Julia Knight, an epidemiologist and researcher at the Samuel Lunenfeld Research Institute at Mount Sinai Hospital in Toronto, is one expert pointing a finger at artificial light.
"Quite a few studies show that women who work rotating night shifts over a period of years are at an increased risk of breast cancer," she says. "One of the theories is that their exposure to bright, artificial light at night suppresses their melatonin."
Melatonin has been shown in both cell-culture studies and animal studies to be an anti-cancer hormone. During the day, levels are significantly lower, as they are in women who work nights. The only time melatonin levels rise is at night in the dark.
The link between low levels of melatonin and breast cancer is also supported by a study developed by Itai Kloog, a researcher in the department of natural resources and environmental management at the University of Haifa in Israel.
According to his research, the more lit up a settlement is at night, the higher the rates of breast cancer. Kloog explains that exposure to artificial lighting reduces the amount of melatonin the body produces, and this puts women at greater risk of developing breast cancer.
Melatonin stops growth of cancer
One of the more convincing studies of the influence of melatonin on cancerous tumours involved implanting human breast cancer under the skin of female rats. The researchers then took blood samples from several healthy, premenopausal volunteers.
The samples were collected under three different conditions: during the day; at night following two hours of complete darkness; and at night following 90 minutes of exposure to bright fluorescent light.
The blood samples were pumped directly through the developing tumours. The blood collected from the subjects in total darkness drastically slowed the growth of the tumours.
In contrast, the blood collected from the light-exposed subjects stimulated tumour growth. The researchers concluded that the results were due to the direct effect of the melatonin on the cancer cells.
Page 2 of 5 - Find out more about melatonin's effects on the body on page 3.
