Decreasing social jetlag with blue-light reducing glasses in the evening compared to blue-LED-light emitting glasses in the morning

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, 75% 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 e.g. shift-work occupations. This
problem especially affects later chronotypes (people 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).
Studies of our workgroup have shown, that social jetlag is significantly
positively associated with an increased risk of smoking, obesity, and heart
rate (especially in shift-workers).
Because blue light is the main zeitgeber regulating the timing of sleep (via
synchronisation of our internal clock), 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. The published literature shows the potential of additional
morning blue light exposure from blue-light emitting devices to advance sleep
onset and also the circadian phase of melatonin significantly. In addition,
recent studies strongly suggest that it is especially blue light in the
evenings and primarily from TV*s, LED*s and computer/tablet screens that delay
sleep timing, hence resulting in higher social jetlag. Two recent studies
tested blue wavelength light blocking (reducing) glasses (worn from 3 hours
before bedtime) and showed significant improvements in subjective sleep
quality. These studies only tested small numbers of participants and only
assessed subjective parameters, and argued in favour of future studies with
larger sample sizes and objective parameters. However, no study compared the
effect of (i) blue light reduction in the evenings compared to (ii) increased
blue light exposure in the mornings in the same participants to decrease social
jetlag. In the current study we, therefore, combine in a cross-over
within-subject study the effect of controlled morning light exposure and
controlled shielding from evening light tested in separate weeks on sleep
timing, social jetlag and circadian phase of melatonin from saliva samples.

To elucidate in the same participants (late chronotypes with at least two hours
of social jetlag) the changes in sleep timing, social jetlag and endogenous
circadian phase of melatonin with more than two hours of social jetlag shielded
from blue light in the evenings compared with increased blue light exposure in
the mornings.

Interventional field study; Applying a cross-over study design we will equip
participants with short wavelength (blue) light reducing orange glasses
(experimental condition 1) to be worn for at least three hours before sleep
onset for seven days. The same participants will be equipped with
blue-LED-light emitting glasses to be worn for two hours after wake up
(experimental condition 2) for seven days. Effects will be measured by
comparing each intervention period with a seven days baseline period.

Short wavelength (blue) light reducing orange glasses (blue light absorption
>93%; appendix D1b; experimental condition 1) for seven days for at least three
hours before sleep time (lights out; when waking up during the night, e.g. to
use the toilet, participants will be asked to put on the glasses before
switching on the room lights), and blue-LED-light emitting glasses
(www.enwake.me; comparable to the Philips goLITEblu devices; appendix D1c;
experimental condition 2) for two hours after wake up. The order of
experimental glasses 1 and 2 will be randomized.

There are no known or expected adverse events from participating in our study.
The only intervention is to wear orange/amber glasses in the evening and to
complete questionnaires. We do not apply any severe or acute sleep deprivation
protocol. All participants will have at all days the possibility to sleep at
home without interfering with their normal daily routines.