Cancer: Light & Dark

I'm trying to make sense out of two articles about the effect of artificial light at night on breast cancer rates. My friend C sent me a recent piece about this from the Chronicle of Higher Education; I'll post the article as a Comment. A better piece was in Science News. In short, the researchers say that in order to reduce your risk of breast and possibly prostate cancer:
-Sleep in a dark room and at night. More than nine hours is better than less.
-Stay away from foods with linoleic acid--which is rife in processed foods that contain corn syrup, corn oil, safflower oil and cottonseed oil. Linoleic acid helps tumors grow.
-Don't work the night shift. And if you do, don't raid the vending machines with your workmates because a lot of the packaged food in there is laden with linoleic.

Except. It's not that simple.

But first, the main idea: "'Breast tumors are awake during the day, and melatonin puts them to sleep at night," according to researcher David E. Blask, quoted in Science News. Another scientist says that you don't have to be asleep for optimum melatonin production, but you have to be in a dark room. From Science News: "Melatonin forms in the pineal gland, located in the brain, and circulates in the bloodstream. Blood concentrations of the hormone rise after dark from low daytime values and usually peak in the middle of the night." Studies have shown that women who work at night are more likely to have breast cancer, hypothetically because their melatonin levels are suppressed by light at night. In addition, a Finnish study showed that women who slept more than 9 hours a night were less likely to get breast cancer. And blind women have been shown to have less breast cancer than other women, and a "high average" level of melatonin.

Melatonin also keeps cancer cells from absorbing linoleic acid, which promotes cancer growth.
So, the experts say to sleep in a dark room. Blask does this himself and also takes melatonin supplements. Another researcher cautions people about taking melatonin because it's not regulated. But as a letter writer to Science News asked: "Are you really going to tell me you aren't going to take melatonin--if you're convinced that it might lower your chances of getting cancer by as much as 50 percent--because you are afraid of impurities?"

It seems that you could trade day for night, and get your melatonin from a dark room at midday. But that's difficult. "In theory, shift workers could swap their schedules completely and maintain a natural cycle of melatonin production during their sleep hours in the day, rather than the night," the Chronicle says, paraphrasing researcher Richard G. Stevens. "But most people who work during the night revert to a more typical schedule on their days off." Stevens tells Science News pretty much the same thing. Again, a paraphrase: "On their days off, most shift workers concentrate their activities during daylight, which upsets their circadian rhythms as much as commuting across several time zones would, he says." Does this disruption affect melatonin production? Apparently. But how? Nobody says.

And what if you sleep partly in the daytime but while wearing a blindfold, as some of our best Cancer Bitches do?

Scientists have been telling us lately that we're not getting enough Vitamin D because we've become so afraid of the sun. Now we're not getting enough dark. Again, a letter-writer asks a good question: "If the daily light-dark cycle affects melatonin, is there a seasonal change in cancer rates in the Northern (and Southern) Hemispheres?" I have my own question: Is there more cancer in the tropics?


Cancer Bitch said...

Chronicle of Higher Education.
From the issue dated June 29, 2007

Breast Cancer, Out of the Dark
Maverick researchers pursue the idea that lights at night increase the risk of a disease

Related materials
Graphic: Shining a Light on Cancer

Article tools


Discuss any Chronicle article in our forums

Three most recent discussions
Re: Jealousy

Today at 08:21:45 PM by malvolio

Re: Normative to the Sweat Lodge!

Today at 08:19:44 PM by realfrancie

Re: Grand America Hotel, Salt Lake City

Today at 08:19:44 PM by drstones

Richard G. Stevens saw the light one night — and it got him thinking about breast cancer.

While trying to sleep in his apartment in the mid-1980s, Mr. Stevens noticed that the street lamp outside was so bright he could almost read in his bedroom. "You couldn't do that a thousand years ago or even a few hundred years ago," he says. "People just don't experience dark anymore."

That observation sent his brain racing. As an epidemiologist, Mr. Stevens had been puzzling over a curious trend in breast-cancer statistics: The rates shoot up as societies grow more industrialized. Many other cancers — stomach, colon, and liver cancers — become less prevalent as a country modernizes, largely because people benefit from better sanitation and safer food. But epidemiologists could not figure out why breast-cancer rates in modernized societies were five times the levels documented in the developing world.

