of psychiatric symptoms in relation to residential area. RESULTS There were 904 participants in Minamata (high exposure area), 1700 in Goshonoura (middle exposure area), and 913 in Ariake (low exposure area). Compared to the Ariake area, participants in the Minamata area manifested psychiatric symptoms more frequently: PORs for impairment of intelligence and mood and behavioral dysfunction were 5.2 (95% CI: 3.7-7.3) and 4.4 (95% CI: 2.9-6.7), respectively. Furthermore, participants with psychiatric symptoms in the Minamata area more frequently had neurological signs. Peaks in prevalence of psychiatric symptoms occurred around age 20 and in older age adults in the area. These findings did not change when we excluded those who had been officially certified as Minamata disease patients by that time. CONCLUSIONS The present study suggests a relationship between pre- or postnatal exposure to methylmercury and psychiatric symptoms among the general population in Minamata even after excluding officially certified patients.

Breastfeeding and Obesity Among Schoolchildren: A Nationwide Longitudinal Survey in Japan

IMPORTANCE Although it is suggested that breastfeeding is protective against obesity in children, the evidence remains inconclusive because of possible residual confounding by socioeconomic status or childrens lifestyle factors. Most of the participants in the previous studies were children in Western developed countries, so studies in a different context are awaited. OBJECTIVE To examine the associations of breastfeeding with overweight and obesity among schoolchildren in Japan, with adjustment for the potential confounders. DESIGN Secondary data analyses of a nationwide longitudinal survey ongoing since 2001, with results collected from 2001 to 2009. SETTING All over Japan. PARTICIPANTS A total of 43,367 singleton children who were born after 37 gestational weeks and had information on their feeding during infancy. EXPOSURES Five mutually exclusive infant feeding practice categories. MAIN OUTCOMES AND MEASURES Underweight, normal weight (referent group), overweight, and obesity at 7 and 8 years of age defined by using international cutoff points of body mass index by sex and age. RESULTS In multinomial logistic regression models with adjustment for childrens factors (sex, television viewing time, and computer game playing time) and maternal factors (educational attainment, smoking status, and working status), exclusive breastfeeding at 6 to 7 months of age was associated with decreased risk of overweight and obesity compared with formula feeding. The adjusted odds ratios were 0.85 (95% CI, 0.69-1.05) and 0.55 (95% CI, 0.39-0.78) for overweight and obesity, respectively, at 7 years of age. Similar results were observed at 8 years of age. CONCLUSIONS AND RELEVANCE Breastfeeding is associated with decreased risk of overweight and obesity among schoolchildren in Japan. Therefore, it would be better to encourage breastfeeding even in developed countries.

Social Cohesion and Mortality: A Survival Analysis of Older Adults in Japan

OBJECTIVES We examined the association between social cohesion and mortality in a sample of older adults in Japan. METHODS Data were derived from a cohort study of elderly individuals (65-84 years) in Shizuoka Prefecture; 14 001 participants were enrolled at baseline (1999) and followed up in 2002, 2006, and 2009. Among the 11 092 participants for whom we had complete data, 1427 had died during follow-up. We examined the association between social cohesion (assessed at both the community and individual levels) and subsequent mortality after control for baseline and time-varying covariates. We used clustered proportional hazard regression models to estimate hazard ratios (HRs) and confidence intervals (CIs). RESULTS After control for individual characteristics, individual perceptions of community cohesion were associated with a reduced risk of all-cause mortality (HR = 0.78; 95% CI = 0.73, 0.84) as well as mortality from cardiovascular disease (HR = 0.75; 95% CI = 0.67, 0.84), pulmonary disease (HR = 0.66; 95% CI = 0.58, 0.75), and all other causes (HR = 0.76; 95% CI = 0.66, 0.89). However, no statistically significant relationship was found between community cohesion and mortality risk. CONCLUSIONS Among the elderly in Japan, more positive individual perceptions of community cohesion are associated with reduced risks of all-cause and cause-specific mortality.

