Jet lag occurs when normal circadian rhythms are disrupted by travelling across time zones. When we cross time zones there is a shift in zeitgebers, which causes a conflict between external cues and endogenous circadian clocks.
- Generally eastward flights (where there has been a phase advance of the circadian rhythm, ie. backward shift in the 24 hour cycle) cause greater problems than travelling west (where there is a phase delay, i.e. a forward shift in the 24 hour cycle.)
- Jet lag is less of a problem when travelling west because the body finds it less difficult adjusting to a slightly longer day than to a slighty shorter one.
- One of the main after effects of jet lag is disturbed sleep, with problems going to sleep after eastward travel and problems with premature waking, having travelled west.
- A general rule of thumb is that, fo each time zone passed, one day is needed.
- Even though the SCN can readjust its clock within the day, the effects of jet lag can last up to a month because internal clocks entrain at different speeds.
- This means that the central and peripheral clocks remain uncoordinated for some time.
Jet Lag and Sport.
- Reported on the performance of the soviet union volleyball team after travelling the plan in japan. The team lost matches the first three days, but won by increasing margins over the next six.
- Sasaki said this was due to the re-entrainment of the soviet team to the japanese time zone.
- This research (and most sporting research) overlook the influence on that of the team and varying quality of the opposition.
- Also, there was no baseline score for comparison.
- Therefore the conclusions drawn by such studies are unreliable.
Jet Lag and Sport.
Recht et al (1995)
- looked at the effects of jet lag on the performance of baseball teams.
- They studies three complete season records of 19 northern american teams.
- They found that home teams won 56% of the games, but the chances of winning depended on wether the visiting teams had travelled eastward.
- The researchers found no such advantage when the visiting team had travelled westward.
HOWEVER...Studies like these have many flaws.
1. They suffer from problems with the selection of data for analysis; there is a lack of control over the behaviour of team members en route which may affect perforance, for example, alchohol consumption, amount of rest etc.
2. They tend to overlook the significant impact on team performance of non-playing individuals, like coaches.
Jet lag and Sport (Cont.)
O'Conner et al (1991)
- looked at the effects of travelling across for time zones on competitive swimmers.
- They could find no significant evidence of a drop in performance that could not be put down to a lack of training due to travel.
Lemmer et al (2002)
- Investigated the performance of 13 althletes who had travelled westward over 6 time zones and 6 who had travelled eastward over 8 time zones.
- They found that training peformance of all athletes was disturbed by jet lag on the first day after arrival, with jet like symptoms persisting until day 6 for the westward group and day 7 for the eastward.
- They found training performance was wost in the first 4 days for the westward group.
- Although they did suggest that this may be due to the relatively small sample in the eastward group making the data especially vunerable to individual differences.
Jet Lag and Cancer.
Rafnsson et al (2001)
- Used data gathered from 1500 flight attendants.
- They found that those who had been flying for over 5 yeards had double the risk of breast cancer.
HOWEVER.. a number of explanations have been proposed for the relationship between jet lag and cancer, including the effects of regularly working at high altitude, flight dehydration and greater exposure to cosmic radiation and magnetic feilds.
Kojo et al (2005)
- found no increase in risk of beast cancer among cabin crew that could not be attributed to established risk factors, such as family history of cancer.
- in there stidy there was no clear evidence of disruption to circadian rhythms due to jet lag was linked to breast cancer.
Jet lag and Cancer (Animal research and Melatonin?
Filipski et al (2004)
- Provides a potential animal model for the relationship between jet lag and cancer.
- They re-created the effects of chronic jet lag in mice by repeatedly phase advancing the light dark cycle by eight hours every two days.
- They found that the desynchronised animals experienced accelerated cancer tumour growth and suggested that thisacceleration was causedby uncoordinated central and peripheral circadian clocks.
MELATONIN AND LIGHT.
Gauger and Sancar (2005)
- Suggest that it is the role of light rather than ryhtym disturbance itself which causes cancer.
- Light produces a reduction in melatonin level , and it is these low levels of melatonin that are linked to development of cancer.
Jet lag and Cortisol.
Cho (2001) said that constantravel across time zones has been found to increase the amount of the stress hormone cortisol in the body.
- Pp's in his study were 20 healthy women aged 20-28 employed by international airline companies for 5 years.
- Half the women had ashort jet lag recovery period of less than five days bewteen transmeridian flights that crossed seven time zones.
- The other half were a long recovery group that had 14 days between transmeridian flights, during which time their flighs were short and did not involve large time shifts.
- MRI scans were used to assess brain structure, and researchers tested pp's with psychological tests of cognitive functioning.
- He found that the shorter recovery group had noticably smaller temporal lobes ad scored lower on visuo-spatial tests.
One important implication of this research is that the temporal lobe atrophy associated with prolonged jet lag might be reduced by introducing periods of et leg recovery.