Kubo et al
Study of 14,052 japanese workers, controlled for risk factors, four times more likely to develop cancer if working night shift
Schwartzbaum et al
compared incidence of cancer in occupational groups with at least 40% shift work with 30%. No relationship between shift work and cancer. Found no link between certain occupations and cancer risk.
Criticism of Schwartzbaum et al
Way it defined shift work and increased cancer risk. Combined different jobs with varying degrees of shift work, averaged out effect of high risk jobs/work schedules.
Possible explanation for increased cancer risk and shift work
Lowered melatonin secretion, which may have anti-cancer properties. Reduction in M causes increase in other hormones particularly oestradiol (oestrogen) responsible for growth of hormone sensitive cells in breast, associated ^ risk of bc.
support for melatonin
blind women have lower incidence of breast cancer
Spielgel and Sephton
Agree that increased risk cancer linked to shift work but as result of disruption to diurnal rhythms in hormone cortisol.
Recht et al
Effect of jet lag on north american/pacific time zone baseball teams. 3 complete seasons, travel over 3 time zones to play one another. Home team won 56% but chances of winning depend whether v traveled eastward. when traveled ew home team score 1.24 runs more.
Recht et al Criticism
Retrospective, have no control on teams behaviour which may affect results i.e. drinking, lack of sleep. overlook effects of non-playing members like coaches.
O'Connor et al (criticism of R&a)
Looked at performance of competitive swimmers, 4 time zones. Performance not impaired aside from that which could be due to lack of training travel.
Lemmer et al
performance of 13 athlete traveling ww over 6 time zones. Performance all athletes disturbed on 1st day. jl symptoms till d6 for ww and d7 for eastward.
Lemmer et al
performance worst for 1st four days for ww group may have been due to small ss vuln to ids. Lack of sufficient data overall.
Rafnsson et al
1,500 female flight attendants. After 5 years double risk of cancer.
support for rafnsson et al
studies also found link
criticism for rafnsson et al
not sure on cause. could be due to high altitude, flight dehydration, greater exposure cosmic radiation & magnetic fields as well as disturbed biological rhythms.
Kojo et al criticism rafnsson et al
found no increase in cancer which couldn't be linked to risk factors i.e. like family history.