SLEEPNormally, adults sleep between 7 and 8 hours per night. However, some may sleep less or more, creating large individual differences that may be related to age and health, stress and working hours, or social activities and drug or alcohol use.

The 7–8 hours per night sleep is regulated by the two daily cycles the human organism experiences.

These are 1. “the ready to perform cycle” (ergotropic phase) during the daylight or daytime.

2. The “relaxed phase for recovery and replenishment of energy” (trophotropic phase) during the night.

Given these two phases, working at night carries with it physiological and medical problems, not to mention family and social issues, since the person is trying to perform during the relaxed phase.

Therefore, work schedules and shift work should be designed to produce the fewest negative effects on the health, family, and social life of the individual.

The human body experiences a biological rhythm, identified by a periodic change in body physical measurements, such as body temperature, heart rate, blood pressure, and chemical response (like the production of catecholamines such as epinephrine, norepinephrine, and dopamine, and adrenalin that function as hormones, neurotransmitters, or both).

The biological rhythm fluctuates in a 24-hour cycle, known as circadian rhythm. Circadian is from the Latin word of circa (“about”) and dies (“day”). This can be referred to as endogenous (internal clock) circadian rhythm and operates on a cycle of between 22 and 25 hours and varies among individuals.

The age of the worker plays a role in sleeping patterns and disorders.As people get older, they have less sound sleep and are easier to arouse than younger people. This is experienced as more and longer nighttime awakenings, more shifts from one sleep stage to another, and more body movement during sleep. This fluctuation leads to a decrease in the restorative power of sleep (normal sleep) and an increase in daytime drowsiness and “sleepy” feelings.

The buildup of sleep deprivation (younger or older people) can lead to irritability, fatigue, inability to concentrate, and other psychological problems.

When people are allowed to sleep after prolonged sleep deprivation, they experience increased sleep duration as well as an increase in the percentage of recuperative (NREM, Stages 3 and 4) sleep.

Sleep disorders are divided mainly into three categories: inability to get to sleep or stay asleep, disrupted timing of sleep and waking as occurs with jet lag or shift work, and feeling too sleepy during daytime.

Shift work can aggravate sleep disorders by leading to a difficulty in initiating and maintaining sleep (insomnia), cessation of breathing during sleep (sleep apnea syndrome), irresistible sleepiness occurring unpredictably throughout the day (narcolepsy), and gastrointestinal reflux issues.

In addition, the consumption of caffeine and alcohol can generally lead to a decrease in length and quality of sleep, where sleep becomes lighter and more fragmented.

Ideally all jobs should be done in daytime. When working at night is unavoidable, proper importance should be given to minimize the ill-effects of lost sleep on the workers.