Irregular bedtime may influence healthy brain development of young children, according to a study of intelligence and sleeping habits. Going to bed at a different time each night affected girls more than boys, but both got worse on mental tasks than children who had fixed bedtime, researchers found.

The effect was most striking in three-year-olds, where boys and girls scored lower on reading, maths and spatial skill tests than children of the same age who kept to a more strict schedule. Scientists said the lack of routine might weaken early development by disturbing the body clock, or through sleep deprivation (剥夺), which affects the brain’s ability to remember and learn new information.

“If a child is having irregular bedtime at a young age, they’re not synthesizing all the information around them at that age, and they will get a harder job to do when they are older”, said Amanda Sacker, one of the researchers. Irregular bedtime throughout childhood appeared to have accumulative effect, leading to greater problems later on.

Sacker and her colleagues drew on information in the UK Millennium Cohort Study (MCS), a long-term record of UK children who are now in or approaching their early teenage years. They looked at how the children’s performance were on tests at various ages, and whether bedtime had any impact. Parents who took part in the MCS were asked whether their children went to bed at a regular time on weekdays. Those who answered “always” or “usually” were put in the regular bedtime group in Sacker’s study, while those who answered “sometimes” or “never” were put in the irregular bedtime group.

Sacker suggests that irregular bedtime affects the brain’s ability to store and learn new information. Early child development has deep influences on health and wellbeing across the life course. Therefore, reduced sleep, especially if it occurs at key times in development, could have important impacts on health throughout life.