Our body’s circadian rhythm can be thought of as an internal 24-hour biological clock that regulates and synchronises our body’s physiological processes according to the natural patterns of daylight and darkness.

This internal biological clock will instruct the brain to release more melatonin – a sleep-inducing hormone – when it detects less sunlight in the external environment. This is why most people feel sleepy at night.

“Shift workers work odd hours and under artificial indoor lighting. During a night shift, the body will adapt to the changed sleep wake pattern. When this pattern of wakefulness at night is persistent over days and weeks, hormonal adjustments will occur to allow us to adapt to staying awake at night and sleeping in the day,” say​s Dr Fong Yuke Tien​, Senior Consultant and Director of Occupational Medicine, Department of Internal Medicine, Si​ngapore General Hospital (SGH), a member of the SingHealth​ group.

Shift workers who experience ​​headaches, insomnia, excessive sleepiness, and poor concentration could be suffering from shift work sleep disorder (SWSD). SWSD is caused by continuous sleep deprivation and interruption.

When work is continuous over long hours with no rest break, fatigue sets in and a sleep debt will accumulate. Such workers will be less attentive and more prone to accidents. Working with heavy machinery, fine work and work requiring high-attention span can become problematic.