Decreasing social jetlag with blue light

Many physiological processes are rhythmic and differ between people, for
example our sleep-wake times or daily levels of alertness. An internal
biological clock regulates these rhythms and the daily light/dark cycle is
essential for ensuring that our body clock is synchronised to the 24-hour day.
However, 80% of the population must use an alarm clock to awaken on workdays.
By definition these people are chronically sleep deprived. From controlled
laboratory studies, there is ample evidence showing the detrimental effects of
sleep deprivation on health and performance, with consequences that would be
catastrophic in real life, especially in shift-work occupations. This problem
especially affects later chronotypes (with a later phase of entrainment), which
primarily show an increased risk of chronic sleep deprivation, a phenomenon
that has also been coined social jetlag. Chronotype (e.g. *owls* vs. *larks*)
is assessed via the Munich Chronotype Questionnaire based on calculating the
mid-point of sleep on free days (MSF) and workdays (MSW), with the MSF being
corrected for sleep deficit accumulated across the workweek (MSF sleep
corrected, MSFsc). Social jetlag is quantified as the difference between MSF
and MSW, and is a marker for chronic physiological stress resulting from a
mismatch between social and environmental/biological time. Having social
jetlag, thereby, simply infers that one lives in a given time zone but works
*in* a time zone further east (comparable to jetlag from traveling but without
the actual travelling). This major societal problem can be greatly improved
with a better understanding of the variety of responses of the human biological
clock to the timing and intensity of both light exposure and light avoidance *
especially in respect to short wavelength light which is most important to
synchronise our internal clock. Previous studies from our group (METC2010/127
and METc 2011/056) have shown the potential of controlled morning blue light
exposure to advance the circadian phase of melatonin significantly. These
studies tested small numbers of participants and argued in favor of future
studies with larger sample sizes. Therefore, we aim to study more individuals
to guarantee sufficient statistical power and additionally assess objective
sleep timing through actigraphy measures.

To elucidate the changes in the timing of sleep and waking in different
chronotypes (e.g. *owls* vs. *larks*) with at least 2 hours of social jetlag
exposed to short wavelength (blue) light in the mornings upon awakening using
Philips goLITE blu devices.

Interventional field study; We will provide 100 participants (with a social
jetlag of at least 2 hours) with Philips goLITE blu devices (as used in
METC2010/127 and METc 2011/056) for an exposure to short wavelength light of 30
minutes in the morning across 14 days. 14 days before that (Baseline) and
during the 14 days of using the goITE blu, participants will complete sleep
diaries and will wear actiwatches to assess sleep timing. In the analysis we
compare the 14 days intervention period with a 14 days baseline period.

Short wavelength light exposure via Philips* goLITE blu devices (appendix D1a
and D2b) for 30 minutes in the mornings upon awakening for 14 days (except free
days). In addition, participants will fill out a daily sleep log and wear an
actiwatch (appendix D2a). At study start, participants will complete the Munich
Chronotype Questionnaire (MCTQ).

We do not expect adverse events from participating in our study, based on our
experience with comparable protocols (METC2010/127 and METc 2011/056). The only
intervention is to sit for 15 minutes in front of a Philips goLITE blue device
at 50 cm distance in the morning only on workdays and not on free days. All
measurements will be performed at the participants* home and participants will
throughout the study follow their normal daily routines and will not be
instructed to follow pre-defined sleep times. The participants may benefit from
the treatment with improvements in sleep quality, a reduction in daytime
sleepiness and increased performance during the day. We do not expect any
negative effects on these parameters from participating in our study.