Consequences of disrupting biological rhythms
Biological rhythms are driven by endogenous pacemakers (oscillators). Some of these oscillators are easily reset by exogenous zeitgebers (such as daylight, mealtimes and so on) whereas other oscillators are more resistant. The result is desynchronisation. The two most common examples of the disruption of biological rhythms and the resultant desynchronisation are shift work and aeroplane travel – resulting in shift lag and jet lag.
Phase advance and phase delay
The notion of phase advance and phase delay applies to all circadian disruptions, including both shift work and jet lag as well as simply staying up late and/or getting up early. In terms of jet lag, most travellers report less difficulty in adjusting when they are flying west (e.g. London to New York) than when they are flying east (e.g. New York to London). It probably because phase delay means that on the first morning you get up when your body is already quite awake – a bit like having a lie-in. On the other hand, with phase advance, you have to get up when you are in a circadian “through”.
The effects of circadian disruption vary considerably between individuals. It is possible that those people whose circadian rhythms change least are the ones who cope best overall. Reinberg et al. (1984) found that people who gave up shift work because they couldn’t cope tended to have rhythms that changed a lot while on shift, while the “happy shift workers” had unchanging rhythms.
Consequences of disruption
Shift work and shift lag
Night workers are required to be alert and so must sleep during the day, which is the reverse of our natural rhythms and out of line with most of the available cues from zeitgebers.
Decreased alertness- Night workers often experience a circadian “trough” of decreased alertness during their shifts (Boivin et al. 1996). This occurs between midnight, when cortisol levels are lowest, and 4.00 am, when core body temperature is at its lowest.
Sleep deprivation – Workers who have to sleep by day often experience sleep problems because when they finish work it is daytime and there are other interruptions e.g. noises outside and daylight reduces sleep quality. Daytime sleep is typically between one and two hours shorter than a nocturnal sleep period; REM in particular is affected (Tilley and Wilkinson, 1982). Poor quality daytime sleep then makes it even more difficult for shift workers to day awake through the night, especially when they hit the circadian trough.
Effects on health – There is a significant relationship between shift work and organ disease. For example Knutsson et al. (1986) found that individuals who worked shifts for more than 15 years were three times more likely to develop heart disease than non-shift workers. Martino et al. (2008) linked shift work to a range of organ diseases including kidney disease. This may be due to the direct effects of desynchronisation or indirect effects such as sleep disruption.
Jet Travel and Jet Lag
The term “jet…