ALTERATIONS OF LIFESTYLE AND RISK OF CANCER
Several studies have revealed that there might be a
significant association between reiterative circadian clocks and the occurrence
of different types of cancer, especially breast and prostate cancer. Those
studies were mainly focused on individuals working on rotating night shifts
whose circadian cycles are more prone to disruption, e.g. aviators, airline
stewards, and whatnot1.
incidence rates of breast cancer are reported in night shift female workers.
Further, risk of developing breast cancer is markedly increased in women
working more often on the night shift2. Melatonin is believed to
have an important role in inhibition of tumorigenesis (i.e. cancer growth)3.
This feature of melatonin, however, is circadian clock-dependent. Individuals
who often participate in night shifts are exposed to higher levels of
artificial light4. Exposure to light has been proposed as having
suppressive properties that lower melatonin levels, increasing the likelihood
of developing certain cancers in those night workers1,3. This
explanation has been found to be reflected on a number of observational designs’
results. A pilot study conducted among Indian menopausal women indicated that
visually challenged menopausal women had a conspicuously lower risk of
developing breast cancer in comparison with another similarly-aged group of
sighted women5. If this hypothesis holds true, then it can be
speculated that the risk of developing breast cancer is inversely associated
with grade of visual impairment1, 5. Another study showed a
notably increased risk of endometrial cancer in women who had exceeded 20 years
of rotating night-shift work6. Another concern is that obesity is
associated with higher odds of developing endometrial cancer7.
Prostate cancer and acute myeloid leukemia
reported that prostate cancer and acute myeloid leukemia are prevalent among
male night-shift workers. A cohort study carried out among 2,740 Air Canada
pilots revealed that prostate cancer and acute myeloid leukemia incidence rates
were significantly increased upon observation8. As well, another
cohort study of Northern European pilots showed an increased relative risk of
prostate cancer in tandem with longer flight times9. Increased
risk of prostate cancer in rotating-shift workers was also reported by a cohort
study conducted among 14,052 male workers in Japan10.