Chronobiology meets work life

This thesis addresses two important features of circadian biology:
sleep-wake behaviour and light patterns. Napping and light
treatment are beneficial countermeasures against sleep deprivation
and circadian disruption. Both are extremely high in shift workers,
but also normal office workers suffer from a chronic sleep
curtailment and circadian misalignment, especially on workdays. In
order to provide recommendations, the first step is to analyse how
daily life behaviour is like without any intervention. Though
shift-working times are very restrictive, the impact of chronotype
on napping behaviour in everyday work was explored. For the first
time it was shown that not only sleep duration, also chronotype and
even circadian disruption influenced shift workers’ nap behaviour.
Furthermore, first hints were provided that main sleep duration
influences nap length and that nap timing affects succeeding main
sleep. In a second study, light profiles of normal office workers
were continuously measured. This study attempted to close the lack
in regard to light exposure of our everyday life. Light patterns
were analysed separately for work- and free days. Additionally,
different effects of light on the circadian system were considered,
either compressing or expanding internal period length. Study
findings can be explained with the hypothesis that clocks embedded
themselves into the 24-hour light-dark cycle that they experienced
light at the ‘right’ internal time of day, in order to entrain
accurately to the external zeitgeber.