Environmental factors play greater role than genetic factors in sleep length

A newly published study on the effects of genetic and environmental factors on the sleep length of the working aged suggests that genetic factors do not dictate sleep length, and that it is thus possible to influence individual sleep time. According to the results of the study, environmental factors have twice the effect of genetic factors on sleep length. Medically this means that treatment may help lengthen sleep among, for example, those suffering from insomnia, who form a large group of short sleepers.

”As far as we know, this is the first longitudinal study to produce data on the effects of heredity on sleep length over a long time span. We used wide-ranging twin data and three measurement points (1975, 1981 and 1990),” says Christer Hublin, Assistant Chief Medical Officer at the Finnish Institute of Occupational Health (FIOH). “Earlier, the effect of heredity on sleep length has been studied through a questionnaire survey on sleep length at one time point and among a certain age-group; a longitudinal study of this kind increases the reliability of the results.”

”The role of genetic factors in the variance of sleep length remained almost the same at the different measurement points of the study period (30%), and the genetic factors were very stable,” Hublin explains. “Although the effect of non-genetic factors was great (70%), they varied to quite an extent between the different measurement points.”

Short sleepers double in number

Sleep length changed clearly over the 15 years of the study: the amount of short sleepers (those sleeping less than seven hours) more than doubled, whereas the proportion of long sleepers (those sleeping over eight hours) did not change greatly. The change can be largely explained by ageing, as average sleep length shortens with age.

The effect of sleep length on health has been published in many studies. According to these results, those who sleep about seven to eight hours are at the smallest health risk. Sleep length nevertheless varies according to the individual, even in the short term. The study’s researchers believe it would be interesting to examine whether variations in sleep length affect health risks.

The research data used was that of the Finnish Twin Cohort. A questionnaire survey was carried out in 1975 (11041 twin pairs aged 18 years or over), 1981 (9323 twin pairs aged 24 or over) and 1990 (4507 twin pairs aged 33–60). Sleep length was classed as short (under seven hours), average (seven to eight hours), and long (over eight hours). The study examined the results of both identical and non-identical twins according to age group and gender.

Further information:

Christer Hublin, Assistant Chief Medical Officer, FIOH, tel. +358 30 474 2120, christer.hublin[at]ttl.fi

Article: Genetic factors in evolution of sleep length – a longitudinal twin study in Finnish adults. Hublin C, Partinen M, Koskenvuo M, Kaprio J. Journal of Sleep Research, DOI: 10.1111/jsr.12051 (Article first published online: 20 Mar 2013) (http://onlinelibrary.wiley.com/doi/10.1111/jsr.12051/pdf)

The Finnish Institute of Occupational Health researches, develops and specializes in well-being at work. It promotes occupational health and safety and the well-being of workers. It is an independent institution under public law, working under the administrative sector of the Ministry of Social Affairs and Health. It has six regional offices, and its headquarters are in Helsinki. It employs just under 800 people.