Just what you needed: another thing to stress about when you’re pulling an all-nighter finishing that big assignment. Scientists have reported a correlation between working during the night-time and a higher risk of developing breast cancer.
Dr. Julia Knight, a professor studying breast cancer at U of T’s Department of Public Health Sciences, is investigating this link. Knight explores the roles that melatonin and circadian rhythms (our day-and-night sleep cycle) play in breast cancer, which can afflict males as well as females.
Melatonin is a sleep hormone in humans that can be likened to a rechargeable battery. Darkness recharges melatonin levels, filling the “battery” with energy. When the body is exposed to light, melatonin levels gradually drop, eventually contributing to the force that drives us back to sleep.
With a strong anti-oxidant and immune function, melatonin has evolved in all plants and animals over millennia. With the use of outdoor and indoor night lighting, light pollution could be having a negative effect on both human and animal circadian rhythms, not to mention our health.
Some evidence indicates a higher cancer rate among shift workers who don’t spend enough time in the dark during a 24-hour period. In fact, one study suggested that exposure to light during the typical night period is a significant factor in the increased occurrence of breast and colorectal cancers in the developed world. Excessive light exposure leads to low melatonin levels in the blood, which may be linked to certain cancers.
“Melatonin-low blood has been observed in patients who develop breast cancer,” Knight explained, but whether low melatonin in the blood is a cause of the cancer or a symptom has yet to be shown.
Previous studies showed that airline crews, who work scattered hours with random daylight exposure, were more prone to breast cancer than people who work regular daytime hours and sleep at night. Following up on this work, Knight measured light exposure, exercise and diet in relation to melatonin.
Knight explained that subjects kept a journal during the study, where they entered specific information about light exposure, physical activity and medication. She also measured light concentration in the subjects’ environments.
Knight hypothesized that both daylight and artificial light affect melatonin levels, and could help predict a person’s risk of developing breast cancer, but her investigation proved inconclusive.
Her experiment did determine that physical activity has a direct relationship with breast cancer: the more you exercise, the less chance you have of getting the cancer. Knight is not discouraged by her experiment’s unclear results. She said she would continue refining her study of the link between light and breast cancer.
“The methods for measuring light and when in life to measure it could have been the major flaw,” she said.
She plans to join Dr. Mark Rea, of New York’s Lighting Research Institute at Rensselaer Polytechnic Institute, in future studies. These studies will have subjects wearing a new light metre resembling a headset, which more accurately records the intensity of light viewed by the wearer.
The links connecting light exposure, exercise and cancer may be important in treating and lowering rates of breast cancer.
