Need for Sleep Is Inherited

The need for sleep is really variable from person to person. Albert Einstein needed eleven hours to rest. Napoleon, on the other hand, was allegedly satisfied with four; the same is told of the former British Prime Minister Margaret Thatcher.

The season of the year, along with age and sex, all play part in how much you need to sleep. The pattern of circadian activity – chronotype – is also important. You may be an early bird who wakes up and goes to sleep early or an “owl” who likes to stay awake late at night and sleep long in the morning.

Research with identical twins revealed that about 40 per cent of the need for sleep boils down to heredity. The role of genes is becoming ever clearer. A major international study figured out the first gene variant that is an important factor in sleep requirements.

Tartu Autumn Days 2012

Getting up early in the morning can be tough, but seemingly not for these guys – they have come out at 6.15am this Monday to get the Tartu Student Days going with the ‘wake-up call’ exercise. Photo by Erki-Heiki Meerits.

Till Roennberg from the Ludwig Maximillian University of Munich led the work group that analysed gene samples of more than four thousand persons from seven European countries. A little more than a thousand samples by donors of the Estonian Genome Project were also included.

The guinea pigs had to fill out an in-depth questionnaire where they answered questions about their usual bedtime, how long it takes them to fall asleep, usual time to wake up, if an alarm clock was necessary, etc.

“It would’ve been really nice if we’d been able to examine everybody in the sleep lab, but unfortunately it’s not possible”, explained researcher Maris Teder-Laving of the Estonian Genome Project.

The questionnaire, developed in the University of Munich, has been verified and it seems that people’s evaluations of their need for sleep are quite accurate. In this study, only the need for sleep on rest days was taken into account, because on workdays even the “owls” may not be able to escape waking up early. The scientists used the questionnaires when working with the human genome, trying to find patterns.

It turned out that individuals with a certain variant of the ABCC9 gene had less sleep on average than those with another variant. This variant added half an hour to the average need for sleep, and one European in five has this bit of DNA.

The gene encodes a protein that deals with information concerning energy levels in the cells. In the human body, ABCC9 is active in the brain, heart, muscles and pancreas.

“Sleep is regulated in a very complex way. This particular gene regulates metabolism and is important in case of diabetes and high blood pressure”, noted Teder-Laving.

Even insects have the gene. Vinegar flies, a hugely popular model organism in biology, also fall into state of rest that resembles sleep. When scientists blocked the manifestation of the gene, the insects’ night sleep decreased by three hours on the average. “Flies sleep at both daytime and night but this gene influenced only the length of the night sleep. It is a good proof that the gene variant has a very strong impact on the length of sleep”,  added Teder-Laving.

Interestingly, when verifying results of the association study that was performed on 6,000 gene donors from Estonia, it appeared that the impact of the gene variant could be easily spotted on gene donors who had their samples collected in winter, when Estonia is on standard time rather than summer time. The connection wasn’t that evident with the gene samples that had been collected in summer. “There’s an increasing amount of data showing that shifts in the time zone have a really strong influence on people”, said Teder-Laving. Allebrandt, K., Amin, N., Müller-Myhsok, B., Esko, T., Teder-Laving, M., Azevedo, R., Hayward, C., van Mill, J., Vogelzangs, N., Green, E., Melville, S., Lichtner, P., Wichmann, H., Oostra, B., Janssens, A., Campbell, H., Wilson, J., Hicks, A., Pramstaller, P., Dogas, Z., Rudan, I., Merrow, M., Penninx, B., Kyriacou, C., Metspalu, A., van Duijn, C., Meitinger, T., & Roenneberg, T. (2011). A KATP channel gene effect on sleep duration: from genome-wide association studies to function in Drosophila Molecular Psychiatry DOI: 10.1038/mp.2011.142

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