Changes in the diurnal rhythms of cortisol, melatonin, and testosterone after 2, 4, and 7 consecutive night shifts in male police officers.
Level 3 - non-randomized controlled study
Within-subject repeated-measures field study without stated randomization of condition order
PubMed 27715321 · doi:10.1080/07420528.2016.1212869
What was done
Researchers evaluated the impact of consecutive night shifts on diurnal hormone rhythms in 73 male police officers across five police districts. Participants completed three intervention schedules: two night shifts followed by two recovery days (2+2), four night shifts followed by four recovery days (4+4), and seven night shifts followed by seven recovery days (7+7). Saliva samples were collected every 4 hours while awake on the final night shift day and the final recovery day of each block to measure melatonin, cortisol, and testosterone rhythms.
What was found
Increasing numbers of consecutive night shifts altered endocrine rhythms differently. Melatonin diurnal amplitude was suppressed by 4.9% per day (95% CI 1.4% to 8.2% per day; p = 0.006). Cortisol diurnal phase delayed by 33 minutes per day (95% CI 18 to 48 minutes per day; p <= 0.001) without changes in amplitude. Testosterone rhythm showed no effect from the number of consecutive night shifts and completely followed the sleep/wake cycle. After 2, 4, and 7 recovery days, there were no differences in the rhythms of melatonin, cortisol, or testosterone.
Why it matters
This field study demonstrates that successive night shifts cause progressive, hormone-specific circadian desynchronization, with melatonin dampening and cortisol phase delaying, while recovery periods matching shift duration appear sufficient to reset baseline diurnal rhythms.
Limits
The cohort was exclusively male police officers, limiting generalizability to female workers or other occupations. Saliva was collected only during waking hours, leaving sleep-period hormone profiles unmonitored. The abstract does not specify whether the order of shift conditions was randomized, and clinical health outcomes were not evaluated.
Cited by
- supports At around 10:30 to 11:30 PM, circulating levels of estrogen, testosterone, progesterone, adrenaline, and cortisol are low while melatonin levels are high.