Night Work May Shift PSA Level Higher

25% of US Is Not on a Regular 9 to 5

Nick Mulcahy

August 22, 2013

Men engaged in shift work, including working at night or on a rotating schedule, had an increased likelihood of having an elevated prostate-specific antigen (PSA) value, according to new American research.

Specifically, there was a statistically significant association between current shift work and an elevated PSA of 4.0 ng/mL or greater. The study is based on data from the National Health and Nutrition Examination Survey (NHANES).

"Our findings are consistent with prior reports that suggest shiftwork is a risk factor for prostate cancer and extend these findings by demonstrating that PSA level is elevated among shiftworkers compared to nonshiftworkers," write the authors, led by Erin Flynn-Evans, PhD, of the Brigham and Women's Hospital in Boston, Massachusetts.

The study was published online August 13 in the Journal of the National Cancer Institute.

The authors acknowledge that the study may be a red herring because shift work might be a risk factor for prostatitis or benign prostatic hyperplasia, the 2 other conditions associated with elevated PSA.

However, there is enough evidence tying shift work and cancer that the World Health Organization categorized shift work (with circadian disruption) as a "probable carcinogen," the authors point out.

Indeed, men working at night had approximately double the risk of those who did not work the nightshift for a variety of malignancies, including prostate cancer, according to a 2012 Canadian case-control study. Much of the previous work on the link between cancer and nightshifts has focused on breast cancer; there has even been compensation awarded to flight attendants in Europe. Recently, a study demonstrated a possible link between nightshift work and ovarian cancer.

Approximately 25% of the US population either punches the clock at night or is on rotating shifts; so this issue, including its possible relation to developing prostate cancer, deserves research, the current study authors say.

The new study prompted a pair of experts to muse about a "more precise and holistic approach to prostate cancer screening" in an accompanying editorial.

Age, race, and family history are in need of supplementation as predictive factors, write Eric Singer, MD, and Robert DiPaola, MD, of the Rutgers Cancer Institute of New Jersey in New Brunswick.

The pair say that if other research confirmed the link between shift work and PSA level as well as prostate cancer, then circadian rhythms could join other potential risk factors such as lifestyle (eg, exercise), nutrition (eg, diet content and caloric intake), and other medical conditions in a "more nuanced" predictive nomogram.

In the meantime, the new study has "again reminded us that we do not fully understand many of the components that may influence a man's PSA level," they write.

Two and a Half Times the Risk

NHANES, which provides a representative sample of adult, noninstitutionalized American men, is a "unique vehicle" for the new study, say the editorialists, because both occupational and PSA information are available for analysis.

The study authors accessed 3 years of data (ranging from 2005 - 2010 surveys) and found a total of 2017 men (aged 40 - 65 years) having a current PSA test result and no history of cancer.

Out of that group, which included a mix of men working regular jobs and those doing shift work, 3% of the men had a total PSA level of 4.0 ng/mL or greater.

A PSA result of 4.0 ng/mL or greater was considered elevated because this value has historically been used as the clinical threshold for screening, explain the authors.

The age-adjusted odds ratio for having a total PSA result of 4.0 ng/mL or greater among shift workers compared with non–shift workers was 2.48 (95% confidence interval [CI] = 1.08 - 5.70; P = .03).

However, the researchers did a further analysis because there were some differences between the group of shift workers and the group of non–shift workers, including health insurance coverage.

When they analyzed the data in a multivariable model (adjusted for age, body mass index, race/ethnicity, health insurance, average hours of sleep per night, and months on the current job), the odds ratio increased slightly to 2.62 [95% CI = 1.16 - 5.95; P = .02]).

The study was supported by a postdoctoral fellowship from the Harvard Medical School Division of Sleep Medicine Training Program in Sleep, Circadian and Respiratory Neurobiology. The authors and editorialists have disclosed no relevant financial relationships.

J Natl Cancer Inst. Published online August 13, 2013. Abstract, Editorial

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