Study reignites controversy over cancer risk of shift work

A Danish study recently published in the European Journal of Cancer will add new fuel to the controversy around the health impacts of shift work.

Published in August, the study by researchers Johnni Hansen and Richard G. Stevens suggests nurses who work rotating shifts after midnight have a significant increased risk of breast cancer compared to those who work only on day shifts.

This is not the first such study to make the link.

Thirty-seven Danish women had received compensation in 2009 after claiming their breast cancer was linked to their long-term night shift work.

The Canadian Cancer Society suggests researchers are looking at a number of probable causes, including the following:

  • Lower exposure to daylight may decrease the body’s production of vitamin D, or change the body’s production of hormones;
  • Disruption of sleep patterns can change the body’s natural rhythms or affect the production of chemicals;
  • Lifestyle risks associated with shift work include smoking, alcohol use, an unhealthy diet and a lack of exercise.

The most recent Danish study includes one of the largest sample sizes, looking at a group of 58,091 female nurses who were alive on July 1st, 2001, free of breast cancer, and born between 1933 and 1970. Of that group, 310 cases of breast cancer were confirmed between July 2001 and June 2003.

The sample size of this study overcame criticism levelled at previous studies, questioned for having too small numbers of cancers in their study groups to be conclusive.

What was new about the Danish study was the analysis of risk according to different shift systems, including permanent night shifts.

“Evening work is less disruptive for circadian biology than night work,” the study states. “but rotating shifts between day and night may be more disruptive.”

The authors of the study also noted an increase in breast cancer risk even after a relatively short period of night-shift work.

The Canadian Cancer society suggest that workers doing night shifts should make healthy lifestyle choices that include eating well, being active, maintaining a healthy body weight, not smoking, limiting alcohol consumption and getting enough vitamin D.

They also recommend that night shift workers have regular cancer screening and speak with their doctor about what other preventative measures may be right for them.

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