How Light Therapy Works in the Body
Light Triggers Hormone Surge, Studies of Mice Show
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
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
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 . 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
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
The intensity of the light determined the size of the hormonal response.
Very intense light prompted a bigger hormonal surge, the study shows.
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
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
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,
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.