Letters.

Light of our lives

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.

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

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.

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 light-12 hours darkness (Ann. N.Y. Acad. Sci., vol. 117, 88-104, 1964).

Wolfgang Jochle

Denville, N.J.

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.

   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.

Aid for brain deficits?

While the most recent findings on the growth of new brain cells by Fred H. Gage and Peter S. Eriksson lead to speculation about treatment for those with "strokes or who have neurodegenerative illnesses" ("Adult human brains add new cells," SN: 10/31/98, p. 276), this news may eventually also aid the palsied and the retarded/developmentally disabled.

I am led to wonder whether we may now look for a new mechanism with which to aid individuals with brain damage caused at or before birth, whether by trauma or disease or genetics. Could deficit cell areas of the brain be "repaired" or "added to" using this new combined knowledge?

Certainly, the need in the brain-damaged/ deficit population is as significant as in the stroke and trauma population, and, perhaps, a true treatment may be near for both.

Irwin Tyler

Spring Valley, N. Y.

Fair warning

In "Is natural pesticide too hard on people?" (SN: 11/7/98, p. 295), B. cepacia is proposed for use as natural biological protection for seeds and fruits. Concerns are raised because B. cepacia is a potent pathogen in patients with cystic fibrosis. B. cepacia is also a major cause of pneumonias in patients with chronic granulomatous disease. If levels of B. cepacia on seed, fruits, or cuttings are significantly increased over natural levels by design, then susceptible individuals who come in contact with these products will be at significantly greater risk of infection. Companies contemplating the widespread environmental use of such agents should not discount their liability to provide warnings to protect at-risk individuals.

Harry Malech

National Institutes of Health

Bethesda, Md.