Biological rhythms are controlled by endogenous pacemakers, which are our internal biological clocks and these rhythms are also affected by exogenous zeitgebers, for example light, food and noise. The most common disruptions of our biological rhythms occur due to aeroplane travel, which results in jet lag, and also due to shift work, resulting in shift lag. (AO1)
Shift work described a type of job in which individuals have to be alert at night when they work, and they sleep during the day. This results in reduced quality of sleep because it goes against our natural biological rhythms as daytime sleep can be interrupted due to exogenous zeitgebers such as light and outside noise. (AO1)
One of the effects of shift lag has been found to be decreased alertness. Shift workers often experience a circadian trough where there alert levels plummet. This usually occurs between 12.00am and 4.00am and is due to reduced body temperature and a decrease in cortisol levels. (AO1) This predicted effect of shift work has been supported by research by Moor Ede. It has been found that the decreased alertness as a result of shift lag costs the USA $70 billion per year. More evidence comes from the 3 Mile Island nuclear power station disaster, which occurred at around 4am, and similarly the Exon Val Dez oil tanker accident occurred at 12am and resulted in the spillage of oil in the oceans affecting thousands of wildlife. (AO2)
A second effect of shift work is believed to be the increased risk of organ disease that is associated with the number of years spent doing shift work. (AO1) Knutsson et al provided supporting evidence for this, as it was found that those who spent 15 years or more doing shift work had an increased risk of developing heart disease. (AO2)
A third and final effect of shift work is sleep deprivation. It has been suggested that sleeping during the day is less effective than at night due to more...