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