Maybe it was electric lights, reasoned Mr. Stevens as he lay awake that night. "One of the big changes in the industrialized world is light at night."

To many scientists, that hypothesis seemed nutty. Mr. Stevens, who is now an associate professor of epidemiology at the University of Connecticut School of Medicine, was originally warned off pursuing his ideas when he described them to his former mentor, the Nobel laureate Baruch S. Blumberg.

Ignoring that sage advice, Mr. Stevens jumped into researching the hypothesis, and his career suffered. But 20 years after he first published his suggestion, the concept is slowly gaining some support and his star is rising. "There was a long period of time where nobody was deeply interested," says George C. Brainard, a professor of neurology at Jefferson Medical College of Thomas Jefferson University, who studies light and its effects on the body. "Now the hypothesis has gathered weight behind it, and there are many people looking at it very seriously."

More than a dozen epidemiological studies indicate that women who work night shifts face a higher risk of breast cancer, perhaps because they are exposed to more light during nighttime hours.

Studies at the cellular level, meanwhile, are starting to reveal how light can enhance the growth of cancer cells. Normally tumors go to sleep at night because the body produces the hormone melatonin, which effectively shuts down the growth of cancer cells.

But recent studies have demonstrated that when women are exposed to light at night, their bodies don't secrete as much melatonin, and tumors can grow unchecked.

A Long Shot in the Dark

Mr. Stevens and his colleagues say they have a long way to go before they can determine whether light at night truly does raise the risk of cancer. "We're at the point where there is a strong circumstantial case," he says, "but it's not enough to convict."

Following this path of research has led him and his colleagues into the scientific wilderness, far from the topics that generate wide interest and financial support. Mr. Stevens has secured just one major grant to research the hypothesis, and, at age 56, is still without tenure. Others interested in the hypothesis have also struggled to get grants, and yet they have persisted with their work.

For some, it has been an obsession. Mr. Brainard started studying the biological effects of light when he was in high school in the 1960s, after reading an article in Life magazine that mentioned a lizard's pineal gland, a center in the brain that produces melatonin.

"Every time I had a chance to write a free paper in English class or any class," he says, "I wrote about pineal physiology and melatonin."

After college, when Mr. Brainard was working as a lab technician, his supervisor laughed at his idea of going to graduate school to study the pineal gland. "The feeling in science was that the pineal gland was active in lower species but not humans," said Mr. Brainard.

But evidence eventually started to accumulate that the pineal gland, through its production of melatonin, has profound effects in humans, helping to set the circadian rhythm, or biological clock. The system is regulated by light entering the eyes, where it generates a neural signal that heads to the pineal gland. During dark hours, the gland releases melatonin into the bloodstream. During the day, light absorbed by the eyes tells the gland to shut off the melatonin supply.

Mr. Stevens knew little about the melatonin system when he had his nighttime epiphany. But the sleepless musings sparked his curiosity, and he quickly boned up on pineal physiology. In 1987 he published "Electric power use and breast cancer: a hypothesis," in the American Journal of Epidemiology, one of the premier journals in the field. His hypothesis does not rule out that other elements of industrialization might play a role, it just suggests that lights are an important factor.

At roughly the same time, in a lab in Tucson, David E. Blask and his colleagues found evidence that supported the unconventional idea. Dr. Blask had started studying melatonin in 1968 as an undergraduate. In the latter half of the 1980s, his group at the University of Arizona produced a series of papers showing that normal biological levels of that hormone — the amount one might find circulating in the blood — inhibited the growth of breast cancer in cell-culture experiments.

Tumors at Light Speed

Since then, Dr. Blask has become the head of the lab of chrono-neuroendocrine oncology at the Bassett Research Institute, in Cooperstown, N.Y., with a joint appointment at Columbia University. In that lab, he and his colleagues have now developed much more sophisticated experiments that examine what effects light has on actual human breast-cancer tumors. Because it would be unethical to do such experiments on cancer patients, his group has developed a way to study this question indirectly, using rats that carry human tumors.

First, Dr. Blask and his team grow a human breast-cancer tumor from cells in a dish. They then implant the tumor under the skin of a rat, where it takes root. That experimental system allows them to test how the tumor reacts under different circumstances.

