Breast Cancer Mystery Frustrates Scientists: Electric Light Just Latest Of Many Suspects

The University of Connecticut cancer epidemiologist says there still is no scientific consensus about why the incidence of the disease is so much higher in the developed world.

The literature on breast cancer is littered with discredited theories about environmental and lifestyle factors that may contribute to the onset of the disease.

"We knew more about the cause of breast cancer 20 years ago than we do today," Stevens said. "What we do know is that it must have something to do with industrialized society."

Only a few theories have withstood scientific scrutiny, and no single factor explains a great percentage of breast cancer cases.

Now, Stevens and a few other researchers are focusing on a little-known suspect - electric light.

Their theory that artificial light can cause breast cancer is simple. Prolonged periods of exposure to artificial light disrupt the body's circadian rhythms - the inner biological clocks honed over thousands of years of evolution to regulate behaviors such as sleep and wakefulness. The disruption affects levels of hormones such as melatonin and the workings of cellular machinery, which can trigger the onset of cancer, Stevens theorizes.

"Mankind has only been exposed to these light sources for 150 years or so," Stevens said.

So far, the theory is based largely on suggestive, but inconclusive, observational studies. For instance, night-shift workers such as nurses tend to be more prone to develop breast cancer than day-shift workers, and blind women are less likely to have breast cancer than women with sight.

In a recent study, Stevens and scientists at Yale University School of Medicine identified a possible genetic mechanism that could help explain how artificial light could trigger breast cancer. Pre-menopausal women with a variation of a "clock gene," which helps govern the regulation of the body's response to night and day, tend to have a higher risk of cancer.

"I'm not saying this is a cause, but that the evidence shows it is worth investigating," Stevens is quick to caution.

The fact that the origins of breast cancer still are being debated - and that new theories are emerging more than three decades after the United States declared a war on cancer - illustrates just how stealthy breast cancer is.

Scientists estimate that about nine out of 10 breast cancer cases are triggered by environmental and lifestyle factors rather than inherited risk. Smoking has long been identified as a cause of lung cancer, and a virus, human papillomavirus, causes cervical cancer.

But with breast cancer, researchers are not sure what lifestyle or environmental causes women should worry about.

Some widely circulated theories have little data to support them and have been largely rejected by the scientific community. Antiperspirants and wire bras fall into this category, according to the National Cancer Institute. In 2003, the institute convened 100 breast cancer experts who concluded there is no evidence that miscarriages or abortions increase the risk of breast cancer.

Yet epidemiologists such as Stevens say other risk factors must exist and they urge that more studies be conducted.

"We absolutely need studies," said Deborah Winn, chief of the clinical and genetic epidemiology research branch of the National Cancer Institute. "If we have those answers, we might have the potential to improve prevention."

While the number of deaths from breast cancer has declined over the years, the incidence of the disease has increased slowly over the decades in the developed world, most studies show. And when a woman from a low-risk country moves to a high-risk country, her risk of breast cancer increases as well.

That's why suspicion centered on factors such as diet or pollutants such as pesticides.

Scientists believed for years that high levels of dietary fat accounted for differences in the rates of breast cancer in the developed and undeveloped worlds. But fat has largely been exonerated in breast cancer, Stevens said. A recent study in the Journal of the American Medical Association showed that even a diet heavy on fruits and vegetables did not protect women from the disease. And while pesticides can cause cells in laboratory dishes to turn cancerous, they have never been conclusively linked in large-scale studies to clusters of breast cancer cases.

There are plenty of oddities in the breast cancer epidemiology studies. Obesity is a risk factor for women - but only after menopause. Prior to menopause, obese women tend to get breast cancer less often than thinner peers.

Science, however, does say with great certainty that at least one factor plays a crucial role in the development of breast cancer: the female hormone estrogen, said Dr. Melinda Irwin, assistant professor in the department of epidemiology and public health at the Yale University School of Medicine.

For instance, Irwin notes that girls who get their first periods early in life and women who enter menopause late in life - in both cases, increasing their exposure to estrogen - are clearly at greater risk of breast cancer than their peers. Women who give birth to children before the age of 30 have a lower risk of breast cancer than women who give birth after 30 and women who never become mothers at all. Women who take hormone replacement therapy are also at higher risk.

Irwin has also done research that suggests that exercise, which can lower estrogen levels, offers women some protection against the development of breast cancer.

But Stevens and others believe other elements of modern lifestyle and environment must play a role in increasing the risk of breast cancer.

In the mid-1980s, Stevens investigated connections between cancer and the use of electric power. The work helped set off a controversial debate over whether there was a link between electric power lines and the development of cancer. It got him thinking about the potential role of electric lighting.

For most of human history, people slept or rested during dark hours - and produced the hormone melatonin. Melatonin levels regulate circadian rhythms and may, some studies suggest, affect estrogen levels as well. Artificial light tends to disrupt those rhythms, with reduced levels of melatonin believed to lead to an increase in estrogen production.

