Researchers from Japan's Environment and Children's Study tracked sleep patterns in nearly 50,000 toddlers at 18 months old, then measured their growth by age 3. They wanted to understand whether the timing of bedtime—not just the total amount of sleep—affected how much children grew.
The study followed toddlers' sleep habits and compared growth outcomes across different bedtime groups, looking at both when children went to sleep and how many hours they slept overall.
Children with 8pm–10pm bedtimes grew more than late sleepers
Toddlers who went to bed between 8pm and 10pm showed slightly more growth over two years than those sleeping after 10pm or 11pm. The difference was small—just a few millimetres—but it appeared consistently across the large sample. Importantly, children who slept very little overall (less than 11 hours) didn't benefit from an early bedtime, showing that both timing and total sleep duration matter for growth.
Night wakings didn't affect growth, but bedtime did
The research found that how often toddlers woke during the night made no difference to their growth. Instead, what mattered was when they fell asleep and how many total hours they slept. This distinction is useful for parents: you might worry less about occasional night wakings and focus more on establishing an earlier, consistent bedtime and ensuring adequate total sleep.
Why this timing might matter for Singapore families
Growth happens largely during deep sleep, which occurs more readily in the early night hours. An earlier bedtime helps children reach those deep sleep phases at their peak. For Singapore families balancing work schedules, tuition, and screen time, it's tempting to assume that 10 hours of sleep is the same regardless of clock time. This research suggests the 8pm–10pm window offers an advantage worth targeting.
One limitation: the study was conducted in Japan, so findings may not apply identically in Singapore's different climate, activity patterns, and family routines. The research shows association, not proof of cause-and-effect. Other factors like nutrition, genetics, or family resources could partly explain the difference.
Adjusting bedtime to support your toddler's growth
- Aim for a bedtime between 8pm–10pm, which showed the growth advantage in this study of nearly 50,000 children.
- Prioritise at least 11 hours of total sleep nightly; early bedtime alone didn't help children who slept too little overall.
- Discuss your toddler's bedtime and sleep habits at health check-ups; it's one factor you can influence directly.