Association of breast feeding with early childhood dental caries: Japanese population-based study

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 childs 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.

Poor toddler-age sleep schedules predict school-age behavioral disorders in a longitudinal survey

OBJECTIVE Behavioral problems are often associated with poor sleep habits in children. We investigated whether undesirable toddler-age sleep schedules may be related to school-age behavioral problems. METHODS We analyzed the data of a nationwide longitudinal survey with available results from 2001 to 2011. The participants were 41,890 children. The predictors were waking time and bedtime at 2years of age, and the outcomes were assessed by determining the presence or absence of three attention problems and four aggressiveness problems at 8years of age. In logistic regression models with adjustments for confounding factors, we estimated odds ratios (ORs) and confidence intervals (CIs) for the association between toddler sleep schedules and behavior during primary-school age years. RESULTS The outcomes of attention problems and aggressiveness problems were observed in 1.7% and 1.2% of children, respectively, at 8years of age. The OR of an irregular or late morning waking time at 2years of age with the outcome of aggressiveness problems was 1.52 (95% CI, 1.04-2.22) in comparison to an early waking time. The OR of an irregular or late bedtime with attention problems was 1.62 (95% CI, 1.12-2.36), and the OR of an irregular or late bedtime with aggressiveness problems was 1.81 (95% CI, 1.19-2.77) in comparison to an early bedtime. CONCLUSION Poor toddler-age sleep schedules were found to predict behavioral problems during primary-school age years. Thus, good and regular sleep habits appear to be important for young childrens healthy development.

Breastfeeding and behavioral development: a nationwide longitudinal survey in Japan.

OBJECTIVE To prospectively examine the prolonged effect of breastfeeding on behavioral development. STUDY DESIGN We used a large, nationwide Japanese population-based longitudinal survey that began in 2001. We restricted participants to term singletons with birth weight >2500 g (n = 41 188). Infant feeding practice was queried at age 6-7 months. Responses to survey questions about age-appropriate behaviors at age 2.5 and 5.5 years were used as indicators of behavioral development. We conducted logistic regression analyses, controlling for potential child and parental confounding factors, with formula feeding as the reference group. RESULTS We observed a dose-response relationship between breastfeeding status and an inability to perform age-appropriate behaviors at both ages. With a single exception, all ORs for outcomes for exclusive breastfeeding were smaller than those for partial feeding of various durations. The protective associations did not change after adjustment for an extensive list of confounders or in the sensitivity analyses. CONCLUSION We observed prolonged protective effects of breastfeeding on developmental behavior skills surveyed at age 2.5 and 5.5 years. Beneficial effects were most likely in children who were breastfed exclusively, but whether a biological ingredient in breast milk or extensive interactions through breastfeeding, or both, is beneficial is unclear.

Critical appraisal of the 1977 diagnostic criteria for Minamata disease.

ABSTRACT Large-scale food poisoning caused by methylmercury was identified in Minamata, Japan, in the 1950s (Minamata disease). Although the diagnostic criteria for the disease remain current, few studies have been carried out to assess the diagnostic accuracy of the criteria. From a 1971 population-based investigation, data from 2 villages were selected: Minamata (high-exposure area; n = 779) and Ariake (low-exposure area; n = 755). The authors examined the prevalence of neurologic signs characteristic of methylmercury poisoning and the validity of the criteria. A substantial number of residents in the exposed area exhibited neurologic signs even after excluding officially certified patients. Using paresthesia of the extremities as the gold standard of diagnosis, the criteria had a sensitivity of 66%. The current diagnostic criteria as well as the official certification system substantially underestimate the incidence of Minamata disease.

