[DSLF] Digest Number 1818

[DarkSky-list@yahoogroups...]

There is 1 message in this issue.

Topics in this digest:

      1. Light at night-cancer risk in humans verified
           From: Stephen Pauley <spauley2@cox...>


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Message: 1         
   Date: Mon, 05 Dec 2005 19:24:46 -0700
   From: Stephen Pauley <spauley2@cox...>
Subject: Light at night-cancer risk in humans verified

Shigemi wrote
<<One example of such research, although its sample is small, is made by
Kochi University. It shows exposure of bright light of 2000 lux and even
moderate lights of 200- 300 lux from fluorescent light bulbs can inhibit
melatonin concentration in adolescents. The paper can be obtained at;
http://www.jcircadianrhythms.com/content/2/1/4>>
============
Thanks Shigemi.  I know of this paper.  As you know there are many studies
out there showing mlt. suppression with various illum. levels of white light.
It's hard to zero in on the lowest illum. level of white light that 
will cause this
suppression.  Perhaps the lowest for white light was reported by 
Zeiter et al.  They
found mlt. suppression with 10 fc. of white light.
http://jp.physoc.org/cgi/content/full/526/3/695

And Brainard found just .01 fc of blue light (464 nm) would suppress human mlt.

**But do those low illum. levels and subsequent lower mlt levels also 
cause cancers to grow?
How long does the exposure have to be?  What colors?
Those remain the big questions.

So what we need now are the studies that show not just the 
suppression of mlt by low illum.
levels but also find out if the resulting low levels of human mlt 
also allow cancer cells
to grow.  Dr Blask now has the experimental model to do this by infusing
human blood into rat models that have implanted human breast and 
liver cancer cells.

BTW, in rats, the illum. level of white light that will suppress mlt 
and cause cancer
cells to grow is just .02 fc - twice the light of a full moon.

While more studies are needed, I think it is wise to practice the 
Precautionary Principle.
Assume the cancer stimulating effect does occur at low levels,
place no lights or at least use fully shielded lights in residential areas, and
sleep in total darkness.

Steve Pauley




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