Circadian Disruption and Breast Cancer [chapter]

Richard G. Stevens
2001 The Pineal Gland and Cancer  
The global impact of breast cancer is large and growing. It seems clear that something about modern life is the culprit, yet there is thus far a lack of satisfactory explanations for most of the increases in risk as societies industrialize. Support has developed for a possible role of "circadian disruption," particularly from an altered-lighted environment (such as light at night). Lighting during the night of sufficient intensity can disrupt circadian rhythms, including reduction of
more » ... melatonin levels and resetting of the circadian pacemaker of the suprachiasmatic nuclei. Reduced melatonin may increase breast cancer risk through several mechanisms, including increased estrogen production and altered estrogen receptor function. The genes that drive the circadian rhythm are emerging as central players in gene regulation throughout the organism, particularly for cell-cycle regulatory genes and the genes of apoptosis. Aspects of modern life that can disrupt circadian rhythms during the key developmental periods (eg, in utero and during adolescence) may be particularly harmful. Epidemiologic studies should consider gene and environment interactions such as circadian gene variants and shift work requirements on the job. (Epidemiology 2005;16: 254 -258) B reast cancer is the leading cause of cancer death among women worldwide. Risk of breast cancer varies 5-fold among countries, is increasing everywhere, and is highest in the industrialized nations. 1 Less than half the risk in industrialized areas can be explained by changes in the known risk factors for breast cancer. 2 As societies industrialize, there are changes in many aspects of life, prominent among which is the opportunity for circadian disruption from use of artificial lighting. 3,4 Circadian rhythms are controlled by a core of 8 genes, which also exert control over key cell-cycle checkpoint genes and genes of apoptosis. 5 These rhythms can be altered by ill-timed artificial lighting and by lack of sunlight. In modern industrialized societies where people live most of their lives inside buildings, people receive very little sunlight. 6 There is also evidence that sleep patterns and melatonin production have been altered in people by the lighting practices in the modern urban environment. 7,8
doi:10.1007/978-3-642-59512-7_28 fatcat:vb6fpotvuvhezg63vtp3azfzpq