Newsletter #61-September/October 2000
What Light Through Yonder Window Wreaks-Circadian Rhythms and Breast
Cancer

by Sharon Batt

It was the opening session of a workshop exploring the effect that
artificial light has on breast cancer risk, and University of
Connecticut epidemiologist Richard Stevens showed an aerial slide of
the United States by night. Dots of white city lights twinkled against
the blackness, coalescing into splotches in areas of high population
density.

The pattern recalled maps showing the geographical distribution of
breast cancer rates, with the high-incidence areas along the northeast
coast, the Great Lakes' boundary, and in the coastal cities of
California.1 The image neatly captured the hypothesis that participants
would consider for the next two days at the conference ("Circadian
Disruption as Endocrine Disruption in Breast Cancer," sponsored by
the National Action Plan on Breast Cancer): that artificial light at
night is a type of pollution that contributes to breast cancer.

The hormone melatonin is produced at night and regulates circadian
rhythms, our daily wake-sleep patterns. Give people melatonin
supplements and they nod off. Artificially reverse light and dark, and
melatonin production switches accordingly; so do sleep rhythms. As we
age, calcium deposits accumulate in the pineal gland, which produces
melatonin-and some researchers suspect that both melatonin levels and
hours of sleep may be diminished as a result.

Melatonin has cancer-fighting properties. Seventy-five percent of
cancer shows oxidated DNA damage. Melatonin rivals vitamin C in its
ability to counteract the oxidating effects of estrogen and radiation.

The discovery that the pineal gland actually secretes something dates
only to the 1970s, but this hormone of darkness is ancient. Species at
all evolutionary levels, from algae to moths to humans, secrete
melatonin at night. Nature tripped these circadian switches until a
century ago, when Thomas Edison invented electric light. We in the
industrialized North can now choose from 15,000 sources of artificial
light to shorten our long winter nights.

"If light were a drug, I'm not sure the Food and Drug
Administration would approve it," Charles A. Czeisler quipped in the
Medical Tribune last year. Even tiny slivers of light at night disrupt
the melatonin levels of rats, promoting tumor growth. Removing the
pineal gland in rats stimulates tumor growth, and melatonin inhibits
the growth of estrogen-receptor-positive (ER+) breast cancer cells in
vitro by 30 to 40 percent. This leads researchers to speculate that
reducing our exposure to light at night might decrease rates, and that
pharmacological use of melatonin may be effective in treating cancer.

Research Findings

Josephine Arendt, a professor at the Centre for Chronobiology in
Surrey, England, became interested in melatonin after she was diagnosed
with breast cancer 19 years ago. Her work illustrates the difficulty of
testing hypotheses with real-world studies. Comparing blood serum
melatonin levels of sighted individuals living in the United Kingdom
with those of blind people and inhabitants of parts of Antarctica where
the sun does not rise at all for three months, Arendt found no
significant differences. Two studies of profoundly blind women have
found lower breast cancer rates, as predicted, in this population; a
third study did not.

Arendt also found no differences between melatonin levels in women with
benign and malignant breast tumors (an American study has found a
difference). Since melatonin levels diminish with age, Arendt stresses
that epidemiological research should control for this variable. Small
pilot studies are inherently limited but, as Arendt observes, "these
studies are not cheap, and it's hard to get funding for a large,
prospective study with negative pilot data."

Epidemiologist Richard Stevens, meanwhile, points to a study that found
elevated breast cancer rates among Finnish flight attendants, noting
that the incidence is too high to be accounted for solely by increased
radiation exposure. Disruption of circadian rhythms might well be a
causative factor in these cancers, he says. And alcohol disrupts sleep,
which in turn could suppress melatonin, perhaps explaining why
excessive alcohol consumption increases breast cancer risk.

Windows of Time

William Hrushesky, M.D., a clinical researcher at the Stratton VA
Medical Center in Albany, New York, believes that research on cycles
should extend beyond circadian rhythms to menstrual and seasonal
cycles. We already know, he points out, about certain "windows of
time" that can optimize the effectiveness of cancer therapy while
reducing side effects. Cancer drugs should be administered in the
morning, when bone marrow and gut proliferate at two to three times the
nighttime rate. In a study of women with ovarian cancer, optimal timing
of chemotherapy improved efficacy from 11 to 44 percent. Performing
breast surgery in the early luteal phase of the menstrual cycle (days
14-21) yields a 25 percent advantage in ten-year survival over surgery
in other phases, he says, while mammography screening is less effective
in the luteal phase. (The day menstrual bleeding begins is considered
the first day of the cycle.) Pap smears for cervical cancer are more
sensitive during the summer, Hrushesky says, and breast cancer is most
often diagnosed in the spring.

"We are doing great harm because we ignore cycles," he charges. His
work has been ridiculed and ignored, he says, because of inertia and
linear thinking in the research community. Although five prospective
studies on the timing of breast cancer treatments are now in progress,
he predicts that only one, an Italian study, is properly designed to
yield meaningful results.

Translating the Data

While little of the research that exists on circadian rhythms is
definitive and can be translated to real-world practice, some lends
itself to an approach based on the best-available evidence. The good
news is that starlight, moonlight, and lightning all fall outside the
spectrum of light that depresses melatonin. Researchers speculate that
the body is made aware of lighting not through vision but through
another system in the retina-so if your bedroom window is next to a
street light, eye shades or a light-tight blind are harmless ways to
keep the melatonin flowing. Red-spectrum light is least disruptive and
therefore best for night lights or clocks with illuminated time
displays; blue-green light is most disruptive.

For advocates, research into circadian rhythms offers plenty of scope
for action. Melatonin is a product that can't be patented, which
suggests why research into its therapeutic potential is so sluggish.
Also, circadian rhythms lie outside the realm of much of cancer
research, so proposals are more apt to flounder. Finally, as William
Hrushesky argues, we need to put hard-won knowledge about "windows of
time" to better use.

For me, the National Action Plan on Breast Cancer's workshop recalled
an early radicalizing experience, a 1991 conference at which
Congressional representative Pat Schroeder blasted cancer researchers
for excluding women from clinical trials. Because women's cyclical
physiology doesn't fit the linear shoe of fashionable science, she
charged, "they even used male rats to study breast cancer."
Finally, a critical mass of researchers is saying that cycles matter.

Sharon Batt currently holds the Nancy Ruth chair in women's studies
at Mount Saint Vincent University in Halifax. She is the author of
Patient No More: The Politics of Breast Cancer (Gynergy Books, 1994)
and cofounded Breast Cancer Action Montreal.

1 See the National Geophysical Data Center's Web site
(www.ngdc.noaa.gov). Click on "DMSP Data Archive," then on "City
Lights at Night," which will link you to a map showing nighttime
lights around the world.

http://www.bcaction.org/Pages/SearchablePages/2000Newsletters/Newsletter061A.html