[ RadSafe ] " Link found between light, breast cancer "

[Jaro]

http://www.theglobeandmail.com/servlet/ArticleNews/TPStory/LAC/20060114/CANC
ER14/Health/Idx
Link found between light, breast cancer
Nighttime exposure to electric lighting curbs production of vital melatonin,
researchers find
Saturday, January 14, 2006 Page A15
By MARTIN MITTELSTAEDT, ENVIRONMENT REPORTER

 The high rate of breast cancer in industrialized countries has long puzzled
medical researchers, but a team of U.S. scientists has discovered a possible
explanation for why women in developed countries are at high risk of
developing the disease.

The answer at first glance may seem unlikely: nighttime exposure to electric
lighting.

In a major breakthrough, researchers have linked exposure to light at night
to the growth in breast-cancer tumours. The tumours grew because artificial
light interfered with the ability of women to create melatonin, the hormone
that regulates the body's daytime and night rhythms.

The discovery holds major public-health implications because most women in
industrial societies turn on lights at night in their homes and offices and
may potentially be at risk from this exposure.

 "Light, in terms of our experiments, stimulates breast-cancer growth
activity, and obviously this is due to the ability of light to shut off
melatonin production," said David Blask, a scientist with the Bassett
Research Institute in Cooperstown, N.Y., who led the team that made the
discovery.

He said, "melatonin puts cancer cells, in particular breast-cancer cells, to
sleep at night," but if the levels of this hormone are diminished by
exposure to light at night, cancers "become insomniacs" and grow all the
time.

In recent years, there has been a flurry of research suggesting light at
night may be a health hazard, causing illnesses ranging from chronic fatigue
to depression.

But until now, there has only been circumstantial evidence linking it to
breast cancer. For instance, women who regularly work overnight "graveyard"
shifts have been found to have an elevated incidence of the disease, in some
cases up to 60 per cent higher than those who work regular day shifts.

This new research, outlined last month in the journal Cancer Research, is
the first experimental evidence to show that light at night can have an
effect similar to a cancer-promoting chemical.

"Electric lighting as a driver of the breast-cancer epidemic worldwide --
that's a dramatic big thing, and new," said Richard Stevens, an
epidemiologist at the University of Connecticut who has studied the health
risks of light pollution.

The U.S. National Institutes of Health, which financed the study, hailed the
results and said they offer "a promising new explanation for the epidemic
rise in breast-cancer incidence in industrialized countries like the United
States."

Les Reinlib, a program administrator for the agency, said the discovery may
hold promising avenues for preventing breast cancer with simple steps, such
as changing women's exposure to light at night. He also said that melatonin,
an inexpensive and widely available hormone supplement, should be studied to
see whether it holds promise as an anti-cancer therapy.

Breast cancer is the most frequently diagnosed cancer among Canadian women,
with about 21,600 new cases diagnosed annually. About 5,300 women die each
year of the disease.

Dr. Stevens said the high breast-cancer incidence in industrialized
countries, at about five times that of poor countries, has long intrigued
researchers. "We have what I would call an epidemic of breast cancer and we
don't know why," he said.

Studies into possible explanations, such as the high-fat Western diet,
pesticides, or industrial pollutants, have generally been inconclusive,
suggesting that there is something else that is ubiquitous in affluent
countries that is causing the disease.

Breast cancer is linked to genetics, early menstruation, and reproductive
history, among other things, but about 60 per cent of those with the disease
have no currently known risk factor.

The researchers found that melatonin plays a key role in inhibiting the
growth of breast-cancer tumours. Melatonin is produced in the brain's pineal
gland, guided by cues from the retinas in the eyes, and circulates in the
blood. The hormone is produced only when it is dark, beginning at nightfall,
with production peaking in the middle of the night, and then shutting off
during the day. When people are exposed to light at night, the body thinks
it is daytime and melatonin formation stops.

To track melatonin's impact, Dr. Blask's team implanted human breast-cancer
tumours in rats, then isolated the tumours so they were fed blood from a
single artery and drained by only one vein. They then pumped blood from
premenopausal female volunteers through the cancer cells.

Melatonin-rich blood drawn from women who were in darkness markedly
suppressed the growth of the tumours. But when the women were exposed to
fluorescent light at night, causing their melatonin levels to drop, tumour
growth took off. Tumour growth also increased when the breast-cancer cells
were exposed to melatonin-deficient blood collected during daytime.

