Longitudinal changes in sleep patterns and circadian rhythm metrics in preschool-age children from Northern Mexico

Objectives: To assess changes in sleep parameters and circadian rhythm metrics measured by actigraphy in preschool-aged children. Design: Longitudinal analysis over 1 year. Participants: Ninety-four children living in Tijuana and Ensenada, Mexico. Measurements: Children wore accelerometers on the right hip for one continuous week at baseline and 1-year follow-up. Parents recorded child bedtime, waketime, and naps in sleep diaries. We used cosinor and nonparametric approaches to calculate circadian rhythm metrics. Results: At baseline, children had a mean age of 4.2 years, and 51.1% were girls. In multivariable models adjusted for age, gender, BMI category, parental education, household income and city, at follow-up children had significantly earlier waketimes (β = -7.99 minutes, p <.001) compared to baseline. Children also had lower sleep onset latency (β = -2.32 minutes, p =.057), and longer nighttime sleep (β = 9.38 minutes, p =.079), but these changes were not significant at the α < 0.05 level. We found significant increases in log relative amplitude (β = 0.017, p =.009), and decreases in log midline estimated statistic of rhythm (β = -0.084, p =.017) and log of the least active 5-hour period (β = -0.057, p =.010). When we adjusted for co-sleeping, we found significant decreases in the number of nighttime awakenings (β = -1.29, p =.011) but otherwise similar results. There were no other changes in sleep parameters or circadian rhythm metrics. Conclusions: Mean increases in nighttime sleep and earlier wake times over one year were concomitant with decreases in overall activity levels and increases in circadian rhythm robustness. Co-sleeping was a predictor of sleep disturbances. This study provides longitudinal evidence regarding changes in sleep and circadian metrics in a sample of children from an under-researched sociodemographic group during an important, early life period.