Going to bed at different times every night appears to reduce children's brainpower, a new British study suggests.
The research included 11 000 children in the United Kingdom whose family routines, including bedtimes, were recorded when they were aged 3, 5 and 7. At age 7, the children were given tests to assess their math and reading skills and spatial awareness.
Irregular bedtimes were most common at age 3, when around one in five children went to bed at varying times. By the age of 7, more than half the children went to bed regularly between 7:30 p.m. and 8:30 p.m.
At age 7, girls who had irregular bedtimes had lower scores on all three tests than girls with regular bedtimes. This was not the case among 7-year-old boys, according to the study, which was published online in the Journal of Epidemiology and Community Health.
Irregular bedtimes at age 5 were not associated with poorer brainpower in girls or boys at age 7. But irregular bedtimes at age 3 were associated with lower scores in reading, math and spatial awareness in both genders, suggesting that around the age of 3 could be a sensitive period for the development of mental skills.
The impact of irregular bedtimes seemed to be cumulative. Girls who never had regular bedtimes at ages 3, 5 and 7 had significantly lower reading, math and spatial-awareness scores than girls who had consistent bedtimes. The impact was the same in boys, but at any two of the three ages.
Irregular bedtimes could disrupt natural body rhythms and cause sleep deprivation, harming children's ability to acquire and retain information, the researchers said.
"Early child development has profound influences on health and well-being across the life course," said study author Amanda Sacker, from the department of epidemiology and public health at University College London. "Therefore, reduced or disrupted sleep – especially if it occurs at key times in development – could have important impacts on health throughout life."
While the study found an apparent connection between irregular bedtimes and reduced mental acuity, it did not prove cause-and-effect.
The Nemours Foundation offers parents a list of bedtime basics.