> Interference With Production of Key Hormone
>
> http://www.washingtonpost.com/wp-dyn/content/article/2008/02/19/AR2008021902398.html?sub=new By Rick Weiss Washington Post Staff Writer
> Wednesday, February 20, 2008
>
> Women who live in neighborhoods with large amounts of nighttime illumination
> are more likely to get breast cancer than those who live in areas where
> nocturnal darkness prevails, according to an unusual study that overlaid
> satellite images of Earth onto cancer registries.
>
> The finding adds credence to the hypothesis that exposure to too much light
> at night can raise the risk of breast cancer by interfering with the brain's
> production of a tumor-suppressing hormone.
>
> "By no means are we saying that light at night is the only or the major risk
> factor for breast cancer," said Itai Kloog, of the University of Haifa in
> Israel, who led the new work. "But we found a clear and strong correlation that
> should be taken into consideration."
>
> Scientists have known for years that rats raised in cages where lights are
> left on for much of the night have higher cancer rates than those allowed to
> sleep in darkness. And epidemiological studies of nurses, flight attendants
> and others who work at night have found breast cancer rates 60 percent above
> normal, even when other factors such as differences in diet are accounted for.
>
> On the basis of such studies, an arm of the World Health Organization
> announced in December its decision to classify shift work as a "probable carcino
> gen." That put the night shift in the same health-risk category as exposure to
> such toxic chemicals as trichloroethylene, vinyl chloride and polychlorinated
> biphenyls (PCBs).
>
> The mechanism of such a link, if real, remains mysterious, but many
> scientists suspect that melatonin is key. Secreted by the pineal gland in the brain,
> the hormone helps prevent tumor formation. The body produces melatonin
> primarily at night, and levels drop precipitously in the presence of light,
> especially light in the blue part of the spectrum produced in quantity by computer
> screens and fluorescent bulbs.
>
> In keeping with the melatonin hypothesis, mice in cages with night lighting
> have normal cancer rates if they get shots of the hormone. And blind women,
> whose eyes cannot detect light and so have robust production of melatonin,
> have lower-than-average breast cancer rates.
>
> Kloog and his colleagues took a previously untried approach to testing the
> link. They obtained satellite data from NASA that showed in great detail how
> much light was emitted spaceward from neighborhoods throughout Israel.
>
> Although the light levels that reached the satellite were about one-tenth
> their intensity on Earth, the approach provides an accurate measure of which
> areas are brighter or darker than others and by how much.
>
> The team then overlaid that map with local statistics on cases of breast
> cancer and, for comparison, lung cancer, which is caused mostly by smoking and
> so would not be expected to be linked to light.
>
> After using neighborhood data to correct for other factors that can affect
> cancer rates, including wealth, ethnicity and the average number of children
> in families living in those localities, the researchers found no link between
> night lighting and lung cancer, they report in this week's online issue of
> the journal Chronobiology International.
>
> But the researchers found the breast cancer rate in localities with average
> night lighting to be 37 percent higher than in communities with the lowest
> amount of light; and they noted that the rate was higher by an additional 27
> percent in areas with the highest amount of light.
>
> Abraham Haim, a University of Haifa chronobiologist involved in the study,
> said the findings raise questions about the recent push to switch to
> energy-efficient fluorescent bulbs, which suppress melatonin production more than
> conventional incandescent bulbs. "This may be a disaster in another 20 years,"
> Haim said, "and you won't be able to reverse what we did by mistake." He called
> for more research before policies favoring fluorescent lights are
> implemented, and for more emphasis on using less light at night.
>
> Jim Burch, a University of South Carolina epidemiologist and biostatistician
> familiar with the study, called the approach and findings "fascinating."
>
> "The study has limitations," including not measuring levels of indoor
> lighting, "but it supports the overall idea," Burch said. "I think there is enough
> evidence to suggest we ought to be thinking about this more carefully."
>
> For more news, or to subscribe to the newspaper, please visit
> http://www.washingtonpost.com
>
**************
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[Non-text portions of this message have been removed]
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