Irregular work hours cause ill-health. The effects on men and women are different.

Shift-work and irregular work schedules can cause several health-related issues and affect our defense against infection, according to new research.

These health-related issues occur because the body’s natural clock, called the circadian clock, can be disrupted by inconsistent changes in the sleep-wake schedule and feeding patterns. To study this the researchers developed a mathematical model to look at how a disruption in the circadian clock affects the immune system in fighting off illness.

What the researchers say: “Because our immune system is affected by the circadian clock, our ability to mount an immune response changes during the day,” said the lead researcher. “How likely are you to fight off an infection that occurs in the morning rather than midday? The answer depends on whether you are a man or a woman, and whether you have an irregular work schedule.”

The researchers created new computational models, separately for men and women, which simulate the interplay between the circadian clock and the immune system. The model is composed of the core clock genes, their related proteins, and the regulatory mechanism of pro- and anti-inflammatory mediators. By adjusting the clock, the models can simulate male and female shift-workers.

The results of these computer simulations show that the immune response varies with the time of infection. Model simulation suggests that the time before we go to bed is the “worst” time to get an infection. That is the period of the day when our body is least prepared to produce the pro- and anti-inflammatory mediators needed during an infection. Just as importantly, an individual’s sex impacts the severity of the infection.

“Shift work likely affects men and women differently,” said the co-author. “Compared to females, the immune system in males is more prone to overactivation, which can increase their chances of sepsis following an ill-timed infection.”

So, what? Many of us are forced to work irregular hours—or fly internationally over time zones for business. What the researchers show here is that these activities over-stress our design-specs—like so many aspects of the way we live and work and this causes all sorts of problems with our immune system.

And this is hardly the first study that has come to this conclusion. Ongoing irregular sleep has been shown by previous research to be potentially deadly. Research reported in the NYT this week has shown that too little sleep in middle age is a contributory cause of dementia.

That the irregular hours impact men and women differently is also not surprising. The same sort of differences have been seen in the way the genders are predisposed to certain physical and mental maladies and to their tolerance levels for different stressors.