Men who work a rotating shift
pattern may be at increased risk of prostate
cancer, research suggests.
Japanese scientists found
that staff working rotating shifts were four
times as likely to develop the disease as
those working day or night shifts.
But British experts said
the findings were far from conclusive.
The University of Occupational
and Environmental Health study, of more than
14,000 workers, features in the American Journal
of Epidemiology.
Shift work has also been
linked to an increased risk of breast and
bowel cancer.
The study also found that
night shift workers were at a slightly increased
risk of prostate cancer, compared with those
who only worked days.
The researchers suggest the
key may be reduced secretion of the hormone
melatonin, which the body uses to induce sleep.
Melatonin has also been shown
to have anti-cancer effects.
Reduced secretion of melatonin
has been linked to increased production of
sex hormones, which play a role in regulating
prostate tissues.
In normal circumstances,
secretion of the hormone is low during daytime,
increases soon after the onset of darkness,
peaks in the middle of the night, and gradually
falls until morning.
Not conclusive
Henry Scowcroft, of the charity
Cancer Research UK, said: "There have been
several previous reports that disturbances
to natural body rhythms might be linked to
cancer, and this report adds to that evidence.
"But it has never been shown
that the actual sleep disturbance itself is
responsible for the slight increase in risk
observed in these studies.
"It might be that people
with abnormal sleep patterns are more likely
to be doing something else, such as smoking
or eating unhealthily, that increases their
risk."
Mr Scowcroft said the researchers
only found 31 cases of prostate cancer over
10 years.
"There is a long way to go
before we can say for sure whether sleep disturbance
is linked to prostate cancer."
Chris Hiley, of the Prostate
Cancer Charity, said the research was interesting
- but not necessarily relevant to British
men.
"This research certainly
doesn't indicate that rotating shift patterns
mean it's more likely that you will die from
prostate cancer - the research paper doesn't
talk about an increased risk of dying at all.
"Neither does it say that
shift patterns cause prostate cancer.
"The researchers do speculate
about the possible role of melatonin in the
development of prostate cancer, but there's
nothing here that allows us to be confident
that a new important risk factor has been
identified.
"The researchers themselves
suggest more research is needed to see if
this finding occurs in other places to the
same or a greater degree - and only then,
if it does, might this translate into sound
advice to men."
