Shift work is increasingly regarded as
hazardous to sleep and health. Shift
work involves schedules that deviate from the standard, 9-5 daytime
workweek. Many people who work shifts are on rotating schedules that include
both days and nights, and others work consistently late nights, overnights, or
very early mornings. These schedules are frequently disruptive
to circadian rhythms, and make it difficult for people to get sufficient
amounts of high-quality sleep. Shift work is associated
with elevated risks for a number of serious diseases, including heart disease,
diabetes, and several types of cancer.
indicates that men who engage in shift work are at higher risk for PSA
(prostate-specific antigen), a protein that is produced by the prostate gland.
PSA tests are used to screen for prostate cancer and other prostate conditions.
Elevated levels of PSA are considered
an indicator of possible prostate cancer as well as several other non-cancerous
conditions, including prostatitis and enlarged prostate.
Researchers at Harvard University and the University of
the link between shift work and PSA levels. Researchers used data from the
National Health and Nutrition Examination Survey (NHANES), an ongoing national health study conducted by the
Centers for Disease Control. Researchers examined data from several NHANES
surveys conducted during the years 2005-2010, to create a group of 2017 men who
formed the basis for their inquiry. The men were between the ages 40-65, and
none had any prior history of cancer. (An exception was made for non-melanoma
skin cancer.) All the men had a current PSA test result. The group included a
combination of men working regular daytime schedules and men working shifts,
both overnight and rotating night and day shifts. Researchers’ analysis
revealed that men working shifts were significantly more likely to have
elevated PSA levels:
the group as a whole, 3% of men had PSA of 4.0 ng/mL or higher. “Normal”
PSA levels depend on several factors, including age—but PSA at or above
4.0 has traditionally been considered abnormal, and often leads to further
testing for prostate cancer.
who worked shifts were approximately 2.5 times as likely to have a PSA at
4.0 ng/mL or higher, compared to men who were engaged in non-shift work.
It’s important to note that this study did not examine the
risk of prostate cancer in relation to shift work, only the relationship of
shift work to PSA levels. An elevated
PSA is not itself a diagnosis of prostate cancer, and high PSA results can be
indicative of other, non-cancerous conditions. But an elevated PSA can
indicate the presence of prostate cancer. And other research has established
links between shift work and prostate cancer, as well as other cancers in both
men and women:
scientists studied the relationship
between shift work and several types of cancers. They found men who worked
night shifts had more than 2.5 times the risk for prostate cancer compared
to men who had never worked night shifts. Men working night shifts were
also at elevated risk for several other types of cancer, including cancers
of the pancreas, rectum, colon, bladder, and lungs. Several other cancers
showed no increased risk among night shift workers.
study in Japan of more than 14,000 workers found higher risk
of prostate cancer among men who worked night shifts compared to those who
studies have explored
links between shift work and breast cancer in women. One recent study found
that women who worked night shifts for 30 years or more had twice the risk
of developing breast cancer. Women who worked less than 30 years on night
shifts did not show an increased risk for developing breast cancer.
has also found night shift work linked on an increased risk of ovarian
cancer. This study found an increased risk for ovarian cancer among women
50 years and older who worked nights.
What is behind the cancer risks associated with shift work?
We don’t yet know, but several possible causes are being explored. Several of
these focus on the circadian disruptions associated with shift work, including
light at night, hormonal changes associated with
circadian disruptions, and the role of melatonin in tumor
The relationship of circadian dysfunction to cancer
risk is a critically important area of research. With millions of Americans
working shifts—and a wider array of jobs
requiring non-traditional schedules— this is an issue that needs rigorous study
Michael J. Breus, PhD
The Sleep Doctor®
Everything you do, you do better with a good night’s sleep™
twitter: @thesleepdoctor @sleepdrteam
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