Outline and evaluate the consequences of disrupting biological rhythms

Criticisms of the research on jet lag include issues with establishing cause and effect. Stewart and Amir (1998) found that rats who have been emotionally upset are less effective at resetting their innate body clocks using light as a zeitgeber compared to rats which have not been emotionally upset. Some humans find flying stressful and the fear of flying is a common phobia. The suggestion here is that the stress of flying could be the cause of the symptoms associated with jet lag rather than travelling through several time zones. Rats have been found to have similar DNA to humans and many drugs have been tested on rats first before human trails therefore animal research may be reliable but there are still issues with how much we can extrapolate from animal research and to what degree it can be applied to humans.  Research by Stewart and Amir is however supported by studies on flight attendants by Cho et al (2000) which found that regular, long-haul aircrew had raised levels of the stress hormone cortisol and performed less well than control participants on memory tests. A follow-up study in 2001 showed that more experienced female aircrew did not do as well on reaction time and memory tests than less experienced aircrew; again indicating the negative effects of cortisol on the hippocampus. Although the studies by Cho et al support the stress, the studies do not identify what is causing the stress, whether it is the flying itself or the occupation. Also individual differences such as the predisposition to stress have not been accounted and it could be that the release of the stress hormone cortisol was a result of the anxiety of taking the tests.

Shift work also affects the sleep-wake cycle and there are two types; fluctuating and non-fluctuating. Fluctuating shift work is when there is a regular change in shift work hours however, non-fluctuating shift work is constant and therefore resynchronisation of the internal body clock takes time but the body can adjust and adapt to this.  Shift workers have been found to have higher rates of heart disease, cancers, and diseases of the digestive system. Knutsson et al (1986) found that those who worked shifts for 15 years or more were three times more likely to develop heart disease. Shift work is also associated with a higher propensity for mental health problems such as stress, anxiety and depression. They can also suffer sleep loss, reduced REM and stage 2 sleep as well as general fatigue and even reduced brain volume. Research by Boivin et al (1996) found that night works experienced a circadian ‘trough’ which caused a decrease in alertness which resulted in poor decision making. They also found that shift workers who have to sleep during the day have a poorer quality of sleep due to interruptions such as noise and light. Czeisler et al are the main researchers into shit work and its effects. They conducted a study in 1982 on a group of shift workers following a backwards rotating shift system who had previously reported a range of health problems. They discovered that it takes about 16 days to adjust to a new shift pattern and so proposed that the shift rotation period be changed from 7 to 21 days. They recommended that shifts should rotate forwards in time (phase delay) taking advantage of the body’s natural preference for a slightly longer than 24 hour cycle. The results of the changes were significant as workers reported liking the new shift schedules and enjoying better health; they also made much more productive use of their leisure time when not working. The changes were also positive for employers since there was an increase in productivity and decrease in errors that led to accidents. Criticisms of this research by Czeisler et al is that the works may have improved in productivity due to social facilitation and may have been exhibiting demand characteristics as they may have felt pressure to work better whilst being observed. Thus the results of the study may not be completely valid.