The Grave Risks of Graveyard Shifts

Cancer risk in men may increase from night work

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) The brain releases a hormone to help with sleep when it’s dark called melatonin. But what happens with night workers? Is there danger in not generating any melatonin?

A recent study looked at male cancer patients with night jobs. Whether it’s related to melatonin or not, these researchers say the risk for certain cancers was higher in men with night jobs.

“This hormone (melatonin), habitually released in the middle of the night in response to absence of light, plays a pivotal role in hormonal functions and in the immune system,” said the study's author.

"Get plenty of sleep."

Marie-Élise Parent, PhD, professor of epidemiology and biostatistics at Institut national de recherché scientifique (INRS)-Institut Armand-Frappier at the Université de Québec, conducted the study.

Dr. Parent said, “Exposure to light at night can lead to a reduced production of the sleep hormone melatonin, inducing physiological changes that may provoke the development of tumors.”

For the study, 3,137 men were diagnosed with one of 11 different types of cancer between the ages of 35-70 from 1979-1985. Researchers looked for links between men with cancer and whether or not they had worked a night job. Researchers also evaluated 512 healthy men who did not have night jobs as a control group.

Investigations revealed these increased cancer risks among night workers, in terms of odds ratio. An odds ratio is the odds of one group getting a disease compared to the odds of the other group getting the disease, in this case any type of cancer. An odds ratio of greater than one means that the group had a greater chance of having the disease than the other.

Lung cancer and bladder cancer both had odds ratios greater than 1.5, while cancers of the colon, prostate, rectum, pancreas and non-Hodgkin's lymphoma all had odds ratios greater than two. This roughly means that night workers had about twice the risk of developing these cancers than non-night workers

Risks for stomach, kidney, esophageal and skin cancer were not found to be significantly different in night workers.

The length of the night shifts did not change the risk of cancer.

Further studies should evaluate the role of melatonin in cancer risk in studies including women, the researchers suggested.

This study was published in October in the American Journal of Epidemiology.

Funding for this study was provided by Health Canada. No conflicts of interest were reported.

Reviewed by: 
Review Date: 
November 11, 2012
Last Updated:
November 13, 2012