Night Work and Cancer Risk
By Joan Edstrom
There have been significant research results indicating an association between light exposure during the evening and breast and colon cancer. A study of women at the Danish Institute of Cancer Epidemiology reported that women who had worked in careers such as flight attending, catering, and worked more than 60% at night for a minimum of six months had a 50 per cent greater incidence of breast cancer.
Another study by Harvard Medical School of 80,000 nurses shows that women who swing regularly from day to night work raise their risk of colon and rectal cancer by 35%. (Research studies are not 100% conclusive and it should be noted that research is ongoing.)
Here is the theory behind the link between night work and cancer risk: Light is the primary stimulus to the disruption and resetting of our pineal gland located in the hypothalamus area of the brain. The pineal gland controls our melatonin production and is turned on at night, and is turned off by detectable light. Melatonin is a hormone that protects us from the growth of tumors by increasing our immune response, by reducing estrogen, which promotes cell growth in the breast, and by grabbing up free radicals (caused by the fat we eat- tumors love fatty acids).
Our production of melatonin follows our circadian (day/night internal) clock. Our pineal gland starts making melatonin around eight o’clock p.m., but only in the dark. The amount produced peaks around 3 a.m. and ebbs by 7 a.m. Any light during the night such as moonlight, night lights, clock light, or bathroom lights will shut down the gland. When we go back to darkness, the gland will resume production, but the amount of melatonin will not reach peak levels again for the night.
There are ways for night shift workers to reduce cancer risk. Working consistently just at night will eventually enable a person to produce melatonin during the day while sleeping. Also, risk can be reduced by eating a vegetable-rich diet low in saturated fat, exercising and by refraining from smoking.
Hansen, Johnni. "Increased breast cancer risk among women who work predominantly at night." Epidemiology 12 (2001): 74-77. Jan. 2001
Schernhammer, Eva. “Melatonin and cancer risk, Does light at night compromise physiologic cancer protection by lowering serum melatonin levels?.” British Journal of Cancer 90 (2004): 941-943.
Dawidowska, Kasia. Prevention. Emmaus: Nov 2003. Vol 55, Iss. 11; pg 178
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