Irregular bedtimes in young children may be associated with reduced academic performance, a UK study has shown.
Professor Yvonne Kelly, from University College London, followed the progress of over 11,000 British children born between September 2000 and January 2002. The regularity of each child's bedtime was recorded at ages 3, 5 and 7, with the exact bedtimes logged at ages 5 and 7. At age 7, each child also took reading, maths and spatial-skills tests.
Boys and girls without regular bedtimes, the team found, performed less well in academic tests than individuals who had a more regular schedule. Girls who experienced unusually late or unusually early bedtimes - after 9pm or before 7.30pm - also had reduced academic performance which was on par with children with irregular bedtimes.
The critical age for this effect appears to be three years.
Both girls and boys who lacked a regular bedtime at this age had impaired performance in cognitive tests at age 7, while children who had a regular bedtime at age 3 but an irregular bedtime at a later stage did not show a subsequent dip in academic performance at age 7
The effects of an irregular bedtime also appear to be cumulative, with girls who consistently had an irregular bedtime at ages 3, 5 and 7 performing worse academically than their peers who only experienced irregular bedtimes at two of those ages.
The reason an irregular bedtime at an early age leads to reduced academic performance in young children is not clear. Disrupted sleep may, Kelly and her colleagues speculate, result in less optimal brain development at an early age. They also suggest that children who lack sleep at an early age may have reduced acquisition of academic skills on which they can build in later years, thus leading to impaired performance.
However, there are several other factors which, the group propose, might also have an effect on the quantity and quality a child's sleep, including overcrowding, extracurricular activities or whether they had any siblings. The discipline of a regular bedtime might also reflect on the parental input to a child's upbringing.
Once the group took these factors in to account, they found that the negative impact of an irregular sleep pattern appeared to be greater in girls than in boys.