Note: RCT = randomized controlled trial; ACS = acute coronary syndrome; STEMI = ST-elevation myocardial infarction; PCI = percutaneous cardiac intervention; CBT = cognitive behavioral therapy; SS = sleep seminar; TCC = Tai Chi CHIH

As many as three clinical trials from the past five years were discovered to evaluate the impact of working in a shift on cardiovascular diseases. However, two studies did not assess the job characteristics in the shift, or the intensity and stress included that may heighten its impact on the risk of cardiovascular diseases. Consequently, the exact elevation in risk imposed in working in a shift could not be thoroughly estimated.

The internal system, or known as the circadian rhythm, is accountable for well-ordered roles of the immunological and metabolic systems. The release of cortisol is correlated with the moderation of the circadian rhythm; cortisol begins to increase several hours after sleep, peaked in early in the morning and in the hours of awakening, promoting the body to shift from biological night time to biological daytime. Any sleep disturbances influence the release of circadian; it rises in wakefulness, insomnia, or reduced sleep. Likewise, working in shift disturbs the regular pattern of release, induces lethargy, and causes the release of epinephrine and norepinephrine, sequentially affecting the variability of the heartbeat, heart rate, and blood pressure. Melatonin begins to rise after nightfall, peaked by midnight, then progressively declines in the following half. Working conditions with rotating shift provoked abnormality in melatonin concentration [14]. Melatonin concentration is related to the occurrence of cardiovascular events. It was found to be decreased in coronary artery diseases (CAD) patients. The lower the concentration of melatonin, the more the risk of cardiovascular events, such as myocardial infarction (MI). It confirms that the severity of cardiovascular diseases was inversely proportional to melatonin levels [15]. Several cardiovascular variables were modified in a diurnal pattern with the circadian pattern, involving blood pressure, heart rate, and the activity of fibrinogen [16]; and also platelet activity, endothelial function, vascular tone, and lipid metabolism [17], which partially reveals high occurrence of cardiovascular events in the morning following the circadian rhythm [17]. In 2011, Sheer at al. explained the relationship between the activity of platelets with circadian rhythm [18], which was seen to be most eminent in early daylight [19]. These variations occur by the intrinsic circadian rhythm; hence, peripheral oscillators reflect the circadian rhythm and are influenced by circadian disruption. Added factor in predicting cardiovascular diseases’ risk is the concentration of inflammatory markers, such as interleukins [20].