While most people sleep at night, millions of workers around the world start their work hours in night shifts, but this pattern may impose a hidden health cost on their bodies. Disruption of the circadian rhythm not only causes fatigue, but may also be linked in the long term to an increased risk of heart disease, stroke, some types of cancer, and memory disorders.

Professor Russell Foster, a sleep scientist at Oxford University who has dedicated his career to studying the biology of the brain during sleep, told the BBC: 'Sleep is a cornerstone of our health, just like diet and exercise. We must take control of it.'

He added: 'In this context, the impact of shift work becomes clear: it's not just about feeling tired, but can go as far as disrupting a system that performs more vital functions than many realize.'

Below are the hidden health costs of night work:

Effects on the brain

During sleep, our brain strengthens the day's memories, processes emotions, and solves problems it couldn't solve during waking hours.

One of the most notable discoveries in recent years is that the brain cleans itself during sleep. Deep in the gray matter, there is a system called the glymphatic system, where fluid flows through tiny channels alongside blood vessels in the brain to remove waste accumulated during waking hours.

Among the waste this system disposes of are proteins called amyloid and tau, which are the deposits that accumulate in the brains of Alzheimer's patients. A single night without sleep can significantly raise amyloid levels in the fluid surrounding the brain. If this is repeated year after year, the consequences would be worrying.

A Swedish study by researchers at the Karolinska Institute, which tracked more than 13,000 shift workers, including night shift workers, for up to 41 years, showed that midlife shift work is associated with a 36% increased risk of dementia, with the risk increasing the longer one works shifts.

Foster is careful not to overstate the link, saying, 'We cannot say that lack of sleep causes dementia, but if a person is predisposed to it, it is a potential risk factor.'

Harm to heart health

An analysis of 35 studies published last year showed that reducing sleep to about 4.5 hours for three nights or more significantly increases immune system activity. This is usually beneficial when the immune system is stimulated to fight infection, but it also causes inflammation in the body, which, if persistent, is linked to heart disease.

Increased risk of diabetes

Sleep disruption leads to a rise in the stress hormone cortisol, which in turn promotes insulin resistance, pushing the body toward diabetes.

Moreover, some night shift workers consume sugary snacks to keep them awake through the night, and this increases the chances of developing diabetes.

Possible link to some cancers

The International Agency for Research on Cancer, part of the World Health Organization, has classified night work as a probable carcinogen, citing evidence linking it to breast, prostate, and colorectal cancers.

This may be because disruption of the body's circadian rhythm alters the timing of melatonin production, a hormone believed to have tumor-suppressing properties, in addition to lower vitamin D due to lack of daylight, and the low-grade chronic inflammation caused by sleep disruption.

Is there a solution to these problems?

Researchers are currently studying the idea of splitting sleep into two periods during the day, rather than trying to sleep for one long period after the night shift. This pattern is known as biphasic sleep, where a person gets a morning sleep period and an afternoon one.

A study of workers in polar regions observed that many of them naturally slept in two periods: the first after returning from work in the morning, and the second in the afternoon before the next shift.

Researchers believe this pattern may be closer to the natural human sleep pattern before the spread of artificial lighting.

Researchers have noted that in earlier historical periods, humans often slept in two phases, waking for a short period in the middle of the night and then going back to sleep, before modern lighting changed sleep habits.

In addition, current studies are examining the benefit of naps for shift workers, and some results suggest that short sleep during or after work hours may reduce drowsiness and improve concentration, and may also help reduce the risk of driving while feeling fatigued after work.

Researchers emphasize that the goal is not to ask night workers to change the nature of their work, but to find more practical ways to help them cope with sleep disruption.