# Association of Nighttime Sleep Duration at 1.5 Years With Height at 3 Years: The Japan Environment and Children's Study

## TL;DR

A study of over 50,000 children found that longer nighttime sleep at age 1.5 is linked to greater height at age 3.

## Contribution

Shows nighttime sleep duration at 1.5 years predicts height at 3 years after adjusting for multiple factors.

## Key findings

- Children sleeping ≥11.5 hours at night at 1.5 years had 25% higher odds of being tall at 3 years.
- Total sleep duration was not associated with increased height.
- The association remained significant after adjusting for socioeconomic and environmental factors.

## Abstract

Adequate nighttime sleep duration has been considered beneficial for linear growth in children; however, there is limited and conflicting evidence regarding the association between sleep duration and subsequent linear growth.

To investigate the association between sleep duration at 1.5 years and height at 3 years of age.

The Japan Environment and Children's Study is a nationwide prospective birth cohort study. Data from 52 140 term singleton births born at an appropriate-for-gestational age without background disorders that could potentially affect linear growth in the analyses were included. Nighttime and total sleep durations were calculated based on a self-administered questionnaire completed by caregivers. Tall stature was defined as height at or above the 75th percentile among participants.

After adjustment for height at 1.5 years, sex, monthly age, mother's height, presence of siblings at 1.5 years, environmental tobacco smoke at 1.5 years, daily TV/DVD screen time at 2 years, attendance at nursery at 2 years, household annual income at birth, and parents’ educational status, multivariate odds ratio (95% CI) for tall stature at 3 years were 1.09 (1.01-1.17), 1.09 (1.01-1.17), and 1.25 (1.14-1.37) for 9.5 or 10, 10.5 or 11, and ≥ 11.5 hours of nighttime sleep duration at 1.5 years, respectively, compared with those with ≤ 9 hours sleep (P for trend <.0001). Total sleep duration was not associated with tall stature.

This study underscores the importance of nighttime sleep duration, not total sleep duration, in the linear growth of very young children.