A plethora of studies have been published in recent months linking inadequate sleep to obesity, diabetes and stroke. Now, a recent review by the American Medical Association found research that suggests disruptions of the circadian rhythm due to nighttime light could also play a role in the risk of breast cancer, as well as of ovarian, prostate and colorectal cancers.

The work of University of Connecticut cancer epidemiologist Richard G. Stevens, PhD who first proposed in the late ‘80s a link between the use of artificial light at night with the high breast cancer risk in the industrial world, and others is officially being acknowledged by the AMA.

Stevens, professor in the UConn School of Medicine Department of Community Medicine and Health Care, had a major role in writing the report, “Light Pollution: Adverse Health Effects of Nighttime Lighting.” The AMA’s House of Delegates voted to accept recommendations from this report presented by the AMA Council on Science and Public Health. According to UConn Today, the council addresses “changes in lighting technologies and usage, recognition of the impact on sleep and sleep disorders, and further study of the possible link between light at night and cancer risk, obesity, and exacerbation of chronic diseases such as diabetes.”

The AMA’s recognition of the growing body of evidence that exposure to artificial light and disrupted circadian rhythms are associated with a myriad of health problems may result in more government funding in this area of research.

“There’s no question that this light at night changes our physiology in the short term,” Stevens says in UConn Today. “We know that artificial light disrupts circadian rhythms. We’re learning more and more about the specifics of what that means. The clearest evidence is about the hormone melatonin. We’re lowering it, we’re even suppressing it completely, depending on the amount of light.”

Melatonin is the hormone that regulates our cycles of sleep and wakefulness. According to StatesmanJournal.com, the council cited in its report to the AMA that melatonin “may exhibit a number of anticancer effects on cells, such as suppressing the proliferation of cancer cells.”

Its production is inhibited by light exposure at night, so people working in artificial light at night may have lower melatonin levels. In 2007, the International Agency for Research on Cancer, the cancer arm of the World Health Organization, added overnight shift work as a probable carcinogen.

Scientists suspect that overnight work harms the body because it disrupts the circadian rhythm, the body’s biological clock. Melatonin, which is normally produced at night, can suppress tumor development.

Stevens was among the first to spot the night shift-cancer connection in 1987. Since then, several studies have found that women working the night shift for many years were more prone to develop breast cancer.  Some research points to a link between men working the graveyard shift and higher rates of prostate cancer.

Sleep deprivation may be another risk factor for cancer. People who are sleep-deprived have a weaker immune system and are less capable of fighting off potentially cancerous cells.

“Night shift people tend to be day shift people who are trying to stay awake at night,” said Mark Rea, director of the Light Research Center at Rensselaer Polytechnic Institute in New York.

Anyone whose light and dark schedule is often disrupted — including insomniacs and frequent lengthy travelers— is potentially at increased risk of cancer, Stevens said in USA Today in 2007.

Animals that have their light-dark schedules switched also develop more cancerous tumors and die earlier.

“The balance between light and dark is very important for your body,” Stevens said, advising workers to sleep in a darkened room when they get home from work. “Just get a dark night’s sleep.”

Disrupted light and dark schedules also have been shown to negatively affect metabolism, mental acuity and behavior. Science Daily reports on a study where, after six weeks of being kept in 20-hour light/dark cycles, mice “got fatter, showed less mental flexibility and were more impulsive than mice kept on their natural schedule.”

Mice experienced accelerated weight gain and obesity, changes in their metabolic hormones and degradation of the neurons in the prelimbic prefrontal cortex, “a brain region important in executive function and emotional control.”

According to lead researcher Ilia Karatsoreos, the circadian rhythm acts as a web, with rhythms at the molecular level driving rhythms at the cellular level, which affect rhythms at the tissue level. “This can lead to a cascading set of effects throughout the whole organism,” she said.

Researchers believe this cascade can affect how humans respond to challenges to the metabolic or immune systems, such as high fat food or infection. They are especially concerned with the effects on the peripheral tissues involved in metabolism and energy usage, such as the liver and the adipose tissues.

Of his own most recent studies, Stevens is quick to point out that while associations have been found between artificial light, circadian disruption, melatonin suppression and breast cancer, no causal relationship has been established. “A reasonable jury would say there is a preponderance of evidence, but it’s not beyond a reasonable doubt at this point,” he says.