Researchers at the University of California, San Diego (UCSD) School of Medicine have found that the levels of a pituitary hormone that increases testosterone are enhanced after exposure to bright light in the early morning. The findings suggest that light exposure might serve some of the same functions for which people take testosterone and other androgens.
One of the study's authors, Daniel Kripke, M.D. UCSD professor of psychiatry, added "the study also supports data that bright light can trigger ovulation in women, which is also controlled by luteinizing hormone (LH), the pituitary hormone we studied."
Published in the current issue of the journal Neuroscience Letters (341, 2003, 25-28), the study looked at LH excretion following bright light exposure (1,000 lux) from 5-6 a.m. each morning for five days in 11 healthy men ages 19-30. The same group of men had their LH measured again after exposure to a placebo light (less than 10 lux) from 5-6 a.m. for five days.
The researchers found that LH levels were increased 69.5 percent after bright light exposure in the early morning.
The researchers also measured levels of melatonin, a hormone whose secretion is elevated in darkness at night, and inhibited by light. Previous studies in animals had indicated that melatonin secretion might inhibit the effects of light on LH. However, the UCSD team did not find such evidence in humans.
"This finding suggests that in humans, the duration of melatonin secretion may be less important in mediating light effects on LH secretion," said Shawn Youngstedt, Ph.D., UCSD assistant project scientist and one of the paper's authors.
Previous studies by the Kripke group and others have shown that bright light exposure helps alleviate the symptoms of depression. According to the study's authors, sexual dysfunction such as loss of libido and decreased sexual activity, which are known depressive symptoms as well as side effects of newly developed antidepressants, may be helped by bright light exposure.
"The effects of bright light exposure on the LH secretion of normal volunteers should be replicated in depressed patients to elucidate the therapeutic effect of light exposure on the decreased LH levels and sexual dysfunctions of depression," the authors stated in the paper.
The paper's first author was In-Young Yoon, M.D., Ph.D., formerly a visiting scholar at UCSD and currently an assistant professor, Seoul National University School of Medicine, Korea. Jeffrey A. Elliott, Ph.D., UCSD associate research scientist was also an author on the paper. The study was supported by the National Institutes of Health.
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