Night Shifts, Circadian Rhythm And Our Health

Everyone is well aware that a fine night of sleep is essential for the maintenance of a good state of health. It does not come as a surprise, then, that disrupting the regular sleep pattern, due to night shift work in particular, can increase an individual’s risks of suffering from a myriad of medical conditions.

Each and every person possesses what is known as a circadian clock.

This sophisticated mechanism synchronizes endogenous systems with the 24-hour day, adjusting their functioning to the various parts of the day and thus establishing the circadian rhythms. Circadian rhythms control not only the sleep/wake cycles, but also more specific biological processes, such as intestinal function, body temperature and hormone secretion.  Circadian rhythms are even found at the cellular level, where transcriptional activators and repressors stimulate and repress gene expression, respectively, in a cyclic process that extends throughout approximately 24 hours.

Disruption of normal sleep pattern is seriously damaging for health

Elements of modern-day society, such as work schedules that include long-term night shifts and shift work, disrupt normal circadian rhythms. The subsequent misalignment between the original 24-hour body rhythms and the individual’s actual behavioral activities is extremely damaging. This is because not only does the sleep-wake cycles become disrupted, but also time-inappropriate cues such as nighttime light exposure and food ingestion are conflicting to the central nervous system and to the cellular mechanisms behind circadian rhythms. The consequences of such disruptions on the body are multiple and serious.

The circadian clock genes are a group of genes related to cell proliferation and apoptosis at multiple sites by a variety of mechanisms. Predictably, the misalignment of this machinery, including the kind of disruptions induced by shift work, can lead to serious conditions like cancer.

One possible mechanism of this disruption is related to the production of the hormone melatonin. Melatonin is produced by the pineal gland in the brain and plays a crucial role in regulating the sleep-wake cycle. It is released in response to darkness and helps to promote sleep by making us feel drowsy. In addition, melatonin has been found to have antioxidant properties, which may help protect against certain types of cancer

One important Norwegian investigation confirmed the increased risk of breast cancer among nurses who worked for at least 5 years with six or more consecutive night shifts. Reports pertaining to other malignancies, such as non-Hodgkin’s lymphoma, prostate, colorectal and endometrial cancers, are also known, but they require further confirmation.

Night shift workers are more likely to suffer from diabetes and obesity problems

There is a considerable body of evidence to suggest a significant relationship between abnormal circadian rhythms and metabolic changes related to obesity and diabetes in humans. The mechanism largely involves the disbalance of appetite-controlling substances.

Circadian rhythm disruptions lead to the decreased plasma concentration of the appetite-restraining adipokine leptin (produced by adipose tissue) and increased plasma concentration of the appetite-stimulating peptide ghrelin (produced mainly in the stomach). This results in greater hunger and appetite, often with an elevated preference for sweets and starchy carbohydrate-rich foods, thus contributing to a disturbed lipid and, especially, triglyceride metabolism. 

See Also: 10 Reasons You Should Go To Bed Before Midnight

A study conducted in South Korea looked at the association between shift work and the metabolic syndrome by comparing the prevalence rates of the metabolic syndrome in shift work groups and daytime work groups for female workers. The difference they found is astounding. Daytime workers had a prevalence rate of metabolic syndrome of 2.8%, while shift workers had a rate of 15.3%.

Night Shift Work Affects Cardiovascular Health And Brain Functions

Similarly to other bodily functions, cardiovascular function exhibits circadian oscillation. The severity and incidence of cardiovascular infarcts vary across time of day. The relationship between circadian disruption and increased incidence of cardiovascular events has also been reported.

These effects do not appear to be mediated by circadian deregulation alone, but rather are the product of a lack of coherence between the individual’s innate circadian timing system and the world around them.

As one would have thought, shift work has a significant negative impact on the functions of our brain, and particularly on the working memory. An investigation conducted in 90 healthcare workers, of whom 45 were night shift workers, showed that shift workers achieved significantly lower scores on verbal memory, attention–concentration, and the digit span forward sub-scales of the Wechsler Memory Scale-Revised (WMS-R), as well as on the immediate memory and total learning sub-scales of the Auditory Verbal Learning Test (AVLT). 

Diverse range of health problems is associated with night shift work

Circadian rhythm disruption also negatively impacts reproduction by altering our hormone profiles, reproductive timing, and fertility. Research is beginning to show the deleterious effects of circadian disruption during pregnancy on the offspring. Several studies have reported increased rates of preterm births and lower birth weights among women employed on shift work schedules; though there is still some debate regarding whether circadian disruption is the actual mediating factor.

Deregulation of clock gene expression has truly diverse consequences.

See Also: Prolonged Nighttime Driving Can Be Just As Hazardous As Driving Drunk

What is behind the night shift effects?

A study conducted by researchers from the University of Surrey demonstrated that working night shifts completely alters the synchronized working of certain genes. About 6% of our genes are more or less active at very specific times of the day. Working through the night eliminates this time-precise genetic expression, with obvious negative side effects and health consequences.

The bundle of scientific evidence available leaves little doubt about the problematic impacts of circadian rhythm disruption in shift workers. From cancer to cardiovascular diseases, the risks exist and are well documented. It is important to bring these issues to the attention of government agencies and business owners, as well as to raise awareness among workers for the practice of health behaviors for the risk reduction of some of those conditions.

Many professionals who work nightshifts form the backbone of society — including doctors, nurses, and other medical professionals, first-responders, and police officers. They are at our service, and our world would quickly collapse without them. Let's recognize all the ways in which they sacrifice themselves for the good of society, including through the impact of shift work.