Enlighten the night shifts of policemen in Drenthe

In the Netherlands approximately 16% of the working force is involved in night
shift work (CBS 2001). Working at night is not optimal. The processes in the
human body have evolved to be best adapted for diurnal activity and nocturnal
sleep. Unfortunately it is not always possible to work only during daytime.
People working in the health and security sector work night shifts for 24-h
availability in case of emergencies, and a lot of companies work through the
night of economical reasons. The biological clock indicates that the preferable
time to sleep is at night. In combination with long hours of wakefulness before
the night shift starts, this results in people feeling sleepy and do not
function properly at night. Shift work is also related to health problems in
general, such as sleep disturbances, heart- and coronal diseases,
gastro-intestestinal problems and metabolic syndrome. These health problems
related to shift work are categorized under circadian rhythm sleep disorders.
Vigilance and safety are focus points in police-work. During nights shifts both
these facts are at stake. In addition the working force of the police
departments suffers from an aging problem. It is well known that health
problems related to shift work become more prominent with aging. Purpose of the
present study is to counteract the negative effects of night shift work on
vigilance and safety and to improve health and general well being in general in
policemen.

Objective of the study is to test the effects of two different interventions
during the nightshift on alertness and performance and on sleep quality and
health complaints in general. The interventions are short exposure to light or
taking a powernap at prescribed times during the nightshift.

Cross-over (within subject) comparison with 2 experimental and 1 control
condition.

The 3 conditions each last 4 weeks. During the control condition subjects work
in their regular way, there is no intervention. During the light conditions
participants expose themselves during each night shift to 1 light pulse of 5000
lux during 20 minutes in the time frame between 4 and 6 a.m. In the "powernap"
condition subjects are asked to take a powernap of maximally 20 min during each
night shift somewhere between 2 and 4 a.m.

The burden for the subjects consists of filling out a questionnaire on sleep,
mood and health complaints after each condition (3 times 20 min). In addition
the participants will wear an activity meter during the whole study of 12
weeks, 24 hours per day. This activity meter is able to measure rest-activity
cycles and sleep parameters such as sleep efficiency, sleep onset etc. During
each night shift subject fill out some questions on sleepiness (1 min) and
perform some tests on reaction time and fine motoric skills (9 min) on a PDA 5
times per night (10 min each).
The study is not expected to bring any risks. It usually happens that people
suffer from sleep inertia after taking a nap. By reducing the duration of the
nap to max 20 min and by planning it in the beginning of the night, the risk of
sleep inertia is kept low. Nevertheless subjects will be advised not to sit
behind the wheel during the first 30 min after waking up if possible. By taking
these precautions the risks for sleep inertia are estimated to be not higher
then the normal risks of sleepiness during the night shift without an
intervention. In the literature there is discussion about the possible role of
light at night in increasing the risk for developing breast cancer in women
working in night shifts. Epidemiological studies do show an increased risk
after working in night shifts if women work for more then 20 years in regular
night shifts. The underlying cause is not known, but melatonin suppression by
light has been proposed as one of the possibilities. We chose a high intensity
light pulse to reduce sleepiness. This will shortly suppress melatonin, but
because of proper timing and the short duration, melatonin will only
temporarily be suppressed and will come back after turning off the light.
Therefor melatonin suppression calculated over the whole night will be minimal
keeping possible risks also very minimal.