Melatonin and cancer risk: does light at night compromise physiologic cancer protection by lowering serum melatonin levels?

Abstract

The suprachiasmatic nuclei in the hypothalamus, one of the most important physiological determinants of alertness and performance, drive a circadian pacemaker in mammals, with an intrinsic period averaging 24 h. Light is the primary stimulus to the disruption and resetting of this pacemaker, which is expressed in changing melatonin rhythms. Melatonin production in humans decreases when people are exposed to light at night. Since melatonin shows potential oncostatic action in a variety of tumours, it is possible that lowered serum melatonin levels caused by exposure to light at night enhance the general tumour development. Cancer is the second leading cause of death in industrialised countries like the United States, where a significant proportion of workers engage in shift work, making a hypothesised relation between light exposure at night and cancer risk relevant. Observational studies support an association between night work and cancer risk. We hypothesise that the potential primary culprit for this observed association is the lack of melatonin, a cancer-protective agent whose production is severely diminished in people exposed to light at night.

The frequencies of micronuclei induced by cisplatin in newborn rat astrocytes are increased by 50-Hz, 7.5- and 10-mT electromagnetic fields

“…Many reports have demonstrated that melatonin inhibits the growth of a wide range of cancers (30). Melatonin's oncostatic effects involve complex interactions with hormones, growth factors, cytokines, and their receptors as well as various signaltransduction pathways, cytoskeletal elements, and oncogenes (30). A reduction in melatonin may 1) increase proliferation of stem cells at risk, 2) stimulate proliferation of cancer cells, and 3) impair immune function (31,32).…”

Sleep duration and the risk of prostate cancer: the Ohsaki Cohort Study

“…Melatonin may be a factor in these inverse associations with sex hormone-related cancers (Brzezinski, 1997;Schernhammer and Schulmeister, 2004;Shiu, 2007). A decreased sleep duration results in a shorter duration of nocturnal melatonin secretion (Wehr, 1991).…”

“…Pinheiro et al, 2006). Melatonin, which is secreted mainly from the pineal gland and plays a role in sleep duration, is suggested as one of the candidates responsible for the association in breast cancer (Brzezinski, 1997;Schernhammer and Schulmeister, 2004) as it influences the synthesis and secretion of sex hormones by promoting the release of gonadotropin-releasing hormone (Martin and Klein, 1976;Aleandri et al, 1996).…”

“…Pinheiro et al, 2006). Melatonin, which is secreted mainly from the pineal gland and plays a role in sleep duration, is suggested as one of the candidates responsible for the association in breast cancer (Brzezinski, 1997;Schernhammer and Schulmeister, 2004) as it influences the synthesis and secretion of sex hormones by promoting the release of gonadotropin-releasing hormone (Martin and Klein, 1976;Aleandri et al, 1996).In relation to melatonin, there have been several observational studies of night work, shift work or visual impairment, and sex hormone-related cancers such as prostate or breast (Feychting et al, 1998;Verkasalo et al, 1999;Kliukiene et al, 2001;Megdal et al, 2005;Kubo et al, 2006;Conlon et al, 2007;Schwartzbaum et al, 2007). However, there has been no study of sleep duration and prostate cancer risk, even though prostate cancer, like breast cancer, is also a sex hormone-related cancer.…”

Circadian Oscillations of Clock Genes, Cytolytic Factors, and Cytokines in Rat NK Cells

“…Circadian rhythms seem to be particularly relevant in cardiovascular diseases (68), immune responses (69), and cancer (70,71). It has been shown in mice that chronic jet lag disrupts circadian gene expression and accelerates tumor growth (72).…”