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Everyone is well aware that a fine night of sleep is essential for the maintenance of a good health state. 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 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.
Circadian clock genes are related to cell proliferation and apoptosis at multiple sites by a variety of mechanisms and, predictably, the misalignment of this machinery, including the one induced by shift work, can lead to serious conditions like cancer. Other possible mechanism of disruption is related to production of hormone melatonin.
One recent 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 considerable body of evidence for a relationship between abnormal circadian rhythms and metabolic changes related to obesity and diabetes in humans. The mechanism largely involves the dis-balance 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 elevated preference for sweets and starchy carbohydrate-rich foods, thus contributing to the disturbed lipid and, especially, triglyceride metabolism.
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%.