Adults shifted onto a move their body clock earlier, and whether children do the same was unclear. Children also differ in one respect that matters: their sleep habits are partly imposed. So two groups of healthy ten-year-olds spent about two weeks camping with little artificial lighting, one waking before sunrise and one waking with it, and had their melatonin timing sampled before and after.
Melatonin onset moved roughly two hours earlier. advanced by about two hours after the camping program in both groups, compared with their timing in ordinary life. The size of the shift depended on where each child started: the advance correlated strongly with their beforehand, so the children with the latest habits moved the furthest. Waking with sunrise lined melatonin up with sunset.
A natural light-dark cycle without electrical lighting advances the in adults, which has been shown more than once. Whether the same holds for children, whose sleep timing is partly set by their parents and partly by their own developing clock, was not clear.
Two camping programs ran for about two weeks each with little access to artificial lighting. Twenty-one healthy children, mean age 10.6 years, took part in a program where wake time was earlier than sunrise. Another 21 children, mean age 10.4 years, woke at a time almost matched to sunrise. Salivary dim light melatonin onset was sampled before and after.
In both conditions melatonin onset advanced by approximately two hours relative to the children’s timing in daily life. The advances also correlated strongly with each child’s mid-sleep point before the camp, in both groups. That correlation means the shift was largest for the children whose sleep habits had been latest.
The two wake times produced different endpoints. In the earlier-waking group, mean melatonin onset after the camp fell before natural sunset, and the spread between children did not narrow significantly. In the group waking with sunrise, mean onset matched natural sunset time. Note the design limits: twenty-one children per group, and no comparison group that stayed at home, so this is a before-and-after result inside a camp that changed many things together.
wat. Two weeks of camping without electric light pulled these children’s melatonin about two hours earlier, and moved the late sleepers most of all.
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It puts a number on what removing electric light does to a child, and the number is large. It also shows the effect is not uniform, since the late sleepers had the most to gain.
How do we know?
Eto and colleagues ran two camping programs with 21 healthy children each, one waking at four in the morning and one at five. Salivary dim light melatonin onset was sampled before and after about two weeks.
What is still unknown
Twenty-one children per group, with no group that stayed home for comparison, so the shift is a before-and-after measurement inside a camp that changed light, waking time and much else at once.
Learn something?
Where to next
What shape does human sleep take when the nights are long?melatonin
What is the difference between jet lag and tiredness from a long flight?body clock
What keeps time in a body that has no clock in it?melatonin