In one recent experiment, Dr. Blask collaborated with Jefferson's Mr. Brainard, who was studying how light altered the amount of melatonin produced by young women. Mr. Brainard's team took blood samples from the women during the day and during the night, while the women were kept in the dark. Then he took blood from the women after they had been exposed to relatively strong light for 90 minutes in the middle of the night.

Dr. Blask pumped those blood samples through the breast-cancer tumors growing inside the rats. The growth of the cancer cells slowed down when the tumor was fed blood taken from women in the dark. But the growth sped up when the tumor received blood taken during the day or taken after exposure to light at night.

The switch that controls the cancer's response appears to be melatonin. "During the day, cancer cells are awake and cranking along," he says. "Melatonin comes along at night and at its peak, the activity of the cells drops dramatically." The cells divided four times faster when fed by blood taken from women exposed to the light than they did with blood taken from women in the dark.

One way melatonin appears to work its magic is by protecting cells from a dietary danger called linoleic acid (which is not to be confused with linolenic acid).

In modest quantities, linoleic acid is a nutrient that our cells need for growth. But humans now consume many times more of this polyunsaturated fatty acid than they did in prehistoric times, says Dr. Blask. It appears in just about all processed foods, anything that has corn syrup, corn oil, safflower oil, or cottonseed oil.

"Vending machines, when you think about it — they are linoleic-acid bombs sitting there," says Dr. Blask.

When linoleic acid is ingested, it enters cancer cells and gets converted to a molecule that promotes the growth of the cancer cells. But Dr. Blask's experiments have shown that melatonin impedes this process by blocking the pathway that linoleic acid uses to get into the cells.

Melatonin may also protect people in other ways, by keeping cells from becoming cancerous in the first place, says Mr. Stevens.

But while the theory appears to work at the level of the cancer cell, epidemiologists have wondered whether light at night has any measurable effect on people's lives. Mr. Stevens set out to answer that question.

Risks in Night Shifts?

One population to examine, he suggested early on, would be women who worked night shifts, who would naturally get exposed to light throughout the night.

In theory, shift workers could swap their schedules completely and maintain a natural cycle of melatonin production during their sleep hours in the day, rather than the night. But most people who work during the night revert to a more typical schedule on their days off, says Mr. Stevens.

In one study, published in the Journal of the National Cancer Institute in 2001, Mr. Stevens and colleagues from the Fred Hutchinson Cancer Research Center, in Seattle, interviewed 800 women who had just been diagnosed with breast cancer. (They also interviewed 800 randomly selected women with no history of breast cancer as controls.) They found that night-shift work raised the risk of cancer by 60 percent in that sample.

Eva S. Schernhammer, an epidemiologist and assistant professor of medicine at Harvard University, has also studied the potential links between breast cancer and light at night. Dr. Schernhammer had a personal interest because she had started out her career as an oncologist in Austria, where clinicians at that time spent every third night on call.

When two young nurses working on the oncology ward at her hospital came down with cancer, that coincidence stuck with Dr. Schernhammer, and she later decided to investigate the potential cancer risks of night work when she went back to school to study epidemiology.

Dr. Schernhammer dug into data collected from more than 78,000 women participating in the long-running Nurses' Health Study, a large epidemiological project started by researchers at Harvard. She found a moderately increased risk among nurses who frequently worked the night shift.

Over all, more than a dozen studies have looked at shift workers, and almost all come to the same conclusion about the risks of heavy night exposure to light. "There is an emerging consensus in the cancer community that shift-working women are at an increased risk for breast cancer," says Mr. Stevens.

His hypothesis also predicted that blind women would be less susceptible to breast cancer, either because they do not turn on lights as often or because their impaired eyes do not transmit a signal to their pineal glands. To test that, Mr. Stevens worked with colleagues at the University of Helsinki, in Finland, in a study of 10,935 women there with visual impairment. The researchers found the exact relationship that they had expected: The worse a woman's visual impairment, the lower her risks of getting breast cancer.

So far only a handful of studies have examined that issue among blind women, and while they all support the link, the connection is weaker because the combined studies have included relatively few people, says Mr. Stevens. Epidemiologists like to see dozens of studies all pointing in the same direction before they become convinced of a relationship, he says.

Dr. Schernhammer says her colleagues believe "there is room to study this." But she doesn't think "the scientific community is that convinced that this is something that is going to be of major importance."

