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Light of our lives
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I found Janet Raloff's article "Does Light Have A Dark Side?"
(SN: 10/17/98, p. 248) quite intriguing, but I am puzzled by the researchers'
interpretation of their results. They reasoned that since eye cells in
profoundly blind people were not responsive to light, they could not signal a
decrease in nighttime melatonin production.
Recent research, however, has demonstrated that not only the eyes but cells
scattered throughout the entire body respond to light and may be responsible
for regulating the biological clock. Sighted and nonsighted populations would
not differ in this regard. Why, then, should there be any difference in two
groups' incidences of light-induced cancer?
Miriam Ruff
Silver Spring, Md.
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The work to which you refer, on skin sensors of light, is quite new and
has not been successfully replicated. Steven Lockley, one of the sources for
this article, attempted such a replication. Lockley's team irradiated the
back of the knees of blindfolded men. Yet even 67,500 lux, in 3-hour exposures
beginning at midnight, did not suppress melatonin. The researchers argue that
these new data, reported in the September Journal of Clinical
Endocrinology and Metabolism, "support the established view that
intact, uncovered eyes are a prerequisite for light-induced suppression of
melatonin in humans." —J. Raloff
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With regard to your article, I must admit to being very skittish about
applying research on nocturnal animals to diurnal ones when it comes to
exposure to light. My concern is amplified considerably when I read "5
lux. . .a little more illumination than. . .full moonlight." Full
moonlight—moon overhead on a clear night—is at best 0.1 lux. This is
one-fiftieth of 5 lux, a minimum recommended level for parking lots. Also, the
0.2 lux referred to in the sidebar is twice full moonlight and far above the
"typical moonless night." The above figures are taken from the
Illuminating Engineering Society Handbook.
Bill F. Jones
Orange, Calif.
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Connections between extended light and cancer are not entirely new. In 1956,
I reported that in female rats reared and kept lifelong under constant light,
puberty was accelerated and estrous cycles soon reverted to permanent estrus
(Endokrinologie 33: 129-138, 1956). Daily injections of a pineal
extract (melatonin was not yet available) prevented permanent estrus and kept
estral cyclicity going despite constant exposure to light (Endokrinologie
33: 287-295, 1956).
Keeping a strain of mice prone to develop mammary tumors under constant
light did not interfere with estral cyclicity but prolonged estrous periods,
accelerating occurrence of and death from mammary tumors significantly over
that of controls kept in 12 hours light12 hours darkness (Ann. N.Y. Acad.
Sci., vol. 117, 88-104, 1964).
Wolfgang Jöchle
Denville, N.J.
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Since humans are forever trying to beat the system, what about using a
light-blocking mask that covers the eyes? The article's photograph implies
that experimentation with masks is being done, but there was no mention of
results. If the eyes are truly the primary photosensors affecting the
melatonin cycle, it may be much easier to block the light at the eye rather
than trying to prevent light, from its many modern-day sources, from entering
a room.
David Hattery
Washington, D.C.
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In winter, when the nights grow long,
My mind begins to quail and cower.
The only way to stave this off
Is burn the lights at every hour.
This helps a lot to ease the pain
Of what they're lately calling SAD.
Light gets me through the winter months;
But now you tell me that it's bad!
If winter lights cause cancerous growths,
I really don't know what to do.
Should I go wacko in the dark,
Or risk a fatal tumor or two?
I'll likely light the lamps as usual
To keep myself from out the dumps.
But I'll also daily probe my flesh
For any new suspicious lumps.
Thanks for nothing, Science News.
Matt Hinton
Trinidad, Calif.
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