© 2002 by Oxford University Press
Journal of the National Cancer Institute, Vol. 94, No. 7, 531-532,
April 3, 2002
© 2002 Oxford University Press
CORRESPONDENCE |
Re: Night Shift Work, Light at Night, and Risk of Breast Cancer
Correspondence to: Norbert Kerenyi, M.D., FRCP(C), FRC Path., Dept. of Laboratory Medicine and Pathobiology, St. Michael's Hospital, 30 Bond St., Toronto, Ontario M5B 1W8 Canada.
A very thoughtful and thorough editorial (1) and two most interesting and valuable publications (2,3) focus attention on the role of light and melatonin production and the risk of breast cancer.
In 1990, our group put forward a comprehensive hypothesis that one of the most important etiologic factors in the increasing rate of cancers is the change in light exposure that has taken place during the last 100 years (4). The introduction of electric light generally increased the average daily light exposure by 4–6 hours. The increase in light exposure decreases the amount of time that is available for melatonin production, which reduces the nonspecific oncostatic effect of the pineal gland. This adverse effect of light exposure, according to our hypothesis, may increase the risk of other cancers. Beral et al. (5) reported that the exposure to fluorescent light in the workplace was associated with a twofold increase in the risk of melanoma compared with a matched control group. The risk increased with increasing duration of exposure to fluorescent light, with a relative excess of lesions on the trunk (5). By contrast, blind women who are not ocularly receptive to light are not influenced by the extended light exposure and have a reduced risk of breast cancer (6). Women with a milder degree of visual impairment did not have a similar reduced risk (6).
Our group surveyed workers who, every day, worked for 6–7 hours in darkness, producing films at the Canadian Kodak factory. We found that the film production workers had a reduced risk of breast cancer and of malignant melanoma compared with workers in administration or other manufacturing areas (Kerenyi N: unpublished findings).
The conclusion of the editorial by Dr. J. Hansen (1) emphasizes that there is an urgent need for further exploration regarding the effects of light exposure on cancers. I strongly agree with this conclusion. In 1973, el-Domeiri and Das Gupta (7) found that the accelerated growth of transplanted melanoma in pinealectomized hamsters could be reversed by the addition of exogenous melatonin. Considering all these facts, raising the question of whether melatonin replacement could be beneficial for the light-exposed night shift workers is justifiable. A controlled clinical study may answer this question.
REFERENCES
1
Hansen J. Light at night, shiftwork, and breast cancer risk. J Natl Cancer Inst 2001;93:1513–5.
2
Davis S, Mirick DK, Stevens RG. Night shift work, light at night, and risk of breast cancer. J Natl Cancer Inst 2001;93:1557–62.
3
Schernhammer ES, Laden F, Speizer FE, Willett WC, Hunter DJ, Kawachi I, et al. Rotating night shifts and risk of breast cancer in women participating in the nurses' health study. J Natl Cancer Inst 2001;93:1563–8.
4 Kerenyi NA, Pandula E, Feuer G. Why the incidence of cancer is increasing: the role of `light pollution'. Med Hypotheses 1990;33:75–8.[CrossRef][Web of Science][Medline]
5 Beral V, Evans S, Shaw H, Milton G. Malignant melanoma and exposure to fluorescent lighting at work. Lancet 1982;2:290–3.[Medline]
6 Kliukiene J, Tynes T, Andersen A. The risk of breast cancer among Norwegian women with visual impairment. Br J Cancer 2001;84:397–9.[CrossRef][Web of Science][Medline]
7
el-Domeiri AA, Das Gupta TK. Reversal by melatonin of the effect of pinealectomy on tumor growth. Cancer Res 1973;33: 2830–3.
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