- A small study found that nurses working double shifts had higher cortisol levels, especially at midnight, than nurses working single shifts.
- That suggests longer shifts may disrupt the normal daily rhythm of cortisol and increase physiological strain.
- The study was small and only included female nurses, but the findings fit with wider concerns about prolonged working hours.
Researchers compared cortisol levels in 52 female nurses during single and double shifts.
Saliva samples were collected in the morning, after the shift and at midnight.
Cortisol normally follows a circadian pattern.
It tends to be highest in the morning and lowest around midnight.
That basic pattern was still visible in the study.
But the nurses working double shifts showed higher mean cortisol levels overall.
The midnight difference stood out most.
Cortisol was nearly twice as high at midnight in double-shift workers compared with those on single shifts.
That suggests prolonged shifts may put the body under greater physiological stress and interfere with its normal hormonal rhythm.
This matters because cortisol is not just a stress marker in the vague everyday sense.
It is part of the body’s core system for regulating alertness, metabolism and the response to strain.
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If that pattern is repeatedly disrupted, it may have knock-on effects for sleep, recovery and general health.
The study is small, and it cannot tell us how these cortisol changes play out over years.
It also only looked at female nurses, so the findings cannot automatically be generalised to everyone.
Even so, the result is not particularly surprising.
Long shifts are demanding, and the biology appears to reflect that.
