Irregular Bedtimes Impair Children's Cognitive Development

Caroline Cassels

July 08, 2013

Irregular bedtimes throughout early childhood may impair children's cognitive development and have deleterious long-term knock-on health effects throughout life, new research shows.

A large longitudinal study conducted by investigators at University College London in the United Kingdom showed that irregular bedtimes in toddlers were associated with lower cognitive test scores at age 7 years, with girls particularly affected.

"Our findings suggest that inconsistent bedtimes, especially at very young ages and/or throughout early childhood, are linked to children's cognitive development," the investigators, led by Yvonne Kelly, PhD, write.

"Relations between inconsistent bedtimes and aspects of early child development may have knock on effects for health and broader social outcomes throughout the lifecourse," they add.

The study was published online July 8 in the Journal of Epidemiology and Community Health.

Cumulative Effect

Although it is known that sleep plays a key role in maintaining healthy function, most of this evidence is based on studies in adults and adolescents, with little known about its impact in young children and their cognitive development.

The researchers note that previous small-scale studies examining its impact in a young pediatric population yielded mixed results. For the current study, the investigators aimed to examine the link between the time young children go to bed and their cognitive development in 11,178 7-year-olds who are participants in the Millennium Cohort Study (MCS).

The MCS is a nationally representative longitudinal study of infants born in the UK. The sample for the current study was drawn from births in the UK between September 2000 and January 2002.

The researchers sought to determine whether the time a child went to bed and the consistency of bedtimes had an impact on intellectual performance. They also wanted to determine whether any potential negative effects were cumulative and/or whether any particular periods during early childhood were more critical than others.

For the study, the researchers analyzed data on bedtimes from age 9 months and ages 3, 5, and 7 years. During structured interviews at home visits, questions were asked about socioeconomic circumstances, demographic characteristics, family routines, including bedtimes, and psychosocial environment.

At age 7, cognitive assessments that measured reading, mathematics, and spatial abilities were carried out by trained interviewers.

The investigators found that irregular bedtimes were most common at age 3, when about 1 in 5 children went to bed at varying times. By age 7, more than half of the children went to bed between 7:30 and 8:30 pm.

The investigators found that irregular bedtimes at age 3 were independently associated in girls and boys with lower reading (β: -0.10, -0.20), mathematics (β: -0.16, -0.11), and spatial (β: -0.13, -0.16) scores.

Further, they found that at age 7, not having a regular bedtime was related to low cognitive test scores in girls — reading, β: -0.22; mathematics, β: -0.26; and spatial, β: -0.15 — but not for boys.

The researchers also found that there was a cumulative effect, such that girls who had never had regular bedtimes at ages 3, 5, and 7 had significantly lower reading (β: -0.36), mathematics (β: -0.51) and spatial (β: -0.40) scores.

For boys, having irregular bedtimes at any 2 ages was linked to lower reading (β: -0.28), mathematics (β: -0.22), and spatial (β: -0.26) scores.

Key Health Determinant

The finding that irregular bedtimes at age 3 were linked to lower scores on all 3 study outcomes in boys and girls suggests that age 3 may be a particularly sensitive period for cognitive development, the researchers note.

As for potential mechanisms, the investigators suggest that inconsistent bedtimes could affect cognition in at least 2 ways: first, by disrupting circadian rhythms, and/or second, through sleep deprivation and its subsequent effects on brain plasticity, "including processes to do with embedding new knowledge, memory and skill into developing neural assemblies."

"Sleep is the price we pay for plasticity on the prior day and the investment needed to allow learning fresh the next day.... Early child development has profound influences on health and well-being across the life course. Therefore, reduced or disrupted sleep, especially if it occurs at key times in development could have important impacts on health throughout life," the authors conclude.

The authors report no relevant financial relationships.

J Epidemiol Community Health. Published online July 8, 2013. Abstract


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