The influence of heredity on self-reported sleep patterns in free-living humans.

The heritability of self-reported sleep patterns was investigated with 86 identical and 78 fraternal same-sex and 51 fraternal mixed-gender adult twin pairs who were paid to maintain 7-day diaries. Linear structural modeling was applied to investigate the nature and degree of genetic and environmental influences and revealed significant genetic influences on the time that individuals went to sleep and woke up, how often the individual woke up during the night, the duration of sleep and wakefulness, and how alert the individual felt upon waking and over the day, accounting for 21% to 41% of the variance. These influences of heredity were present for sleep-wake behavior over the entire week and also when the sleep-wake pattern was analyzed separately for weekdays and weekends. Further, it was demonstrated that there were multiple independent influences of heredity on sleep-wake behavior. The results suggest that sleep-wake patterns are not learned but result in part from multiple heritable influences.