Artificial Light At Night Stimulates Breast Cancer Growth In Laboratory

Date: 2005-12-20


http://www.niehs.nih.gov/oc/news/cancerlight.htm


Artificial Light At Night Stimulates Breast Cancer Growth In Laboratory

Mice


Results from a new study in laboratory mice show that nighttime
exposure to artificial light stimulated the growth of human breast
tumors by suppressing the levels of a key hormone called melatonin. The

study also showed that extended periods of nighttime darkness greatly
slowed the growth of these tumors.


The study results might explain why female night shift workers have a
higher rate of breast cancer. It also offers a promising new
explanation for the epidemic rise in breast cancer incidence in
industrialized countries like the United States.


The National Cancer Institute and the National Institute of
Environmental Health Sciences, agencies of the federal National
Institutes of Health, provided funding to researchers at the Bassett
Research Institute of the Mary Imogene Bassett Hospital in Cooperstown,

New York and The Thomas Jefferson University in Philadelphia, Pa. The
results are published in the December 1, 2005 issue of the scientific
journal Cancer Research.


"This is the first experimental evidence that artificial light plays an

integral role in the growth of human breast cancer," said NIEHS
Director David A. Schwartz, M.D. "This finding will enable scientists
to develop new strategies for evaluating the effects of light and other

environmental factors on cancer growth."


"The risk of developing breast cancer is about five times higher in
industrialized nations than it is in underdeveloped countries," said
Les Reinlib, Ph.D., a program administrator with the NIEHS' grants
division. "These results suggest that the increasing nighttime use of
electric lighting, both at home and in the workplace, may be a
significant factor."


Previous research showed that artificial light suppresses the brain's
production of melatonin, a hormone that helps to regulate a person's
sleeping and waking cycles. The new study shows that melatonin also
plays a key role in the development of cancerous tumors.


"We know that many tumors are largely dependent on a nutrient called
linoleic acid, an essential fatty acid, in order to grow," said David
Blask, M.D., Ph.D., a neuroendocrinologist with the Bassett Research
Institute and lead author on the study. "Melatonin interferes with the
tumor's ability to use linoleic acid as a growth signal, which causes
tumor metabolism and growth activity to shut down."


To test this hypothesis, the researchers injected human breast cancer
cells into laboratory mice. Once these cells developed into cancerous
tumors, the tumors were implanted into female rats where they could
continue to grow and develop.


The researchers then took blood samples from 12 healthy, premenopausal
volunteers. The samples were collected under three different conditions

-- during the daytime, during the nighttime following 2 hours of
complete darkness, and during the nighttime following 90 minutes of
exposure to bright fluorescent light. These blood samples were then
pumped directly through the developing tumors.


"The melatonin-rich blood collected from subjects while in total
darkness severely slowed the growth of the tumors. "These results are
due to a direct effect of the melatonin on the cancer cells," said
Blask. "The melatonin is clearly suppressing tumor development and
growth."


In contrast, tests with the melatonin-depleted blood from light-exposed

subjects stimulated tumor growth. "We observed rapid growth comparable
to that seen with administration of daytime blood samples, when tumor
activity is particularly high," Blask said.


According to the researchers, melatonin exerts a strong influence on
the body's circadian rhythm, an internal biological clock that
regulates sleep-wake cycle, body temperature, endocrine functions, and
a number of disease processes including heart attack, stroke and
asthma. "Evidence is emerging that disruption of one's circadian clock
is associated with cancer in humans, and that interference with
internal timekeeping can tip the balance in favor of tumor
development," said Blask.


"The effects we are seeing are of greatest concern to people who
routinely stay in a lighted environment during times when they would
prefer to be sleeping," said Mark Rollag, Ph.D., a visiting research
scientist at the University of Virginia and one of the study
co-authors. "This is because melatonin concentrations are not elevated
during a person's normal waking hours."


"If the link between light exposure and cancer risk can be confirmed,
it could have an immediate impact on the production and use of
artificial lighting in this country," said Blask. "This might include
lighting with a wavelength and intensity that does not disrupt
melatonin levels and internal timekeeping."


"Day workers who spend their time indoors would benefit from lighting
that better mimics sunlight," added Blask. "Companies that employ shift

workers could introduce lighting that allows the workers to see without

disrupting their circadian and melatonin rhythms."


###


NIEHS, a component of the National Institutes of Health, supports
research to understand the effects of the environment on human health.
For more information on breast cancer and other environmental health
topics, visit our website at http:/​/​www.niehs.nih.gov/​.

"Tim Campbell" wrote in message
oups.com...
Date: 2005-12-20
http://www.niehs.nih.gov/oc/news/cancerlight.htm
Artificial Light At Night Stimulates Breast Cancer Growth In Laboratory
Mice
Results from a new study in laboratory mice show that nighttime
exposure to artificial light stimulated the growth of human breast
tumors by suppressing the levels of a key hormone called melatonin. The
study also showed that extended periods of nighttime darkness greatly
slowed the growth of these tumors.

That's kind of scary.
Marie

Artificial Light At Night Stimulates Breast Cancer Growth In Laboratory
Mice

Maybe this will stimulate sales of sleeping masks a little...
I've suspected for some time that the regular use of these devices to
artificially induce complete darkness would lower cancer risk, and
thereby increase human longevity by a few years.

