Research into shift-working doctors’ and nurses’ body clock response to light exposure highlights that there’s likely no ‘one size fits all’ answer to shift-work sleep disruption.

The Australian study of 21 nursing and medical staff in a Melbourne intensive care unit, published last week in The Journal of Physiology, indicates that the circadian body clock can be shifted by light exposure, potentially to align them with night shift patterns.

But the study – which measured the health professionals’ light exposure, their melatonin levels and noted their personal preference for mornings (lark) or evenings (owl) – also highlighted that a ‘one size fits all’ approach to managing sleep disruption in shift workers may not be appropriate.

Instead the author’s argue a personalised approach, with light-dark exposure scheduled and taking into account whether someone is a ‘morning’ or ‘evening’ person, could reduce the increased risk of health problems in shift workers.

Human’s sleep-wake cycle, is in part controlled by the circadian body clock,  that regulates all physical, mental and behavioural rhythms that follow a daily cycle. Light is the dominant environmental time cue for sleep patterns.

Night time shift work disrupts the normal sleep-wake cycle and our internal circadian rhythms, and has been associated with significant health problems, such as a higher risk of heart disease and cancer (1). Alertness levels are often markedly impaired while working night shifts.

Study leader, Prof Shantha Rajaratnam of Monash University and the CRC for Alertness, Safety and Productivity said it was known that night time shift workers were more likely to suffer health problems due to disruption of their circadian clock, and the mismatch between the timing of the clock and their sleep-wake cycle.

“This research is important because if we can realign a person’s clock to fit their shift pattern, then they will sleep better and this may result in improved health, safety and productivity.”

Such realignment is rare but in some circumstances, such as on offshore oil rig platforms, complete adaption has been observed in a 1998 study by Barnes et al.

The Melbourne ICU research aims to understand the relationship between light exposure and how an individual’s circadian rhythm was affected across a transition from day to night shift schedules.

The researchers found that timing of light exposure is the primary factor in determining how the brain clock responds to night shift work, accounting for 71% of the variability in timing of the clock observed in the study. It also found that the extent to which an individual is a ‘morning’ or ‘evening’ type affects how the body responds, which showed that a personalised approach is important.

This study was led by the CRC for Alertness, Safety and Productivity and the ICU nurses and doctors recruited into the study were working a schedule of day or evening shifts, or days off, followed by at least 3 or 4 consecutive night shifts.

Researchers measured the sleep-wake cycle responses to the shift schedule by monitoring the participants’ urinary concentration of the major metabolite of melatonin (6‐sulphatoxymelatonin) when they were on the day schedule, and at the end of the night shifts.

Melatonin is the hormone produced in the pineal gland known to be involved in the regulation of sleep cycles. Individual light exposure was measured using wrist actigraphs, worn for the duration of the study.

The study found substantial variability between individuals results.  Also that no participants met the criteria for having partially adapted to night work after three or four consecutive night shifts.

“These results will drive development of personalised approaches to improve sleep-wake cycles of shift workers and other vulnerable people, and could potentially reduce the increased risk of disease due to circadian disruption,” said the researchers.

The study abstract can be viewed here.

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