INTRODUCTION
In 2016, around 121.5 million individuals worldwide were diagnosed with
cardiovascular diseases, which is on par with 48% of the US population.
Almost 47% of the US adult population is affected by
hypertension [1]. The cardiovascular diseases incidence constantly
progresses in men and women as their age advance. In a data retrieved in
2016, cardiovascular diseases are responsible for more than 2,303 deaths
daily, having one person died every 38 seconds [1]. The high
morbidity and mortality rates could be reduced with appropriate risk
factors regulations. Beside primary risk factors, such as hypertension,
obesity, diabetes, and metabolic syndromes, numerous other factors like
stress and sleep disorders might impose a vital function. Additionally,
circadian rhythm disruption is investigated to be a potential
contributor to cardiovascular diseases.
Like the rest of mammals, humans have an internal timekeeper who
maintains the schedule of multiple body functions. There is an interval
where said functions peaked and an interval of stagnation when the
functions are inactive. This internal timekeeper is known as the
circadian rhythm, allocating 24 hours in a day to a ‘biological daytime’
and a ‘biological night time’, without regard to the environment daytime
or night time [2]. This variance induces modifications in body heat
and temperature and circulating levels of melatonin and cortisol [3,
4]. The circadian system comprises of the circadian oscillators and
the suprachiasmatic nucleus. The suprachiasmatic nucleus is found in the
hypothalamus, functioning as the center for control of the circadian
system. However, circadian oscillators are located in multiple
peripheral organs, such as the liver, pancreas, and. This finding
emphasizes the variation and the cyclical activity of cardiovascular
performance and metabolic capacities on differing occasions. Circadian
oscillators produce their rhythm independently. Both of circadian system
organs work in sync to deliver cyclical
functions [2].
If the connection linking the peripheral and central circadian
controllers is interrupted, the synchronization process may be
compromised. Circadian rhythm is calibrated with the day timings of the
external environment. The biological daytime is adjusted with the light
time or the daytime; nevertheless, the biological night time is adjusted
with the dark or night time. This adjustment is compromised when the
internal timings work at an unmatched time to the real day time and
harmonious with each other. This condition is described as circadian
disruption. Disruption is initiated by shift work, jet lag, sleep
disorders like obstructive sleep apnea, insomnia, et cetera. Circadian
disruption induces many metabolic and cardiovascular health problems by
damaging the physiological mechanism like blood pressure, immunity,
insulin sensitivity, control of the cardiac autonomic system, and raise
the risk of particular diseases [5].
This review focuses on the major risk factors of cardiovascular diseases
and knowledge discrepancies concerning circadian disruption and sleep
disorders as major risk factors for cardiovascular diseases or metabolic
syndromes, such as diabetes, which later incite the development of
cardiac diseases. This review will evaluate the impact of factors that
provoke circadian disruption, such as sleep disorders or shift work, to
cardiac diseases. By approaching problems to benefit prevention measures
of cardiovascular diseases, improved health in those with cardiovascular
diseases is expected.
REVIEW
Methods
Online database of PubMed was systematically searched as a
means of data retrieval. Specific investigations of randomized
controlled clinical trials (RCTs) were done, especially those evaluating
the relationship of circadian disruption due to shift work or sleep
disorders with cardiovascular diseases. The keywords being used are:
circadian disruption, insomnia, shift work, cardiovascular risk, cardiac
diseases, and arrhythmias. The keywords are used in combination or alone
to examine published studies from the last five years. Fifty papers
written in English were obtained, and twenty papers were finally
selected following removals of duplicate papers and abstract reviews.
Next, the application of inclusion and exclusion criteria were
performed, which kept only 12 papers. Eight articles were concluded
following comprehensive reviews. Chosen papers were all appraised for
quality and
peer-reviewed.
Inclusion and Exclusion
Criteria
First, papers written in English from the past five years
assessing the relationship of circadian disruption and cardiovascular
diseases were included. Only papers that have been peer-reviewed were
selected. Research articles in different languages other than English,
unpublished studies, or review papers were eliminated. Papers which
evaluate the immunologic or metabolic effects of circadian disruption
were furthermore
eliminated.
Results
Of all eight clinical trials that are chosen, four of those evaluated
the role of working in a shift as the cause of circadiandisruption in cardiovascular diseases [6, 7, 8, 9]. Between
those studies, five evaluated the issues which are related to sleep,
like a lack of sleep, obstructive sleep apnea, and insomnia as the
factors contributing to cardiovascular diseases [8, 10, 11, 12, 13].
Only one of those studies evaluated all three of the mentioned factors
as a potential factor which contribute to the development of
cardiovascular diseases [7]. The chosen studies from the review are
presented in Table 1 [6-13].
Table 1. A comparison table of randomized controlled trials
included in the review