The light theory of breast cancer has received a boost in recent years with the discovery of clock genes, a group of about eight genes that help regulate circadian rhythms. It turns out that clock genes play an important role in the activation of genes governing cell cycle regulation and apoptosis, or cell suicide. Malfunctions in these processes have been linked to the development of cancer.

Many scientists believe that the search for environmental and lifestyle triggers for breast cancer will not turn up one major villain, but many different culprits that account for small percentages of breast cancer cases.

"I think we will be hard-pressed to find a single etiology to breast cancer. A woman's body is so complex and exposed to so many different things," said Dr. Kristen A. Zarfos, assistant professor of surgery and medical director of the University of Connecticut Health Center Women's Specialty Health Program.

"It might be a combination of small effects of a lot of things we know about," Stevens conceded. "But if not, then what is it? It is frustrating that major drivers have just not emerged for breast cancer as they have for other major cancers."

I must respectfully disagree with you, sir. Human psychology is based on the fundamental wiring of the human central nervous system, and that is a constant across the species. It's my belief that people in every culture suffer equally stress from sorrow, fear, or loss; the flood that takes a child causes just as much rage, confusion, and stress to the simple, uneducated Bangladeshi woman as it would to a sophisticated, educated New Yorker, and the Bangladeshi is no more likely to move on with her life because of religious beliefs than the American. The difference is that the American has access to grief support groups, antidepressant medication, and psychotherapy that can help assuage her grief while the Third-World inhabitant does not, and must simply bear her pain. There is no recourse for the poor Pakistani woman if her husband beats her or her home is destroyed.

How do I know? I have befriended very humble people from impoverished Third-World nations like Bangladesh, Indonesia, the Philippines, Ghana, and Liberia. At first there's a tendency to think they're simple of mind and heart because they don't have sophisticated ways to express complex emotions. But get to know them and you'll find that their feelings and reactions are no less, no different from ours.

I do believe that our stresses are far less serious than those of people in the Third World, particularly as we have the security of knowing that we will not be allowed to die of starvation or disease, have access to recreation, have access to justice, and have only to work hard to achieve financial success. Worrying about college loans and career advancement is a pretty trivial stress compared to the question of whether one will live or die, or whether one's children will die before they're three.

I must respectfully disagree with you, sir. Human psychology is based on the fundamental wiring of the human central nervous system, and that is a constant across cultures. It's my belief that people in every culture suffer equally from sorrow; the monsoon that takes one's children causes just as deep and lasting grief, rage, confusion, and stress to the simple, uneducated Bangladeshi woman than it would to a sophisticated, educated New Yorker, and the Bangladeshi is no more likely to move on with her life because of religious beliefs than the American. The difference is that the American has access to grief support groups, antidepressant medication, and psychotherapy that can help assuage her grief while the Third-World inhabitant does not, and must simply bear her pain. There is no recourse for her if her husband beats her or her home is destroyed.

I do believe that our stresses are far less serious than those of people in the Third World, particularly as we have the security of knowing that we will not be allowed to die of starvation or disease. Worrying about college loans and career advancement is pretty trivial compared to the question of whether one will live or die, or whether one's children will die before they're three.

At first there's a tendency to think they're simple of mind and heart because they don't have sophisticated ways to express complex emotions. But get to know them and you'll find that their feelings and reactions are no less, no different from ours. ----Capriole.

I do not think they are simple of mind or heart at all. And by the way i am originally from those parts, so it would be kind of ridiculous for me to claim they are simple minded (and infact i think they are far better at dealing with things than most people in other cultures - with the exception of certain Asian cultures). They have different ways of working through stress. For example they have intense faith (and since you said you have befriended people from places like Ghana, the Philippines and so forth you know what i mean). Once something happens they grieve through it, and then they move on. This does not mean at all that they are simple-minded, just that they have a divergent archetype of working through stuff.

Totally agree with you. I even said that in my post. Most Western stress factors are absolutely trivial, especially when compared with what people in the rest of the world go through. And i also said that according to the medical field it is not the magnitude of stress but its constancy. The human body is, as i said before, able to cope with great deals of stress. What it is not made for is coping with perpetual levels of stress.

A person can be intensely stressed for a short-period of time, and even have psychosomatic symptoms as well as true-to-life physical illness. But normally the body rectifies that after a while. However have another person who is always stressed, even if it is over totally insignificant things, and the body soon gets basically overburdened.

People in the third world have big stresses (and again note that i am talkign of typical locales, not places like the Sudan that have constant and heightened levels of oppression/suppression/repression etc). In your typical developing nations there are huge life issues. For example if the rains are late then there is a chance the whole harvest is lost. Or if there is a malaria outbreak. Or some pathogen that blights that seasons crop yield. These are truly HUGE stress factors. But they are not constant. And most of the people from there are actually quite happy ....actually quite joyful (again, since you have met people from overseas you must have noticed remarkable levels of joy. It might not be termed as 'western happiness,' but is is joy beyond description).

