Michiyo Yamakawa

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.

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.

Intrauterine Exposure to Methylmercury and Neurocognitive Functions: Minamata Disease.

A large-scale food poisoning caused by methylmercury was identified in Minamata, Japan, in the 1950s. The severe intrauterine exposure cases are well known, although the possible impact of low-to-moderate methylmercury exposure in utero are rarely investigated. We examined neurocognitive functions among 22 participants in Minamata, mainly using an intelligence quotient test (Wechsler Adults Intelligent Scale III), in 2012/2013. The participants tended to score low on the Index score of processing speed (PS) relative to full-scale IQ, and discrepancies between PS and other scores within each participant were observed. The lower score on PS was due to deficits in digit symbol-coding and symbol search and was associated with methylmercury concentration in umbilical cords. The residents who experienced low-to-moderate methylmercury exposure including prenatal one in Minamata manifested deficits in their cognitive functions, processing speed in particular.

Breast-feeding and hospitalization for asthma in early childhood: a nationwide longitudinal survey in Japan

OBJECTIVE Whether or not breast-feeding is protective against asthma among children is still controversial. Therefore, we examined the effects of breast-feeding on hospitalization for asthma in early childhood. DESIGN Secondary data analyses of a nationwide longitudinal survey of children in Japan ongoing since 2001, with results collected from 2001 to 2004. We used logistic regression models to evaluate the associations of breast-feeding with hospitalization for asthma in children between the ages of 6 and 42 months, adjusting for childrens factors (sex, day-care attendance and presence of older siblings) and maternal factors (educational attainment and smoking habit). Setting All over Japan. SUBJECTS Term singleton children with information on feeding practices during infancy (n 43367). RESULTS After adjusting for maternal factors and childrens factors, exclusive breast-feeding at 6-7 months of age was associated with decreased risk of hospitalization for asthma in children. The adjusted odds ratio was 0.77 (95% CI 0.56, 1.06). One-month longer duration of breast-feeding was associated with a 4% decreased risk of hospitalization for asthma (OR = 0.96; 95% CI 0.92, 0.99). CONCLUSIONS The protective effects of breast-feeding on hospitalization for asthma were observed in children between the ages of 6 and 42 months.

Association of maternal age with child health: A Japanese longitudinal study

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 21st 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 <25 years, odds ratios of hospital admission at 18 months were 0.97 [95% CI: 0.86, 1.09], 0.92 [0.81, 1.05], 0.76 [0.65, 0.90], and 0.71 [0.51, 0.98] for mothers aged 25.0–29.9, 30.0–34.9, 35.0–39.9, and >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.

Diarrhea and related factors among passengers on world cruises departing from Japan

BACKGROUND Despite growth in the number of cruises worldwide, evidence about diarrhea experienced by cruise ship passengers remains sparse. We investigated rates of diarrhea and related factors among passengers on world cruises departing from Japan. METHODS Targeting passengers on five world cruises (n = 4180) from 2012 to 2013 (85-103 travel days), we calculated rates of health seeking behavior for diarrhea by sex, age group, and number of roommates for each cruise. We estimated rate ratios and 95% confidence intervals, using the group aged 20-39 years, women, and 2-4 roommates as referent categories. RESULTS We found 5.04-6.00 cases per 10,000 person-days in the five cruises, with an elevated number after calling at ports. Older passengers (>60 years) and passengers with fewer roommates had an elevated risk of health seeking behavior for diarrhea, although passengers aged <20 years had an elevated risk on one cruise. After controlling for covariates (including cruise), significant associations remained for passengers aged >60 years and without roommates. CONCLUSIONS Older passengers and passengers with fewer roommates may be more likely to seek medical treatment for diarrhea during travel on a world cruise, and should take preventive measures.

National data showed that delayed sleep in six-year-old children was associated with excessive use of electronic devices at 12 years

Cross‐sectional studies have shown associations between adolescent sleep problems and the use of electronic devices, such as mobile phones, but longitudinal studies remain scarce. We explored any association between delayed bedtimes at six years old and the excessive use of electronic devices at 12 years of age. Texting was a prime focus.

Maternal smoking location at home and hospitalization for respiratory tract infections among children in Japan

ABSTRACT We examined the effects of maternal smoking location at home on hospitalization for respiratory tract infections among young children in Japan. We used the large nationwide population-based longitudinal survey and restricted study participants to children born after 37 gestational weeks and singleton births (n = 43,851). We evaluated the associations among children between the ages of 6 and 18 months and between the ages of 18 and 30 months, respectively. After adjusting for potential confounders, both maternal outdoor and indoor smoking were associated with the elevated risk. The adjusted odds ratios (95% confidence intervals) of maternal outdoor and indoor smoking (vs nonsmoking mothers) were 1.21 (1.01–1.44) and 1.18 (1.04–1.33), respectively, in children between the ages of 6 and 18 months. We thus encourage a smoke-free home policy to protect children from second- and third-hand smoke exposure.