More on artificial light/melatonin and prostate & breast cancer

[Guest guest]

Maybe It's Better To Stay in the Dark

By Rob Stein

Washington Post Staff Writer

Tuesday, February 17, 2009; Page HE01

Might exposure to artificial light at night increase a man's risk for

prostate cancer? An unusual international study indicates that it might,

providing provocative new evidence that disrupting the body's natural

rhythms may play a role in one of the most common malignancies to afflict

men.

The first-of-its-kind study, which involved analyzing satellite measurements

of nighttime light emissions and cancer rates in 164 countries, found that

nations that emit the most light at night tend to have the highest prostate

cancer rates.

While the findings do not prove a cause-and-effect relationship, they follow

earlier studies that found men who work the graveyard shift appear to have a

higher risk of prostate cancer.

" This study is a very important new piece of evidence, " said G.

s of the University of Connecticut Health Center in Farmington, who

helped the conduct the study. It appears in the current issue of the journal

Chronobiology International. " The fact that we are seeing a strong

relationship lends plausibility to a real cause-and-effect. "

Although more research is needed to confirm the relationship, s and

others say enough evidence has accumulated to consider taking steps to

reduce unnecessary exposure to light at night.

" There is certainly no need for panic, " said C. Brainard, director of

Jefferson University's Light Research Program in Philadelphia, who

was not involved in the new research. " But since there's concern and a

growing weight of evidence, prudent avoidance would be advisable. "

How light might increase the risk for prostate and other cancers remains

unclear. But a key factor may be the hormone melatonin. Melatonin plays an

important role in regulating the body's natural rhythms, falling during the

day and rising at night. But when people are exposed to light at night, it

interferes with that pattern, causing melatonin to plummet. In addition to

regulating the body clock, melatonin suppression may affect levels of other

hormones, such as testosterone and estrogen, which can fuel prostate and

breast cancer. Melatonin suppression may also suppress the immune system.

Women who have jobs that expose them to light at night -- such as shift

workers or flight attendants -- appear to have higher breast cancer rates,

and a handful of studies have produced similar findings for men and prostate

cancer.

Laboratory studies have also found that human breast and prostate cancer

cells grow more slowly when exposed to melatonin in petri dishes, and human

breast and prostate tumors implanted in rats grow faster when the animals'

melatonin is suppressed by light exposure.

" Put this all together and it argues pretty strongly that light-induced

melatonin suppression may be at the heart of this, " said Blask, a

professor of structural and cellular biology at Tulane University.

In fact, enough evidence has accumulated that the World Health

Organization's International Agency for Research on Cancer concluded in 2007

that shift work was " probably carcinogenic, " with the strongest evidence

being for breast and possibly prostate cancer.

" This new study fits in with that, " said Blair of the National Cancer

Institute, who helped prepare the agency's evaluation.

The possible negative effects of too much light at night makes sense given

that for most of human history people were exposed to far fewer hours of

light, s said.

" Once we got fire, and then the electric light bulb was invented, things

really started to change, " said s, who published a study last year

with colleagues in Israel on the relationship between light at night and

breast cancer.

For that study, the researchers analyzed satellite measurements of nighttime

light levels in neighborhoods throughout Israel. After taking into account

differences in the neighborhoods that might explain variations in cancer

rates, such as wealth, ethnicity and average number of children, the

researchers found no link between night lighting and lung cancer. But the

researchers found that localities with higher night lighting had higher

breast cancer rates.

The new research for the first time applies the same technique on an

international scale to examine prostate cancer. The association between high

nighttime light emissions and high prostate cancer rates remained even after

researchers conducted statistical analyses to account for other factors that

might explain the findings by examining differences in gross domestic

product, electricity consumption and urban population density.

On average, the countries with the highest nighttime light emissions had a

prostate rate of about 157 cases per 100,000 men, compared with about 67 per

100,000 among the countries with the lowest nighttime light emissions. The

United States, which has among the highest nighttime light emissions, has a

prostate cancer rate of about 125 cases per 100,000. Bangladesh, which has

the lowest nighttime light emissions, has less than one case per 100,000.

" It's remarkable, " s said.

There was no association between light and lung or colon cancer, which

strengthens the case because those cancers are not believed to be related to

hormone levels.

If a cause-and-effect relationship is proven, a number of steps could be

taken to try to minimize the effects of light exposure at night. Light

toward the blue spectrum appears to have the most impact on melatonin, so

replacing light systems with those that emit light more toward the red end

of the spectrum could help, s said. Some communities have started

designing street lamps that direct more of their light downward so they

shine less in residents' windows, for example, s said.

s and others recommend that individuals take such small steps as

making sure they sleep in a fully darkened room and minimize their light

exposure if they do wake up in the middle of the night.

" When you go to the bathroom in the middle of the night, don't turn on that

big bank of lights on the vanity. We know that's enough to start lowering

your melatonin, " he said. " Instead, just have a dim red bulb in the bathroom

as a night light. It's enough to see, and it won't affect your melatonin. "

While Blask and others recommend taking melatonin supplements, s and

others recommend against that.

" Some people say, 'Just take a melatonin pill.' But taking a tablet could

disrupt your normal circadian rhythm, " s said. " What's much better is

get an adequate amount of dark time. Rather than taking a pill as a quick

fix, try making your lifestyle more consistent with where we came from. "

[Guest guest]

Night shift work is just part of my reality, and I have found relief

intermittently using melatonin when I am about to start a series of

night shifts, and when I am starting to go back to a normal day/night

schedule. I use 3mg about 1-5 times a month. NIH has basic

information on evidence and safety. Consumer Lab has info on quality

melatonin brands. My MD knows I take it, and it's a good idea to talk

with your PCP if considering it.

http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-melatonin.html

http://www.consumerlab.com/reviews/Melatonin_Supplements/melatonin/

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> Maybe It's Better To Stay in the Dark

>

> By Rob Stein

> Washington Post Staff Writer

> Tuesday, February 17, 2009; Page HE01

>