In the west many (not all) people in urban areas have many small issues. Totally insignificant (for example many of my workmates always seem to be working under the Sword of Damocles - as if there is always a looming threat). The stresses may not be near that of an Indian facing crop shortage for his 4 kids, but the marking factor is that the stress is chronic. Always present. And that is what makes it dangerous.

But anyways, what do I know! Here is an excerpt on the medical significance of constant stress.

Time magazine's June 6, 1983 cover story called stress "The Epidemic of the Eighties" and referred to it as our leading health problem; there can be little doubt that the situation has progressively worsened since then. Numerous surveys confirm that adult Americans perceive they are under much more stress than a decade or two ago. A 1996 Prevention magazine survey found that almost 75% feel they have "great stress" one day a week with one out of three indicating they feel this way more than twice a week. In the same 1983 survey only 55% said they felt under great stress on a weekly basis. It has been estimated that 75 - 90 percent of all visits to primary care physicians are for stress related problems. Job Stress is far and away the leading source of stress for adults but stress levels have also escalated in children, teenagers, college students and the elderly for other reasons, including: increased crime, violence and other threats to personal safety; pernicious peer pressures that lead to substance abuse and other unhealthy life style habits; social isolation and loneliness; the erosion of family and religious values and ties; the loss of other strong sources of social support that are powerful stress busters.

Contemporary stress tends to be more pervasive, persistent and insidious because it stems primarily from psychological than physical threats. It is associated with ingrained and immediate reactions over which we have no control that were originally designed to be beneficial such as:

* heart rate and blood pressure soar to increase the flow of blood to the brain to improve decision making,

* blood sugar rises to furnish more fuel for energy as the result of the breakdown of glycogen, fat and protein stores,

* blood is shunted away from the gut, where it not immediately needed for purposes of digestion, to the large muscles of the arms and legs to provide more strength in combat, or greater speed in getting away from a scene of potential peril,

* clotting occurs more quickly to prevent blood loss from lacerations or internal hemorrhage.

These and myriad other immediate and automatic responses have been exquisitely honed over the lengthy course of human evolution as life saving measures to facilitate primitive man's ability to deal with physical challenges. However, the nature of stress for modern man is not an occasional confrontation with a saber-toothed tiger or a hostile warrior but rather a host of emotional threats like getting stuck in traffic and fights with customers, co-workers, or family members, that often occur several times a day.

Unfortunately, our bodies still react with these same, archaic fight or flight responses that are now not only not useful but potentially damaging and deadly. Repeatedly invoked, it is not hard to see how they can contribute to hypertension, strokes, heart attacks, diabetes, ulcers, neck or low back pain and other "Diseases of Civilization".

Today, provoked by our online debate, I broached this subject to about ten people in our office, medical professionals who have all been born and raised in different Third World countries. Interestingly, their views were rather monolithic, and they both agreed and disagreed with both of us.

They agreed with you that people in their homelands, wherever in the world those homelands are, are happier than most Americans. They seemed to believe that this was in part because their countrymen were not driving themselves mad in an ambitious effort to attain material success, but were contenting themselves with what was available locally. They did not expect the government to give them things or help them. And they were always surrounded by family and friends, from whom they could expect communal support. It is a mistake, they said (and I agree strongly with this) for children to leave home to go to college, pursue careers and raise children far from their roots; there is great comfort to be found in living close to kin.

They also agreed with you that Western diseases like hypertension are less prevalent, but also as medical workers they pointed out that many people in the Third World do not live long enough to develop circulatory disease. The typical Third World diet, through all its variants, does not offer enough richness to bring about coronary disease. There is also far more opportunity for exercise, as my 90-year-old relatives in rural Slovakia would agree. So it's difficult for these medical professionals to ascribe the low incidence of circulatory disease in their cultures to low stress levels, as correlation is not causation; there could be several interconnected reasons.

As for stress, they agreed that day-to-day living in the Third World causes little stress, particularly for men. But unfortunately most Third World countries, your own blessed homeland of course excepted, are subject to famines, shortages, war, terrorism, epidemics, etc. So 15 years of a peaceful agrarian existence will be interrupted by a five-year civil war during which thousands are killed, followed by a dictatorship, followed by an insurgency and refugee status, etc. This is an ongoing stress--but again, unpleasant as it may be, people do not live long enough to develop coronary artery disease from it. And life, they point out, is very different for Third World women than for men, as the women are often subject to a harder life than we in the West can imagine, with resultant depression and stress.

The bottom line is that it is not Third World life but agrarian life, whether in the undeveloped countries or in the US, that brings the most peace and satisfaction to people. Having lived on a large farm during my formative years, I know well the quiet joys and peace that can only come from living in the country. I intend to return there soon. Best of all is life in the rural USA, where modern conveniences and health care are combined with a quiet outdoor lifestyle!

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