A dose-response relationship between short sleeping hours and childhood obesity: results of the Toyama Birth Cohort Study.

BACKGROUND: Short sleeping hours could cause obesity through increased sympathetic activity, elevated cortisol secretion and decreased glucose tolerance. The aim of this study was to clarify parental and lifestyle factors, particularly sleeping habits, associated with obesity in Japanese children. METHODS: Between June and July 1996, 8274 children (4194 males and 4080 females) aged 6-7 years living in Toyama prefecture, Japan, were investigated by questionnaire survey and the collection of anthropometric data. Subjects with a body mass index (BMI; weight in kg divided by square of height in m) greater than the age- and sex-specific cut-off points linked to adulthood overweight (BMI of 25 kg/m2 or more) were defined as obese subjects. Parental obesity was defined as a BMI of 25 kg/m2 or more. Logistic regression analysis was performed to evaluate the strength of the relationships between parental obesity or lifestyle factors and childhood obesity, adjusted for possible confounding factors. RESULTS: Parental obesity, long hours of TV watching and physical inactivity were significantly associated with childhood obesity. Although wake-up time was not related to obesity, there was a significant dose-response relationship between late bedtime or short sleeping hours and childhood obesity. Compared with children with 10 or more hours of sleep, the adjusted odds ratio was 1.49 (95% confidence interval 1.08-2.14) for those with 9-10 h sleep, 1.89 (1.34-2.73) for those with 8-9 h sleep and 2.87 (1.61-5.05) for those with <8 h sleep, after adjustment for age, sex, parental obesity and other lifestyle factors. CONCLUSION: A strong inverse association was observed in the relationship between sleeping hours and childhood obesity. Longitudinal research will be required to confirm this causality.

Parental obesity, lifestyle factors and obesity in preschool children: results of the Toyama Birth Cohort study.

The aim of this study was to clarify the impact of parental obesity and lifestyle factors on obesity in preschool children. The subjects consisted of 8941 children aged 3 years, born in 1989. Anthropometric measurements and questionnaire surveys were conducted between 1992 and 1994. Subjects of body mass index (BMI; (weight (kg))/(height (m))2) more than the age- and sex-specific centiles linked to adult overweight were defined as obese subjects. Parental obesity was defined as BMI of 25 kg/m2 or more. Logistic regression analysis was performed to clarify the strengths of parental and lifestyle factors on childhood obesity, adjusted for possible confounding factors. Odds ratios (ORs) of paternal and maternal obesity for childhood obesity were 1.70(1.43-2.02) and 2.56(2.07-3.17), respectively. There was a dose-response relationship between short sleeping hours and obesity. Compared to subjects taking 11 hours sleep or more, the adjusted OR was 1.20(0.97-1.49) for those taking 10 to 11 hours sleep, 1.34(1.05-1.72) for those taking 9 to 10 hours sleep, and 1.57(0.90-2.75) for those taking less than 9 hours sleep. Eating and exercising habits were not significantly associated with obesity. These results indicate that parental obesity and short sleeping hours are possible risk factors for obesity in preschool children.