The study results might explain why female night shift workers have a
higher rate of breast cancer. It also offers a promising new
explanation for the epidemic rise in breast cancer incidence in
industrialized countries like the United States.

That sounds like a huge stretch unless the authors either controlled
for a slew of likely confounders or cited other studies that did so.
Night shift workers likely differ from other women in a slew of ways
(diet, access to medical care, smoking patterns, occupational
exposures, etc.) and certainly industrial countries have changed in
ways involving many more potential risk factors for breast cancer than
just exposure to artificial light at night. Prior to reading this
press release, if asked for major changes in their countries in the
last 50 years (or any similar time period), how many people would have
even mentioned increased exposure to artificial light at night? Hardly
anyone, I would guess.

Jonathan Levy wrote:


That sounds like a huge stretch unless the authors either controlled
for a slew of likely confounders or cited other studies that did so.
Night shift workers likely differ from other women in a slew of ways
(diet, access to medical care, smoking patterns, occupational
exposures, etc.) and certainly industrial countries have changed in
ways involving many more potential risk factors for breast cancer than
just exposure to artificial light at night. Prior to reading this
press release, if asked for major changes in their countries in the
last 50 years (or any similar time period), how many people would have
even mentioned increased exposure to artificial light at night? Hardly
anyone, I would guess.

I'm not suggesting the study is valid, but it is true that one of the
huge differences between say 100 years ago and now is lighting.
A second would, I think, be the increased speed of transport.
A third would be water on tap.

I can't think of anything that's made such a difference in life-styles
as these three things.

I also read a study some time ago on chicks that suggested that chicks
raised without complete darkness at night tended to have higher rates
of myopia because the eyeball apparently grows. (Of course, I also read
that children who read a lot tend toward myopia...)

I don't think the chick study was verfied in any other animals, but am
not sure.

Jonathan Levy wrote:
The study results might explain why female night shift workers have a
higher rate of breast cancer. It also offers a promising new
explanation for the epidemic rise in breast cancer incidence in
industrialized countries like the United States.

That sounds like a huge stretch unless the authors either controlled
for a slew of likely confounders or cited other studies that did so.
Night shift workers likely differ from other women in a slew of ways
(diet, access to medical care, smoking patterns, occupational
exposures, etc.) and certainly industrial countries have changed in
ways involving many more potential risk factors for breast cancer than
just exposure to artificial light at night. Prior to reading this
press release, if asked for major changes in their countries in the
last 50 years (or any similar time period), how many people would have
even mentioned increased exposure to artificial light at night? Hardly
anyone, I would guess.

I remember reading something in Science News (and now I'll search for
it) comparing the breast cancer rates among female nurses, and that the
study saw a difference in incidence based on shift (night/day/evening).
I'll look now.

Caledonia

Caledonia wrote:
Jonathan Levy wrote:
The study results might explain why female night shift workers have a
higher rate of breast cancer. It also offers a promising new
explanation for the epidemic rise in breast cancer incidence in
industrialized countries like the United States.

That sounds like a huge stretch unless the authors either controlled
for a slew of likely confounders or cited other studies that did so.
Night shift workers likely differ from other women in a slew of ways
(diet, access to medical care, smoking patterns, occupational
exposures, etc.) and certainly industrial countries have changed in
ways involving many more potential risk factors for breast cancer than
just exposure to artificial light at night. Prior to reading this
press release, if asked for major changes in their countries in the
last 50 years (or any similar time period), how many people would have
even mentioned increased exposure to artificial light at night? Hardly
anyone, I would guess.

I remember reading something in Science News (and now I'll search for
it) comparing the breast cancer rates among female nurses, and that the
study saw a difference in incidence based on shift (night/day/evening).
I'll look now.

Following up my own post (Science News content is subscriber only,
alas) -- the breast cancer melatonin studies were initially reported in
the October 17 2001 Journal of the National Cancer Insitute; follow-on
studies from June 4, 2003 (same journal) also indicate a hightened risk
of colorectoral cancer.

The link between melatonin and faster tumor growth in rodents is from
the late 90's I believe...

Caledonia

I have read this study and it brought to mind that when I was a
youngster the lady next door had grow lights that would shine into my
bedroom at night over the african violets she sold.

I have wondered if this is the reason my eyesight was so poor that I
had to begin wearing glasses at age 9 while nobody else in my family
has had to wear glasses before requiring reading glasses in their 50s
and 60s.

Something to think about.

mypet wrote:

I have read this study and it brought to mind that when I was a
youngster the lady next door had grow lights that would shine into my
bedroom at night over the african violets she sold.

I have wondered if this is the reason my eyesight was so poor that I
had to begin wearing glasses at age 9 while nobody else in my family
has had to wear glasses before requiring reading glasses in their 50s
and 60s.

Something to think about.
---------------------
No.
Glasses are prescribed/used for many different reasons. Yours were
NOT for presbyopia, the aging of the accomodative capacity of the
lenses and resultant slight far-sightedness for reading purposes.

Yours were likely for near-sightedness and none such are caused by
distant lights. And Gro-Lights are not dangerous, merely a slightly
more sun-like spectrum. The sun would be a more likely cause, but
that's quite doubtful as well.
Steve