Is It Real?

Marilie D. Gammon is one of the skeptics. A professor of epidemiology at the University of North Carolina at Chapel Hill, Ms. Gammon ran a study in Long Island that found no association between breast cancer and women who had previously worked the night shift. "I think the epidemiological literature is inconsistent in supporting the hypothesis," she says, adding that the idea "is intriguing — it probably deserves more study."

Finding environmental triggers for breast cancer has proved particularly difficult, she says. And even when researchers find a solid link, they do not always know what to do with that knowledge. It took as many as 50 studies, she says, to demonstrate that drinking alcohol raises the risk of breast cancer. "But telling women to totally abstain may not be the best course, because we know that alcohol reduces the risk of heart disease, which is the bigger killer," she says.

The oddness of the light hypothesis alone makes it difficult for some to pursue this topic. "Most people, particularly cancer people, can't wrap their mind around the idea that light can affect [breast] cancer," says Dr. Blask, whose proposal to extend his study on breast cancer and light was recently turned down by the National Institutes of Health.

But prospects may be brightening for researchers studying light and cancer. Mr. Stevens will present the topic next month at a Gordon conference, a prestigious, invitation-only meeting. Then, in October, he and Dr. Blask will travel to France to help write a monograph on shift work and cancer for the International Agency for Research on Cancer.

Dr. Blask's newest work, in fact, suggests light might cause problems for men as well as women. At a meeting earlier this year, he presented data from a study of prostate-cancer cells, which shows they react to lowered melatonin levels in much the same way that breast-cancer cells do. Epidemiological evidence is also raising questions, as a recent study out of Japan found a correlation between night work and prostate cancer. The findings are intriguing, says Mr. Stevens, because prostate cancer is also increasing in the industrialized world, relative to its prevalence in developing nations.

The mess of data can make any resident of the modern world wonder what to do, short of putting on a blindfold the minute the sun goes down.

When pressed on the practical implications of their work, researchers who have studied this potential link say it is still too early to offer any prescriptions for action. No one knows yet, for example, whether falling asleep with the television on interferes with melatonin release.

Still, researchers working on the topic say they have changed their own habits. "You try to sleep in a dark room — it's as simple as that," says Dr. Blask. He takes melatonin supplements but does not advocate that others do the same. Although the supplements seem safe, he says, studies have not demonstrated that melatonin can prevent cancer. In keeping with his other research findings, he also tries to avoid the many kinds of processed foods that contain linoleic acid.

As for Mr. Stevens, he says, "I don't take melatonin. Oh no. No." Instead, he lives "a melatonin-friendly lifestyle."

That means going "to dark," if not to sleep, by 9:30 p.m. He says he eats fresh, wholesome foods and tries to get regular exercise.

And when he wakes up in the middle of the night, he doesn't turn on the light.


Cancer cells have a daily cycle. During the day, linoleic acid (a fatty acid found in many foods) enters cancer cells and promotes their growth. At night, the brain releases the hormone melatonin, which blocks linoleic acid from entering cancer cells. As a result, tumors grow more slowly at night, researchers say.

Section: Research & Publishing
Volume 53, Issue 43, Page A9

barbara said...

This is a terrific article, Sandi. I copied it and sent it to my brother. He's had prostate cancer for 10 years, and as an airline pilot, had an incredibly irregular sleeping schedule. As you know, he also has lung cancer. Had 5 tumors in his brain, but after radiation and chemo (3 Wednesdays out of every 4) for a few cycles, his oncologist called him a couple weeks ago and said that all the tumors are gone. So he's in remission of a sort, for a while, which is wonderful.

Garry Cooper said...

Well, I'm glad to see confirmation of what I've believed for some time: too much/too little light/dark, linoleic acid, and vitamin D causes/protects against cancer, and I have been taking steps to increase/limit my exposure/consumption. I am convinced that this will prevent/slow/cause the return of my cancer. I have also been snapping my fingers constantly to keep the elephants away, but unfortunately the excessive rubbing of thumb against middle finger has caused abrasions that look suspiciously like finger tumors.

Anonymous said...


In my experience, medical findings don't hold up under the strict scrutiny of logic. I know, it always seems like they should.

Anonymous said...

good, i just added tons of different emo backgrounds for my blog