All animals need it, we go crazy without it, yet, we don’t understand it well – no, I am not talking about love here, but a much less considered, although just as profound, need: The need for sleep.
Sleep is currently a ‘hot topic’ in science, because it appears that it is vital for all other major systems in our brains and bodies to function well – from how we feel , how well our muscles function, how well we concentrate, to the food choices we make. Moreover, there is growing evidence that shorter sleep is linked with a large number of diseases, such as obesity, heart disease, cancer, lowered function of the immune system and mental health problems.
Although, as a nation overall, we sleep less than ever before, individuals vary substantially in the need for sleep –your partner may be chirpy after 7 hours, whereas you may need more to feel human. Interestingly, variation occurs even in the same families and among siblings; this raises the question of whether genes play a role in determining how much sleep a person needs, because families usually share a very similar environment. However, very few large studies have looked at what influences sleep early in life, when sleep is assumed to be mainly governed by the infant’s ‘body clock’. Twins are especially useful to tease the question of ‘nature’ and ‘nurture’ apart, because twins are either 100% genetically identical; or they share half of their genes, just as ‘normal’ siblings. Both, however, usually share the same environment, because they are born at the same time. Our researchers used data from the GEMINI birth cohort, which includes twins from about 2000 families, to take a closer look at the genetic and environmental influences of sleep in young children.
Perhaps surprisingly, the results showed that sleep duration and daytime nap duration were mainly influenced by the environment. Likewise, sleep disturbance was due to environmental influences, although the genetic effect was slightly bigger than for sleep duration. This was true for both girls and boys. Although it could be argued that the carer’s schedule determines infants’ sleeping time, it would be expected that they would adjust bed-and nap times according to the infants’ needs. Unfortunately there was no data available on when the infants actually went to sleep once they were put to bed, so we cannot say for sure how long they actually slept.
This study shows that, as so often, nature and nurture both act together to influence how we behave; in this instance, how much and how well we sleep. Nonetheless, the study is important, because it shows that being a ‘morning vs. evening’ type person is indeed influenced to an extent by genes and this is apparent already very early in life. However, what is more important, the study clearly shows that the home environment is a crucial factor for providing children with a good night’s sleep. So, it might be wise to practice good ‘sleep hygiene’ (and that is not only true for kids): Remove the TV from the bedroom, have a consistent bedtime routine, put your kids to bed before 9pm if they are under 10 years old, let them fall asleep without anyone present, and limit (soft) drinks containing caffeine. That will, hopefully, help your kids, and ultimately you, too, to get the well-deserved snooze.