Thursday, July 4, 2013

The Hazards of Working Nights: for breasts and beyond

The jury is still out whether Angelina's choice is brave or fearful, but the fact remains: having or not having the "bad" genes is not enough to develop or avoid developing breast cancer. As a matter of fact, only 5% to 10% of breast cancer cases result directly from inherited gene defects. Check it yourself, by using this decision tool developed in Stanford.  Even though for members of some families with BRCA mutations the risk may be as high as 80%, this could be because of environmental exposures and behavioral habits "running in the family". What are they?

Among the controllable risk factors are hormone therapy, birth control pills, drugs (like DES discontinued in the 70s), the use of alcohol (if 2 or more drinks per day), heavy smoking since early age, gaining weight after menopause, exercising less than 1-2 hours per week,  certain cosmetics and personal care products, pesticides (such as DDE), PCBs (polychlorinated biphenyls) and other environmental exposures.

One of such exposures is working at night. And Kristan Aronson's team from Queen's University showed that the risk is not limited to nurses, as in most previous studies.

The study examined over 1000 breast cancer cases vs about the same number of healthy cases, matched by age in Vancouver, British Columbia and Kingston, Ontario.  It found that breast cancer risk was twice higher with 30-plus years of night-shift work versus people that did not have night-shift jobs. The risk is more than three times higher for those working at nights in the health care field. But people working at nights or having rotating schedules for shorter duration of time seem to be unaffected.

Why would staying awake after dark for many years be hazardous to health? Perhaps because of the lack of Melatonin. This hormone is produced naturally by our brains when lights go out, to make us less alert and prepare us for sleep. The more daylight exposure versus night time darkness, the better. Melatonin might help the body in many different ways - for example, by downregulating some of the hormones influencing tumor growth or by exhibiting anti-oxidant and immuno-enhancing properties.
Night shifts are also associated with increased stress and a plethora of health conditions as seen from the number of sick leaves people take, periodontal index (measure of oral health), glucose tolerance, number of heart attacks and strokes, cases of IBS and internal cancers. Actually, night time work was shown to increase the risk of cancers even more than exposure to exhaust fumes.

But this is all statistics. Individual cases can certainly break the mold. Yet, it's summer, so let's make the most of natural light.


Grundy A, Richardson H, Burstyn I, Lohrisch C, Sengupta SK, Lai AS, Lee D, Spinelli JJ, & Aronson KJ (2013). Increased risk of breast cancer associated with long-term shift work in Canada. Occupational and environmental medicine PMID: 23817841

Hansen J, Lassen CF Nested case-control study of night shift work and breast cancer risk among women in the Danish military Occup Environ Med 2012; DOI: 10.1136/oemed-2011-100240.

M S Wolff and A Weston. Breast cancer risk and environmental exposures. Environ Health Perspect. 1997 June; 105(Suppl 4): 891–896. PMCID: PMC1470027

Madigan MP, Ziegler RG, Benichou J, Byrne C, Hoover RN. Proportion of breast cancer cases in the United States explained by well-established risk factors. J Natl Cancer Inst. 1995 Nov 15;87(22):1681–1685.


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