Ultra-bright lamps may boost the body's ability to produce sex hormones, particularly for men, say researchers who studied the effects of light therapy on mood.

The importance of the finding is not fully established, but it's possible that light therapy could one day be used to control ovulation in women or treat people who take antidepressants and find themselves with low sex drives, the researchers say.

"It's a very promising lead," says study co-author Dr. Daniel Kripke, a professor of psychiatry emeritus at the University of California at San Diego.

Researchers have known for decades that exposure to light affects the way animals live. Changes in the light from the sun, for example, set off hibernation in some mammals. Seasonal changes in light also control reproduction in rats and mice; they only mate during warmer months, Kripke says.


Researchers are still working to understand how exposure to light affects humans. Kripke and colleagues discovered two decades ago that light therapy—shining powerful lamps at people's eyes—affects mood. Light therapy has become a common treatment for seasonal affective disorder, a type of depression that strikes when days grow shorter.

In his study, Kripke enlisted 11 healthy men, aged 19 to 30 years, to test whether light affects the body levels of luteinizing hormone, which is produced by the pituitary gland and also leads to the release of other hormones, such as testosterone in men. The men woke at 5 am for five days and spent an hour in front of a light box giving off 1,000 lux, much more brightness than typical indoor lighting. Later, they spent five days in front of a light box that only gave out 10 lux.

The result: Body levels of luteinizing hormone grew by nearly 70% while the men were exposed to the higher levels of light.

The researchers didn't look at women because the rapidly cycling hormones in their bodies would make it difficult to study the effect, Kripke says. However luteinizing hormone does affect ovulation, he adds, and "we think light is potentially a very promising treatment for women who have ovulatory problems or long and irregular menstrual cycles."


Light therapy could also boost testosterone in men, potentially increasing sexual potency and muscle mass, he says. Researchers, however, did not monitor testosterone levels in the men.

A hormone expert cautioned that research is still needed. The study was small, and it's not clear whether the changes in the level of the hormone are significant enough to actually cause changes in the body, says Dr. Ronald Swerdloff, chief of the division of endocrinology at Harbor UCLA Medical Center, part of the University of California at Los Angeles School of Medicine.

For more information, visit the Society for Light Treatment and Biological Rhythms at www.websciences.org/sltbr.

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