Discussion
The present study shows for the first time that chronic alterations of
circadian rhythm related to stress in policemen impairs not only the
perceived stress levels and sleepiness, but also the lung function and
the pulmonary and the systemic immune response.
The association between chronic shiftwork with impaired perceived levels
of stress is clearly stablished14, while the impact of
such association in different organs and systems are less understood.
Therefore, the present study shows for the first time that policemen
working in a shiftwork scale for at least 5 years, present increased
levels of perceived stress, followed by impaired lung function and
impaired systemic and pulmonary immune response.
Significant positive associations have been observed between stress
indices and increased incidence of chronic diseases, such as
cardiovascular and metabolic diseases7,15, as well as
systemic immune dysregulation5. Herein, the present
study shows for the first time that compared with civil men working in a
continuous 8 hours/day diurnal scale, without increased levels of
perceived stress and sleepiness disturbance, policemen presented
increased levels of serum IL-2. Increased levels of IL-2 play a major
role in the growth and proliferation of many immune cells such NK and T
cells and is known as a pro-inflammatory cytokine. The activation of T
lymphocytes via interleukin IL-2 and IL-2 receptor plays an important
role in pulmonary diseases such as asthma16,17, in
which airway obstruction is present at different levels. Furthermore,
asthmatic patients have higher pulmonary levels of IL-2 compared to
healthy subjects18. In addition, several studies have
reported inverse association of pulmonary levels of IL-2 with the FEV1
in asthmatic individuals17,18. Our findings show that
police officers have higher levels of lung IL-2 compared to civilians,
which were followed by impaired lung function, an event never
demonstrated before. Of note, we reinforce that the present study
demonstrates that chronic shiftwork
scale leads to increased levels of perceived stress and impaired
sleepiness, which can be related to increased levels of pulmonary IL-2
associated with reduced lung function.
Interestingly, higher levels of pulmonary IL-2 in asthmatic individuals
present inverse association with FEV117,18. In this
way, the present study shows that non-asthmatic police officers, beyond
increased pulmonary IL-2 levels and reduced FEV1, also presented
increased levels of exhaled nitric oxide, a molecule involved with
airway inflammation and obstruction (reduced FEV1)19.
In fact, the present study showed that police officers presented
increased levels of exhaled nitric oxide, slightly above 25 parts per
billion (ppb), which significate airway
inflammation20. In addition, other sources of airway
inflammation beyond allergen-induced asthma, such as nitrogen dioxide (a
major traffic-related air pollutant)21,
lipopolysaccharide9,22,23, and
smoking24 also can increase the levels of nitric
oxide. Therefore, the present study showed that policemen working in a
shiftwork scale clearly present airway inflammation, characterized by
increased levels of exhaled nitric oxide, although the source of such
airway inflammation could not be confirmed in this study.
On the other side, increased levels of blood IL-10, an immunomodulatory
and anti-inflammatory cytokine has been associated increased and better
FEV1/FVC values, which is also an important marker of airway
obstruction25. In the present study, it was found
similar response, since policemen working in a shiftwork scale presented
reduced levels of IL-10 and reduced FEV1. These findings reinforce the
findings of previous studies performed in
asthmatics25, demonstrating a possible association
between lower levels of IL-10 with airway inflammation and airway
obstruction. In fact, this concept that low levels of IL-10 can be
associated with airway obstruction is strengthened by the present study,
since that such phenomena were also found in non-asthmatic patients. In
addition, reduced levels of IL-10 has been associated also with
increased pulmonary inflammation induced by Mycoplasma
pneumoniae 26, obstructive sleep
apnea27, and poor progression of COPD
patients28, demonstrating that perhaps, police
officers could be more susceptible to develop pneumonias, obstructive
sleep apnea and even COPD. However, the present study has not evaluated
such hypothesis and cannot confirm that policemen could be more
susceptible to develop pneumonias, obstructive sleep apnea and COPD.