Could electric light pose a cancer threat?

It might seem like the wildest of paranoid beliefs, but a growing number of scientists suspect it might be true. The reason: Turning on the lights after dark may affect a small number of "clock genes" that play a major role in controlling how cells live, die and function, these researchers suggest.

Specifically, the experts say, there is evidence that night lighting can help cause cancer by interfering with the molecular mechanisms that control cell death and multiplication.

A number of these researchers are in London this week for a five-day meeting where they are considering the evidence for a link between lighting at night and an increase in the incidence of childhood leukemia. The meeting, which concludes Friday, is sponsored by Children With Leukaemia, Great Britain's leading charity devoted to conquest of the disease.

There has been a steady increase in childhood leukemia rates in Britain and Europe, according to a report delivered at the meeting by Michael P. Coleman and Anjal Shah, epidemiologists at the London School of Hygiene and Tropical Medicine.

In the United States, a study by epidemiologists at the University of Minnesota found a similar increase of about 1 percent every two years between 1973 and 1998 -- but only for childhood leukemia. The incidence of adult leukemia declined during those years.

And leukemia may not be the only cancer affected by artificial lighting at night, said Richard G. Stevens, an associate professor of medicine at the University of Connecticut Health Center, who has been studying the role of clock gene malfunction in breast cancer. The results of his research are only preliminary, he noted, because the field is so young.

"The clock gene revolution is new," Stevens said. "They were only identified about five years ago. There are eight or nine of them in mammals, and they control a lot of other genes."

Some of those genes control apoptosis, the process by which the body destroys abnormal cells, among other functions. Other genes control cell division. Malfunctions of those genes can lead to cancer, as cells no longer pay attention to signals telling them not to divide or abnormal cells fail to commit suicide, Stevens said.

A possible link between electric light and cancer could be the hormone melatonin, which protects genetic material from mutation, according to Russell Reiter, professor of cellular and structural biology at the University of Texas. Night light suppresses the body's production of melatonin and thus can increase the risk of cancer-related mutations, he told the London meeting.

Scott Davis, chairman of the department of epidemiology at the University of Washington, said that while the link between light at night and cancer "may seem like a stretch on the surface, there is an underlying biological basis for it."

Davis, like Stevens, has been studying how night lighting affects the production of female hormones, which, in turn, can affect the risk of breast cancer.

"We have found a relationship between light at night and night-shift work to breast cancer risk," Davis said. "The studies indicate that night work disrupts the activity of melatonin, which leads to excessive production of hormones in women."

If the link between night light and cancer is eventually proved to be true, Stevens said, it's hard to say what could be done about it.

"So far, no therapeutic agent has been developed for it," he said.

More information

The National Sleep Foundation has more about melatonin.

Reference Source 101
September 10, 2004

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