We've discussed before how night-shift workers are more prone to errors, which makes those workers more dangerous to you, but now it turns out, they may be even more dangerous to themselves. Studies consistently affirm the link between working all night and developing cancer, particularly breast cancer. Just last month,Occupational and Environmental Medicine published Danish research involving about 700 women who served in the military between the years 1964 and 1999.1 The study found a 40 percent higher rate of breast cancer among the women consistently working night-shift schedules. Those who put in three or more nights a week for six years or longer had more than double the rate of breast cancer compared to women who maintained normal schedules. Interestingly, the cancer risk was highest for those who considered themselves "morning people" -- who normally woke up early and felt brightest early in the day. Among that group, breast cancer rates were a whopping 400 percent higher than normal.
There's good news for women who work just occasional nights, because working one or two evenings a week doesn't seem to raise cancer risk much at all. But a surprisingly large group of workers exceeds that safe threshold. According to lead researcher Johnni Hansen, "About 10 to 20 percent of women in modern society have night-shift work. It might therefore be one of the largest occupational problems related to cancer."2
Earlier research came to similar conclusions. A 2001 Danish study of 7000 women concluded that six months of working the night-shift led to a 50 percent increase in breast cancer risk. Likewise, a 2006 Norwegian study involving 45,000 nurses found that those who worked the night-shift had double the incidence of breast cancer compared to their day-shift colleagues. These results led the World Health Organization to declare night-shift work "probably carcinogenic," and in response, the Danish government decided to compensate women who developed breast cancer after working night-shifts for longer than 20 years.
But as mentioned earlier, breast cancer isn't the only problem linked to working after twilight. A 2006 study found a 35 percent increased risk of colon cancer among night workers.3 And another 2006 study of 14,000 Japanese men found triple the rate of prostate cancer among men who worked rotating shifts.4 There's anecdotal evidence that there's a link to other cancers as well, although more research needs to be done to affirm this.
Then there are the other worrisome conditions linked to working night-shifts. Diabetes rates soar among those who work nights in comparison to their nine-to-five compatriots. A 2011 study found a 20 percent bump in Type 2 diabetes rates among nurses who worked nights for just three years.5Those who kept it up for 20 years had a 60 percent greater chance of developing the disease.
In fact, the rap sheet against the night-shift goes on and on, with lots of other sorry correlations affecting both mental and physical health. Clearly, playing with the normal daytime work schedule wreaks havoc with the body. But what causes the problems?
Scientists originally attributed the health problems to lack of sunshine, assuming that night-shift workers slept during the day so that they didn't get the requisite dose of vitamin D from the sun. But in fact, it turns out that those who work at night actually get more sun exposure than their peers do, apparently enjoying time outside in the afternoons. Scientists also suspected lack of exercise and poor eating choices, but in fact, there's little evidence that night workers have deficits in these departments. Reduced melatonin production was also a suspect since light shuts down melatonin production at night, but no clear connection was ever found.
Many experts now believe that the most likely cause of negative health impacts has to do with interrupted circadian rhythms. To test this theory, researchers from Harvard Medical School subjected volunteers to 28 days of constantly changing schedules.6 The scientists found that within just days, the subjects experienced significant increases in blood pressure, blood glucose, and insulin. They also had far higher levels of cortisol than normal. Cortisol is a hormone released during stress, capable of triggering various health disorders. The research highlights how disrupting body rhythms seems to throw off the system, although it doesn't exactly replicate the effects of years of a flip-flopped schedule.
Often, those who work the night-shift try to maintain a daytime schedule on their off-days, and this may actually exacerbate problems. According to endocrinologist Eve Van Couter, it might actually be healthier to completely switch to a permanent night schedule since every change in sleep and waking patterns seems to trigger biochemical shifts. Dr. Van Counter says that working consistent night-shift is "… better than shifting between day and night work constantly, but very few people want to always be a night worker."
What can you do if you're consigned to the graveyard shift or you have a rotating shift schedule? First, make sure you do eat well and exercise. Other than that, try to simulate a day and night contrast by making sure that at night, you work under full-spectrum, bright lights and, during the day, you rest in total darkness. Try to limit constant shift changes. If possible, constrict nights worked to two a week. Better yet, do what you can to get a daytime job. The double-time bump in income you get from working at night is ultimately too costly in terms of health.
1 Park, Alice. "Working the Night-shift May Boost Breast Cancer Risk." 29 May 2012. Time Healthland. 20 June 2012. < http://healthland.time.com/2012/05/29/working-the-night-shift-may-boost-breast-cancer-risk/>
2 "Night-shift Might Boost Women's Breast Cancer Risk: Study." 29 May 2012. Medline Plus. 21 June 2012. . < http://www.nlm.nih.gov/medlineplus/news/fullstory_125638.html>
3 Myers, Donna. "Working the Night-shift May Cause Colon Cancer." 26 August 2006. About.com. 21 June, 2012. < http://coloncancer.about.com/od/cancerresearch/a/06042003.htm>
4 "Rotating Shift Work Raises Prostate Cancer Risk." 18 September 2006. Medical News Today.21 June 2012.< http://www.medicalnewstoday.com/articles/52127.php>
5 Gardner, Amanda. "Working Night-shift s May Raise Diabetes Risk, Study Shows." 7 December 2011. Huffpost Healthy Living. 21 June 2012. < http://www.huffingtonpost.com/2011/12/07/night-shift-diabetes-work-risk_n_1134845.html>
6 Keim, Brandon. "Night-shift Makes Metabolism Go Haywire." 2 March 2009. Wired Scienc. 22 June 2012. < http://www.wired.com/wiredscience/2009/03/nightshift/>