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/