Circadian Misalignment In Night Shift Workers

In the modern world built upon shift-based work schedules, it is important to recognize

how these shifts may disrupt our natural circadian rhythms, affecting our overall health and

wellbeing. Specifically, night shift workers are forced to undergo abrupt changes in sleep timing

and light-dark exposure.

Simulated night-shift experiments and field studies indicated that the human circadian

system is very resistant to adaptation from day to night-oriented schedules. This is seen

specifically in the lack of phase shift and dampening of important hormone rhythms, such as

melatonin and cortisol. To understand how our circadian system is affected we must first

understand the molecular mechanism that makes up the circadian clock. The core lies in the

brain’s suprachiasmatic nucleus, which produces a set of autoregulated feedback loops through

clock genes that are expressed in a 24 hour cycle. From this, the body’s peripheral tissues are

able to generate self-sustained circadian rhythms, known as “peripheral clocks”. These molecular

mechanics allow for a general day-to-day flow of bodily functions and hormones to optimize

digestion and sleep patterns.

For instance, the peak of melatonin, and trough of body temperature and cortisol,

normally occur in the first, middle, and last thirds of the nocturnal sleep period. This allows for

more peaceful and deep sleep. Melatonin production is influenced by light, which is the most

important synchronizer of the central circadian clock in humans. When the SCN receives light,

melatonin hormone production decreases, while cortisol rises. In this same way, our digestive

patterns are influenced by the ebb and flow of our metabolism. The hormone Leptin reduces

appetite and signals the cessation of food intake, while the hormone Ghrelin signals for

food-seeking behaviors in the reverse pattern of Leptin. As seen in the Ayurvedic Clock, we

should eat our largest meal at noon, when our digestive fire is the highest. Our body reflects this

principle through hormones that work in harmony with our body’s metabolic processes to allow

for smooth and productive digestion during the day. In conjunction with highest metabolic rates

during light hours, Leptin and Ghrelin typically work together in a feeding/fasting cycle to

ensure food intake at the most optimal time for our body’s digestive system.

However, when an individual is working night shifts, the nocturnal sleep period is turned

into a wake period that involves the stress of work. This circadian misalignment dampens

hormone rhythms, meaning that the peaks and valleys are not as pronounced and affective. This

results in disrupted coordination of hormones that lead to a higher presence of disease and

disorder in night shift workers. For instance, laboratory circadian medicine studies demonstrate

that night shift work leads to a decrease in Leptin levels and a blunted post-mean suppression of

Ghrelin. This results in a cycle of disrupted hunger cues, high caloric intakes at odd hours,

unhealthy glucose spikes, and overall poor metabolic health. This contributes to higher rates in

diseases like Type 2 Diabetes and Metabolic Syndrome. In terms of the dampened melatonin and

cortisol patterns, we see that the quality of sleep is poor leading to high rates of insomnia and

daytime sleepiness that can persist for years in former night-shift workers. This is seen in

experimental results when comparing night and day-shift nurses. The night-shift nurses had a

scattered and dampened melatonin rhythm in comparison to the clustered and well aligned

hormone rhythms in day-shift nurses. This dip in melatonin is known to be dangerous, as this

hormone is protective against oxidative DNA damage. Therefore, when melatonin production is

suppressed, DNA damage may accumulate faster than it can be repaired, which may contribute

to an increased cancer risk observed among shift workers. 

In addition, taking melatonin or digestive supplements that initially increase the hormones 

needed to regulate biology, over time send messages to the body that suppress their 

production and in the long term, reduce the body's ability to make them, and thereby weaken

and disrupt the system further.

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8832572/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5647832/