A long-term study featured in the journal Occupational and Environmental Medicine reveals that working more than two night shifts per week poses agreater risk of breast cancer. The risk appears cumulatively higher in those who describethemselves as 'early birds' or 'morning people' than 'owls' or'night birds'. After discovering that shift work disrupts the body's clock(circadian rythms) and is "probably carcinogenic", theInternational Agency for Research on Cancer (IARC) called for moreresearch in 2007. One in 10 people in Europe and one in five peoplein the US are night workers. |
Earlier studies in nurses who might beexposed to other cancer causing agents have excluded other potential influential factorslike sunlight exposure for instance. The researchers managed to recruit 210 of the 218 women agedbetween 44 and 83 years old who worked for the Danish Army between1964 and 1999 and who suffered from breast cancer between 1990 and 2003 and who were still alive in 2005 and 2006. The women were matched with 899 women of the same age who alsoworked for the Danish Army but who did not have breast cancer. 141women with breast cancer and 551 without the disease were asked tocomplete a comprehensive 28-page questionnaire, which includedquestions related to their jobs and working patters, in addition tolifestyle questions with regard to their reproductive history, useof contraceptives, hormone replacement therapy , and sun bathing habits. The participants were also asked if theywere a "morning" or "evening" person, or neither (diurnalpatterns).
The outcome based on 693 responses demonstrated that overall thosewho worked night shifts had a 40% higher risk of breast cancer thanthose who did not work night shifts. The risk was even higher, i.e.50% in women who worked a minimum of three night shifts a week fora minimum of six years. The researchers found that those who worked these shift patternsfor this amount of time had an even greater likelihood if they were'morning' persons. Their risk was almost four times higher opposedto those not working night shifts.
The researchers believe that oneof the reasons could be that morning types are more susceptible tobody clock disruption. Whilst "Owls" were twice as likely todevelop breast cancer, the overall risk was even lower for 'earlybirds' who did not work night shifts. The researchers state thatalthough insufficient sunlight has been associated with thedevelopment of various cancers, they found that those who workednight shifts tended to sunbathe more often than those workingduring the day. The researchers concluded that up to two night shifts per week didnot influence the risk of developing breast cancer, as it may benot be long enough to disrupt the body clock, whereas frequentnight shifts over a period of several years may disrupt the bodyclock and normal sleep patterns, in addition to compromising theproduction of melatonin, a cancer protecting hormone, which may beassociated with developing or progression of breast cancer cells. Written By Petra Rattue Copyright: Medical News Today Not to be reproduced without permission of Medical News Today Additional References Citations.
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