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Higher urinary melatonin level associated with lower risk of breast cancer
A report published in the July 20 2005 issue of the Journal of the National Cancer Institute (http://jncicancerspectrum.oxfordjournals.org/) revealed a correlation between greater levels of a metabolite of melatonin in the urine and a lowered risk of invasive breast cancer in women. The metabolite, 6-sulphatoxymelatonin, is highly correlated with blood and salivary melatonin levels.
Eva S. Schernhammer and Susan E. Hankinson of Harvard University evaluated 438 participants in the Nurses’ Health Study II, which enrolled 116,671 female nurses between the ages of 25 and 42 in 1989. The current study compared 147 women with invasive breast cancer and 291 matched controls who had agreed to participate in a substudy in which blood and urine samples were collected. First morning urine samples were used for 6-sulphatoxymelatonin measurement.
Drs Shernhammer and Hankinson found a strong inverse correlation between the risk of invasive breast cancer and urinary melatonin levels. Women whose melatonin levels were in the highest one-fourth of participants experienced a 41 percent lower risk of invasive breast cancer than those whose levels were in the lowest fourth. Those whose melatonin levels placed them in the second and third quarters also experienced a risk reduction compared to women in the lowest fourth. When women who worked at night (a factor that has been linked with an elevated risk of breast cancer) were excluded from the analysis, the risk remained basically the same.
The authors summarize their findings by stating that melatonin secretion may play an important role in breast cancer development. This study contributes to a growing body of evidence concerning the role that decreased melatonin production plays in breast cancer risk.
One of the most important supplements for a breast cancer patient is the hormone melatonin. Melatonin inhibits human breast cancer cell growth (Cos et al. 2000) and reduces tumor spread and invasiveness in vitro (Cos et al.1998). Indeed, it has been suggested that melatonin acts as a naturally occurring anti-estrogen on tumor cells, as it down-regulates hormones responsible for the growth of hormone-dependent mammary tumors (Torres-Farfan 2003).
A high percentage of women with estrogen-receptor-positive breast cancer have low plasma melatonin levels (Brzezinski et al. 1997). There have been some studies demonstrating changes in melatonin levels in breast cancer patients; specifically, women with breast cancer were found to have lower melatonin levels than women without breast cancer (Oosthuizen et al. 1989). Normally, women undergo a seasonal variation in the production of certain hormones, such as melatonin. However, it was found that women with breast cancer did not have a seasonal variation in melatonin levels, as did the healthy women (Holdaway et al. 1997).
Low levels of melatonin have been associated with breast cancer occurrence and development. Women who work predominantly at night and are exposed to light, which inhibits melatonin production and alters the circadian rhythm, have an increased risk of breast cancer development (Schernhammer et al. 2003). In contrast, higher melatonin levels have been found in blind and visually impaired people, along with correspondingly lower incidences of cancer compared to those with normal vision, thus suggesting a role for melatonin in the reduction of cancer incidence (Feychting et al. 1998).
In tumorigenesis studies, melatonin reduced the incidence and growth rate of breast tumors and slowed breast cancer development (Subramanian et al. 1991). Furthermore, prolonged oral melatonin administration significantly reduced the development of existing mammary tumors in animals (Rao et al. 2000).
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