The causes of prostate cancer are hormone-dependent, just like breast cancer. While male and female hormones are crucial to prostate and breast cancer development respectively, female hormones also play a role in prostate cancer while male hormones also play a role in breast cancer.
Both cancers are also impacted by another hormone called melatonin, which is linked with the sleep-wakefulness cycle. A link between breast cancer in women and night shift work has been established. Working at night exposes women to light when they should be asleep in the dark. It is also believed that men working night shifts and exposed to “light pollution” may increase the risk of contracting prostate cancer.
At night, the body’s internal clock says it should be dark. But when exposed to light at night, the brain produces less melatonin. Melatonin serves a critical function in suppressing cancer formation in other organs at the gene level.
Melatonin ins produced in a tiny body located at the brain’s centre called the pineal gland. A grain-size group of neurons in the brain which serves as our internal clock tells the pineal gland to produce melatonin. This internal clock is reset by natural light outside that we encounter every morning on waking up.
This internal clock serves as our body’s chief biological pacemaker, synchonizing all our internal biorhythms, even at tissue and cellular levels, to a 24-hour circadian cycle. We human beings are active during the day and are programmed to sleep at night. Our bodily functions are timed so that the most important biorhythms such as alertness, metabolism and performance are optimal during the day, while sleep is optimal at night. DNA synthesis, healing, recovery and renewal occurs mainly at night.
The resetting of the internal clock takes place every morning when one wakes up and the eyes perceive natural sunlight outside. This natural light is the cue the pacemaker needs to tell the pineal gland to pace itself so it produces the most melatonin at night.
However, if the pineal gland is routinely stimulated by light at night, it might be tricked into turning down or even switching off its melatonin production. When this happens, all our bio-rhythms including those of our sex hormone levels and genes known to be controlled by circadian rhythms, become unregulated.
Over years of shift work, his kind of pacemaker resetting throws cellular biorhythms into disarray. In this way, the prostate in men and breasts in women may become more susceptible to cancer development. A link between light pollution and lymphoma has also been observed.
About 10% of genes are directly subject to this chief pacemaker’s oversight. These circadian genes help to suppress cancer formation. In particular, the Per1 gene is known to inhibit the growth of prostate cancer cells. When the functioning of such genes is disrupted by light pollution, the bio-rhythms of sex hormone levels may also go awry. This may affect some other circadian genes as well. This could in turn cause prostate cancer.
Recent epidemiological studies in Japan and the United States suggest that workers who have to rotate shifts face a higher risk of prostate cancer compared to those who have day shifts only or night shifts only. In March 2009, the Danish government agreed to compensate 40 female nurses and flight attendants with breast cancer who had worked a night shift at least once a week for 20 years. It may be a matter of time that prostate cancer sufferers who have worked night shifts for years will also be eligible for compensation.