Can This Job Give You Cancer?

Can This Job Give You Cancer? about undefined

A study conducted at the Centre for Research in Epidemiology and Population Health in France suggests that certain types of jobs might actually contribute to cancer development. And they were not referring to jobs that involve exposure to toxic chemicals.

Were they talking about jobs that cause too much stress, or that make the worker unhappy for some other reason? Not necessarily! This type of job can cause cancer even if you love your work.

Here’s what they found. . .

Findings from this investigation, also called the CECILE study and published in the International Journal of Cancer (IJC), examined the role of night work in a large population-based, case-control study. The study aimed to identify environmental and genetic factors that might play a role in breast cancer.

The French researchers specifically focused on the type of night work, its duration and frequency in relation to developing breast cancer. They also examined the role of night work in the period before a woman’s first full-term pregnancy as a possible window of exposure.

And if you’re thinking, “I don’t do night work, this doesn’t apply to me” – keep reading. There’s cancer-preventing news here that all of us need to know.

The dangers of night work  

The investigators examined lifetime job history and work schedules of each night work period for 1,232 breast cancer patients and 1,317 control subjects. The participants answered questions during in-person interviews by trained interviewers who collected information on:

  • Demographic and socioeconomic characteristics
  • Diet
  • Family history of cancer
  • Lifestyle factors
  • Medical history
  • Occupational history
  • Reproduction
  • Residential history

The researchers also collected blood samples from participants during their interviews.

When they looked at the participants’ job histories, they documented work task descriptions… specific work places… occupational exposures… and work schedules.

The women were asked whether they had worked for at least one hour between 11:00 at night and 5:00 in the morning during all or part of each job. The investigators also documented any night work period according to the month and year, number of nights per week, and the hour when the night shift started and ended.

When they analyzed the data, the investigators determined that the night shift workers suffered…

A 30 percent higher risk of breast cancer  

Researchers found the risk of developing breast cancer was 30 percent higher in women who had worked nights compared to women who had never worked nights!

The risk increased in women who worked nights for more than four years. They also found an increased risk in women who worked less than three nights per week, because this produced more frequent disturbances between night and day rhythms.

The investigators found the association with breast cancer was even stronger in female night workers who worked prior to a first pregnancy. They suspect this could be because mammary cells that are not completely differentiated in women before their first pregnancy are more vulnerable.

According to Pascal Guenel, lead study author, the finding “corroborated the results of previous studies and poses the problem of taking night work into consideration in public health management, especially since the number of women working atypical hours is on the increase.”

Presumably he was talking about France. I don’t know whether night work is becoming more common in North America.

Although a few prior studies demonstrate the link between night work and breast cancer, the IJC article cites several cohort studies of night shift nurses that provide more consistent results than general-population-based studies.

In a nutshell, these studies show that night work is more disruptive to your circadian rhythms. These rhythms are like a biological clock tracking your physical, mental, and behavioral changes in a 24-hour cycle.

A good night’s sleep can be your
most important secret of good health 

As the editor and publisher of books and newsletters not only on cancer but on Alzheimer’s and memory as well, I have a growing respect for how important it is to get from seven to eight hours of good sleep every night.

The evidence is overwhelming that poor sleep habits are a heavy blow against your health, and it’s not merely people on the night shift who are messing with their circadian rhythms.

Far too many of us are exposed to light all night long instead of sleeping in a quiet room that’s completely dark. If you’re exposed to even a low-level light like a night light, or like a street light shining into your room, then you’re leaving yourself open to much the same risk the French study uncovered. And it’s linked to far more health problems than breast cancer.

Who needs a clock? Your body has one of its own 

Your circadian rhythms control a wide variety of biological functions—and can be thrown out of whack in night workers or other people with disrupted hours – such as people who stay up late watching television or working on the computer.

The unnatural disruptions throw off your sleep-wake cycles… hormone release… body temperature… and other critical bodily functions.

Why is this? Although circadian rhythms are produced by natural factors in your body, they are also affected by environmental signals. Light is the main trigger influencing circadian rhythms, turning on or off the genes that control your internal clocks.

Abnormal circadian rhythms have been associated with sleep apnea and insomnia, obesity, diabetes, depression, bipolar disorder, and seasonal affective disorder (SAD).

With so many health problems linked to such an important biological clock, it’s clear to see why the International Agency for Research on Cancer (IARC) classifies work that disturbs the circadian rhythms as being “probably carcinogenic.”

Scientists have proposed several explanations for the observed links between night work and breast cancer:

  • Exposure to light at night eliminates the nighttime melatonin surge and its cancer-preventing benefits
  • Abnormal hours promote malfunction of genes that control cell growth and are themselves controlled by a daily cycle of some kind
  • Sleep disorders can weaken the immune system

The investigators say more research is needed to fully establish these connections. But it may be worthwhile to find out what makes your biological clock tick—and preserve your good health!

Best regards,

Lee Euler,


  1. Guenel, P et al. Night work and breast cancer: A population-based case-control study in France (the CECILE study). International Journal of Cancer, 2012; DOI: 10.1002/ijc.27669.
  2. Hansen J, Stevens RG. Case-control study of shift-work and breast cancer risk in Danish nurses: impact of shift systems. Eur J Cancer 2011.
  3. INSERM (Institut national de la santé et de la recherche médicale). “Night work may put women’s health at risk.” ScienceDaily. ScienceDaily, 19 June 2012. Available at .
  4. Lie JA, Roessink J, Kjaerheim K. Breast cancer and night work among Norwegian nurses. Cancer Causes Control 2006; 17: 39–44.
  5. National Institute of General Medical Sciences. 2014. Circadian rhythms fact sheet. Available at
  6. Pesch B, Harth V, Rabstein S, et al. Night work and breast cancer—results from the German GENICA study. Scand J Work Environ Health 2008; 36: 134–41.

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