The melatonin-rich blood was drawn from women at 2 a.m., after two hours of
complete darkness in an office room. They were exposed to 90 minutes of
bright, fluorescent office-style lighting, after which another blood sample,
this one with low melatonin, was taken. The daytime blood sample was taken
from 10 a.m. to 2 p.m., a period when melatonin levels normally fall because
of exposure to sunlight.

The experiment represented as close to a human test as possible without
actually using women as test subjects, something that would be impractical
and unethical. But because the tests were conducted using human blood and
human cancer cells, the scientists feel certain the experiment indicates
what is happening in women.

Although the research is considered a breakthrough, it has limitations. For
one thing, it didn't indicate what levels of lighting are safe. The bulb
used in the experiment was an ordinary fluorescent office light, but the
brightness of the light was high -- about the amount used at a drafting
table.

Researchers have found that almost all electric lighting has some
melatonin-dampening effect, but they have yet to work out a dose-response
relationship for cancer cells.

Nor did the study address what initially causes women to develop cancer
cells. Scientists believe almost everyone generates some cancer cells during
their lives, but the immune system manages to contain the aberrant cells
before they develop into dangerous tumours.

 In a separate test, the U.S. researchers found that melatonin blocks the
growth of liver tumours in rats, suggesting a far wider impact than on
breast cancer alone. Many researchers suspect that the incidence of prostate
cancer, a disease in men in industrialized countries that has had the same
explosive growth as breast cancer among women, might also be linked to light
pollution.

Dr. Blask said melatonin has a beneficial effect because it literally
starves the cancer of material needed to grow. It blocks the absorption into
cancer cells of a compound contained in polyunsaturated dietary fat, from
foods such as corn oil, that spurs tumour growth.

He speculated that light at night causes a melatonin deficiency, allowing
breast-cancer cells to proliferate fast enough to gain the upper hand over
the body's defences.

"Melatonin is a layer of protection that you have at night," Dr. Blask said.
"When you have enough light present to suppress it, you lose -- you
eliminate -- that layer of protection."

What you can do
Researchers who study the health effects of artificial light at night say
there is one commonsense way to minimize exposure: Spend a reasonable amount
of time at night in continuous darkness.
This allows your body to generate high levels of melatonin, the hormone
secreted by humans at night that limits the growth of breast cancer and may
help slow other tumours.

Russell Reiter, a professor of neuroendocrinology at the University of Texas
in San Antonio and an authority on melatonin, said almost everyone in
industrialized countries lives too much of their time at night under
electric light bulbs and is consequently melatonin-deprived, in contrast to
people living in a more natural environment.

"It's alarming in the sense that this may be a major . . . [contributing]
factor for the incidence of breast cancer and maybe other cancers," he said.

Dr. Reiter recommends that after you go to bed, avoid turning on lights if
you wake up. If you go to the washroom at night and turn on a light, this
tricks your body into thinking it is daytime, causing melatonin production
to cease. "One second of light in the middle of the night is too much," he
said.

He said the general glow of lights over cities at night is probably not a
health hazard. But as an additional safety precaution, some researchers
recommend that you make sure your bedroom is as dark as possible.

Melatonin is produced by the brain's pineal gland when you are in darkness
at night, and has nothing to do with how long you sleep. The crucial factor
is to remain in darkness for as long as possible, whether you are asleep or
awake, according to Richard Stevens, an epidemiologist at the University of
Connecticut.

Dr. Stevens has conducted research showing that the amount of time a woman
spends in darkness causes a change in breast-cancer risk. Those in darkness
for nine or more hours a night have a lower risk than those in darkness for
only seven or eight hours.

It is only the blue part of the light spectrum that stops people from
producing melatonin. Dr. Reiter said light bulbs could be redesigned to
eliminate the frequency causing blue light, allowing lights to be used at
night without harming melatonin production.

Melatonin is available in supplements, but experts are divided on its use as
an anti-cancer therapy. Dr. Reiter predicts it will become more widely used
for this purpose.

But Dr. Stevens recommends that because the human body produces melatonin,
you should do things to maximize the amount your body makes. "If melatonin
is important, live a melatonin-friendly lifestyle."


















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