Trends of preterm birth and low birth weight in Japan: a one hospital-based study

BackgroundThe proportions of preterm birth (PTB, ie., delivered before 37 gestational weeks) and low birth weight (LBW, ie., birth weight less than 2500 g at delivery) have been rising in developed countries. We sought to examine the factors contributing to the rise in Japan, with particular focus on the effects of obstetric interventions.MethodsWe used a database maintained by one large regional hospital in Shizuoka, Japan. We restricted the analysis to mothers who delivered live singleton births from 1997 to 2010 (n = 19,221). We assessed the temporal trends in PTB and LBW, then divided the study period into four intervals and compared the proportions of PTB and LBW. We also compared the newborns’ outcomes between the intervals.ResultsPTB, in particular medically indicated PTB, increased considerably. The increase was largely explained by changes in caesarean sections. The neonatal outcomes did not worsen, and instead the Apgar scores and proportions requiring neonatal intensive care unit (NICU) admission improved. In particular, the risks of NICU admission in the interval from 2007 to 2010 were decreased among all births [odds ratio (OR): 0.84; 95% confidence interval (CI): 0.75, 0.95] and medically indicated births (OR: 0.44; 95% CI: 0.29, 0.68) compared with the interval from 1997 to 2000.ConclusionsDespite the increases in PTB as well as LBW, the present study suggests benefits of obstetric interventions. Rather than simple categorization of PTB or LBW, indicators such as perinatal mortality or other outcomes may be more appropriate for evaluation of perinatal health in developed countries.

Association of Birth Length and Risk of Hospitalisation among Full-term Babies in Japan

BACKGROUND Barkers fetal programming hypothesis suggests that disproportionate size at birth may have a lifelong impact on ones health. However, the literature on birth length is considerably more sparse compared with birthweight. We, therefore, examined the relationship between birth length and hospitalisation early in life among Japanese children. METHODS We used the nationwide Longitudinal Survey of Babies in 21st Century and restricted the study subjects to full-term singleton babies (n = 44,057). We estimated the effects of birth length and birthweight on the risk of hospitalisation using log linear regression models. We controlled for a set of neonatal and maternal factors. RESULTS Birth length was associated with the chance of hospitalisation due to all causes between 6 and 18 months of age. In addition, the association was stronger than that with birthweight. Adjusted risk ratios showed that the relationship between birth length and hospitalisation was U-shaped: 1.16 [95% confidence intervals, 1.08, 1.25] at 30-48 cm, 1 [Reference] at 49 cm, 1.13 [1.04, 1.22] at 50 cm, and 1.11 [1.02, 1.20] at 51-60 cm. Short babies with low or high weight, as well as long babies with low weight, seem to be at increased risk of hospitalisation. CONCLUSIONS We found a U-shaped relationship between birth length and risk of hospitalisation due to all causes during the period from 6 to 18 months.

Who is at Risk of Inadequate Weight Gain During Pregnancy? Analysis by Occupational Status Among 15,020 Deliveries in a Regional Hospital in Japan

A lower bodyweight may be associated with adverse birth outcomes, such as low birth weight and being small for a given gestational age. In Japan, the rate of low birth weight has been increasing over the last two decades, such that both low pre-pregnancy weight and inadequate weight gain during pregnancy are viewed as critical issues in terms of the reproductive health of Japanese women. The aim of our study was to evaluate the relationship between socioeconomic status (SES) and inadequate weight gain during pregnancy. A cross-sectional, hospital-based study using data from a large hospital in Hamamatsu city, Japan, from 1997 to 2010 was conducted. Among a total of 21,855 deliveries, 15,020 participants were analyzed. Odds ratios and confidence intervals were estimated using a logistic regression model. We defined maternal occupational status as follows: home-maker married to a salaried-spouse, home-maker married to a self-employed spouse, home-maker married to a professional, all other home-makers, office worker, professional, and all other occupations. In the high SES groups (home-makers married to self-employed spouse and professional spouse, as well as office workers and professional workers), we found an association with inadequate weight gain during pregnancy, especially among underweight women. There was no association between SES and inadequate weight gain among normal-weight and overweight women. Japanese women from higher socioeconomic backgrounds appear to be at greater risk for inadequate weight gain. This result may contribute to enhancing prenatal education on pregnancy-related weight gain in Japan.