Short sleep duration at night in 2.5-year-old children is associated with childhood obesity at age 5.5 years: The Japanese children cohort study.

BACKGROUND: Obesity in children contributes to higher risks of various chronic diseases in adulthood and the prevalence has increased worldwide including Japan. OBJECTIVES: This study aims to examine the association between sleep duration at night in children aged 2.5 years and the subsequent risk of obesity at age 5.5 years. METHODS: This study is embedded in the Longitudinal Survey on Babies Born in the 21st Century, which recruited families who had a child born in Japan in 2001. The multivariable logistic regression models were applied to calculate odds ratios (OR) and 95 % confidence intervals (CI) of childhood obesity at 5.5 years, defined as percentage of overweight (POW) ≥ 20 % and body mass index (BMI) ≥ 95th percentile of this study population according to sleep duration at night collected at 2.5 years child age. RESULTS: Among 25,378 children, 2.6 % and 3.7 % were obese at age 5.5 years defined by POW and BMI respectively. Compared with night sleep duration > 11 h/d, shorter sleep durations in 2.5 years-old children were associated with higher risk of obesity at 5.5 years; the multivariable ORs (95 %CI) were 1.05 (0.81-1.35), 1.23 (0.93-1.62) and 1.54 (1.04-2.31) for sleep duration 10, 9 and ≤ 8 h/d, respectively; p-trend = 0.03. The observed association differed according to the children (child's sex, napping habits, and children frequently play at park), and family characteristics (mother's age at delivery and mother's level of education). CONCLUSION: Short night sleep duration among girls aged 2.5 years was associated with risk of obesity at age 5.5 years, suggesting the importance of sufficient sleep duration at night for the prevention of obesity.

Association of job category and occupational activity with breast cancer incidence in Japanese female workers: the JACC study.

BACKGROUND: Breast cancer represented the leading cause of cancer deaths among women in Japan. Although physical activity has been reported protective against breast cancer, scientific evidence is limited on the risk of breast cancer according to job category or occupational activity in Japanese. Our objective was to examine the association of job category and occupational activity with breast cancer incidence in Japanese female workers using the data from the Japan Collaborative Cohort (JACC) Study. METHODS: A prospective cohort study involving 19,041 women aged 40-79 years who have reported their occupational data and followed-up from 1988 to 2009. All variables were assessed by a self-administered questionnaire. Cancer incidence data were obtained from 24 areas of the JACC study through cancer population data registration, or review of hospital records. The Cox proportional hazard models were operated to calculate the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs). RESULTS: There were 138 incident cases of breast cancer during 13.3 years median follow-up period. Office workers compared with manual workers were at a higher risk of breast cancer after adjusting for reproductive health factors and physical activity indicators; the multivariable HR (95% CI) was 1.65 (1.07-2.55). Also, women who had mainly a sitting position during work compared with those moving during work had the higher risk: the multivariable HR (95%CI) of 1.45 (1.01-2.12). The excess risk of breast cancer was observed for office workers when time spent in walking was < 30 min/ day; HR (95% CI) was 1.11 (1.01-1.23), and for women mainly at a sitting position during work when time spent in walking was 30-59 min or < 30 min/day; HRs (95% CIs) were 1.87 (1.07-3.27) and 1.74 (1.07-2.83), respectively. CONCLUSION: The job category and occupational activity were associated with risk of breast cancer incidence. A high risk was observed in office workers and in women with a sitting position during work. These observed increased risks were evident in women with less daily walking activity.