How Light Therapy Works in the Body

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How Light Therapy Works in the Body

Light Triggers Hormone Surge, Studies of Mice Show

By Miranda Hitti

WebMD Medical News

Reviewed By Louise Chang, MD

on Tuesday, November 08, 2005

Nov. 8, 2005 -- Bright light is known to affect the body and its

internal " clock, " and Japanese scientists may have partly figured out

how that happens.

When they exposed mice to bright light, the mice experienced a wave

of hormones called glucocorticoids. These hormones are responsible

for many bodily processes including metabolism, response to stress,

inflammation, and immunity.

Atsushi Ishida and colleagues report their findings in Cell

Metabolism. Ishida works in Kobe, Japan, in the brain science

department of Kobe University's medical school.

The study doesn't change the use of light therapy in people for

conditions including sleep disorders and some types of depression,

such as seasonal affective disorder (SAD)seasonal affective disorder

(SAD). But it might explain one aspect of how light therapy works.

From Darkness to Bright Light

Ishida's team did a series of tests on mice. In one experiment, mice

were briefly kept in constant darkness and then exposed to a short

session of bright light.

Next, the researchers checked the genes in the mice's adrenal glands.

Located atop the kidneys, the adrenal glands make glucocorticoid

hormones.

Exposure to light boosted gene activity in the mice's adrenal glands.

That upped production of hormones made by the adrenal glands. Those

hormones could then travel throughout the body, docking on virtually

any cell to rev up cell metabolism.

The intensity of the light determined the size of the hormonal

response. Very intense light prompted a bigger hormonal surge, the

study shows.

Brain Link

The process started in the mice's brains, the researchers report.

They focused on a brain area that's deeply involved in the internal

" body clock. "

That brain area is called the suprachiasmatic nucleus.

In another test, researchers took the suprachiasmatic nucleus out of

the loop. When that happened, the mice didn't show the same hormonal

reaction to bright light.

What About People?

The tests weren't done on humans. If the results apply to humans, it

could be " of great physiological interest " for doctors and

researchers, editorialists write.

They point out that it would be pretty easy to check hormone levels

after light exposure. They also note that the findings might explain

light therapy's benefits for SAD patients and those with other types

of depression that aren't usually associated with the internal clock.

The editorialists included Ueli Schibler, who works in Switzerland in

the University of Geneva's molecular biology department. Schibler and

colleagues weren't involved in Ishida's experiments.

SOURCES: Ishida, A. Cell Metabolism, November 2005; vol 2: pp

297-307. Schibler, U. Cell Metabolism, November 2005; vol 2: pp

278-281. News release, Cell Press.

http://www.webmd.com/content/Article/114/111460.htm