Hormonal Changes In Satisfied And Dissatisfied Shift
Workers
Across A Shift Cycle
To better understand the variation
in tolerance of shift work, researchers focused on the endocrine differences
between two types of shift workers. Results show that dissatisfied shift
workers accumulated problems with sleep and fatigue across a work period
September 10, 2003 - Bethesda, MD -- There is
ample evidence that shift work, including night work, increases the risk for
developing both psychological and physiological health problems. The most
well established links exist between shift work and increased risk for
cardiovascular heart disease, gastrointestinal disorders, and clinical sleep
disorders. The risk for these problems increases with the number of years of
exposure to shift work and it is believed that the main cause of the
increased illnesses is due mainly to the disruption of sleep/wake behavior
and the resulting conflict with the circadian system. To date, there is
limited knowledge of the mechanisms behind disease susceptibility in shift
workers. A new study contributes to the growing body of knowledge.
Background
Studies have shown that sleep in shift workers is often
displaced and/or shortened, particularly in connection with morning and
night shifts. Several laboratory studies confirm that such sleep
disturbances alter the regulation of several hormones – including cortisol,
prolactin and growth hormone – in both shift/night workers as well as other
populations. Workplace studies have shown that working nights and being
on-call are not only related to increased adrenalin release, but also to
reduced levels of testosterone.
A New Study
While the main negative effects of shift work are well
documented, not all individuals are affected equally. In an attempt to
better understand the variation in tolerance of shift work, researchers have
focused on the endocrine differences between two types of shift workers,
satisfied and dissatisfied. Their results show that the dissatisfied shift
workers accumulated problems with sleep and fatigue across a work period.
The study, entitled “Hormonal Changes in Satisfied and
Dissatisfied Shift Workers Across a Shift Cycle,” was conducted by John
Axelsson, Torbjörn Åkerstedt and Göran
Kecklund, all of the National Institute for Psychosocial Factors and Health,
Stockholm, Sweden; Anne Lindqvist of the Karolinska Institutet, Stockholm,
Sweden; and Reine Attefors, of Hyltehalsan, Hyltebruk, Sweden. Their
findings appear in the online section “Articles in Press” of the Journal
of Applied Physiology. The journal is one of 14 scientific journals
published monthly by the American Physiological Society (APS) (www.the-aps.org).
Methodology
A total of 317 of 368 full time shift workers working
as control room operators, shift engineers, machinists and shift supervisors
at a paper and pulp factory in Sweden filled out a questionnaire where they
rated their “satisfaction toward their work hours” (1 = very dissatisfied, 5
= very satisfied). These ratings were used to divide the shift workers into
two groups that were either satisfied or dissatisfied with their shift
schedule. The shift system had been in use for more than 20 years.
A total of 62 male shift workers were invited to
participate in two health examinations where blood was drawn. Eventually,
the study group included 42 men, of which 22 were satisfied (mean age of 44
years) and 20 dissatisfied (mean age 41 years). Relatively few shift workers
were dissatisfied with their work hours; therefore, the resulting difference
between satisfied and dissatisfied shift workers was 5.0±0 vs. 2.4±2.
The shift cycle (comprising 35 days and 5 shift teams)
rotated rapidly and included 7 work periods (triads) and one week off. A
“work period” consisted of three shifts during four days, with 8 hours off
between the night- and afternoon-shift, and 9 hours off between the
afternoon- and morning-shift. Each shift worker was examined twice, at the
beginning of the morning shift during the first and the last of the seven
work periods.
Fasting blood samples were obtained between 0700h and
0900h on the morning-shift during the first and the last (7th)
work period and examined. The data were analyzed using repeated-measures
analysis of variance (ANOVA) with 1 between-group and 1 within-group
measurements.
Results
The investigators found that:
-
Dissatisfied shift workers had lower morning testosterone
levels than satisfied ones, but the two groups did not significantly
differ with respect to levels of cortisol or prolactin.
-
The only significant change across the shift cycle was the
lowering of morning levels of cortisol on the last morning shift in the
shift cycle.
-
In light of the testosterone results, they hypothesize that
the low levels of testosterone may be due to disturbed sleep and/or a high
sleep need, which in turn may result in more sleepiness and a greater need
for recovery after a work period, and as a consequence, dissatisfaction
with the shift schedule.
Conclusions
The results suggest that dissatisfaction with the shift
system is related to lower testosterone levels, and that the latter are
related to disturbed sleep/wakefulness and an increased need for sleep and
recovery. In addition, working an entire shift cycle was related to a
decrease of morning cortisol, which may relate to an adaptation to long-term
stress.
Low testosterone levels and disturbed sleep might be
key factors for developing shift intolerance, mainly by reducing the
capacity to recover from shift work. Studies using larger sampling
procedures are necessary to shed further light on the mechanisms involved in
intolerance to shift work.
-end-
Source: Journal of Applied Physiology
(Articles in Press)
The American Physiological Society (APS)
was founded in 1887 to foster basic and applied science, much of it relating
to human health. The Bethesda, MD-based Society has more than 10,000 members
and publishes 3,800 articles in its 14 peer-reviewed journals every year.
***
Editor’s
Note: Members of the press are invited to obtain a pdf version of the study
and to interview members of the research team. To do so, please contact
Donna Krupa at 703.527.7357 (direct dial), 703.967.2751 (cell) or djkrupa1@aol.com.
