Genetic factors in evolution of sleep length – a longitudinal twin study in Finnish adults Interview with: Christer Hublin

Apulaisylilääkäri, neurologian dosentti (Helsingin yliopisto) – Assistant Chief Medical Officer, Docent (Adjunct Professor) in Neurology (Helsinki University)
Unilääketieteen erityispätevyys (Suomen lääkäriliitto)
Sleep medicine specialist (NOSMAC/ESRS)
Työterveyslaitos – Finnish Institute of Occupational Health
FIN-00250 Helsinki Finland What are the main findings of the study?

Answer: We found in an adult twin cohort (the Finnish Twin Cohort) that the proportion of variance in sleep length accounted for by genetic effects was relatively low (about one third) but stable (correlation 0.76 over a period of 15 years.). In contrast, the proportion of variance accounted for by environmental effects was high (about 0.7) and these effects were less stable (correlation over the time period 0.18). The proportion of short sleepers was more than doubled in both genders, whereas in the proportion of long sleepers no major change was seen during the follow-up. To our knowledge, this is the first longitudinal study providing data on the contribution of genetic factors to stability and change of sleep length over time. Were any of the findings unexpected?

Answer: There was considerable change in sleep length over the 15 year period as indicated by the relatively low correlation of sleep length (0.34) between 1975 and 1990. During the last decades, many studies have been published showing a significant (in many cases U-shaped) association between sleep length and several health outcomes, usually with the smallest risk in those sleeping around 7 hours. It is interesting to speculate what other possible factors are reflected in the association between sleep length and the health outcomes, as the stability of sleep length seems to be quite low. What should clinicians and patients take away from your report?

Answer: Environmental factors have relative high effects with low stability over time, which would suggest that there are major external effects on sleep length. In clinical a context this would indicate that there are good possibilities for effective treatments for those suffering from short sleep, for example insomnia – one major subgroup among short sleepers. What recommendations do you have for future research as a result of this study?

Answer: Multiple measures are a more robust basis for genetic analyses than a single cross-sectional measure when studying the evolution of sleep length. It would be of interest to investigate whether stable or variable sleep length is important in predicting different health outcomes given that genetic factors underlie much of the stability. It is possible that the genetic factor underlying sleep length stability may also be of importance in the outcomes of interest.


Genetic factors in evolution of sleep length – a longitudinal twin study in Finnish adults.

Hublin C, Partinen M, Koskenvuo M, Kaprio J.
Finnish Institute of Occupational Health, Helsinki, Finland; Department of Public Health, University of Helsinki, Helsinki, Finland.
J Sleep Res. 2013 Mar 20. doi: 10.1111/jsr.12051. [Epub ahead of print]