ReviewHealth in a 24-h society
Section snippets
Time-of-day influences
More than a century ago, it was reported that the capacity for doing mental work varies throughout the day. Several empirical studies have revealed time of day variations in performance, with subtle differences between different tasks.8 Similarly, in participants that are exposed to 36–60 h of sustained wakefulness in controlled laboratory (or constant routine) conditions, significant time of day variations in task performance are reported, with performance being worst for all tasks just after
Shiftwork and jetlag
A key characteristic of the biological clock is its ability to re-adjust (either by phase advancing or delaying) to changes in the environment, for example after transmeridian travel. On average, the clock shifts about 1 h per day in the absence of countermeasures.26 Symptoms of jetlag are thought to be caused by desynchronisation of circadian rhythms from the external environment, the transient change in the phase relationship of individual rhythms,26 and perhaps changes in the amplitude of
Sleep loss and sleepiness
Sleep loss is obviously the most important immediate consequence of night work. In general, sleep loss will result in performance deficits, including increased variability in performance, slowed physical and mental reaction time, increased errors, decreased vigilance, impaired memory, and reduced motivation and laxity.39 There is no consensus on the extent of impairment resulting from a given amount of sleep loss.
Depending on the performance task measured, after 17–19 h of sustained
Legal implications of 24-h operations
Accidents associated with sleepiness can lead to legal proceedings, for example, charges of culpable driving. In a recent case in the USA, the family of a woman killed in a road accident after a tractor-trailer hit the back of her vehicle received a US$24 million settlement from the driver's employer. The plaintiffs alleged that the employer's violation of hours of work regulations resulted in driver fatigue, which caused the collision.49
According to common law principles, actions done while
Conclusions
Enormous progress has been made in our understanding of circadian rhythms and our ability to manipulate them. Endogenous periodicity is an inherited characteristic for which several candidate genes have been identified. Human tolerance to shiftwork and transmeridian travel could be associated with endogenous periodicity, and thus, changing the design of shift schedules, and giving specific advice to individual workers could help to improve their health and reduce risk factors for major disease.
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