Short sleep duration in middle childhood: risk factors and consequences.

STUDY OBJECTIVES

To measure sleep duration in 7-year-old children; identify the determinants of sleep duration; and assess the association between short sleep duration and obesity, cognitive functioning, and behaviour.

DESIGN

Longitudinal study with disproportionate sampling of the participants.

SETTING

Community.

PARTICIPANTS

591 seven-year-old children, of whom 519 had complete sleep data.

INTERVENTIONS

Not applicable.

MEASUREMENTS

Sleep duration was assessed by actigraphy. Other measurements included height, weight, BMI, percentage body fat as assessed by bioimpedance assay, intelligence (WISC-III) and behaviour (Strengths & Difficulties questionnaire, parent and teachers Conners Rating Scales).

RESULTS

Mean time in bed according to parental report was 10.9 hours (SD 0.8). Mean sleep duration by actigraphy was 10.1 (SD 0.8) hours. In multivariable analysis, sleep duration was longer on weekdays vs. weekend nights (31.5 min, P = 0.002), in winter (40.5 min), autumn (31.1 min), and spring (14.8 min) compared with summer (P <0.0001), and in those with younger siblings (11.7 min, P = 0.03). Sleep duration was shorter when bedtime was after 21:00 (-41.1 min, P <0.0001). In multivariable analysis, sleep duration <9 hours was associated with being overweight/ obese (BMI: OR = 3.32; 95% CI = 1.40, 7.87) with an increase of 3.34% body fat (P = 0.03), and this was not explained by physical activity or television watching. Short sleep duration was also associated with higher emotional lability scores (Conners Rating Scale Parent Form; P = 0.03). IQ (WISC-III) and attention deficit / hyperactivity disorder scores (both parent and teachers Conners Rating Scales) did not differ with sleep duration.

CONCLUSIONS

Sleep duration in 7-year-old children varies considerably among individuals. The duration is affected by weekday, season, and having younger siblings. Importantly, short sleep duration was shown to be an independent risk factor for obesity/overweight.