NEW YORK - A new study by the American National Cancer Institute and National Institute of Environmental Health Sciences says that women who are exposed to artificial light for long periods of time or stay up at night for a long time are at an increased risk for developing breast cancer.
Women who work night shifts are also thought to be at an increased risk. The new study demonstrated that artificial light increased the risk of developing breast cancer by inhibiting the levels of the key hormone melatonin. Melatonin is secreted by the pineal gland and this secretion takes place mostly at night. The hormone regulates a person's sleeping and waking cycles.
But the presence of light does not stimulate the production of the hormone. The researchers proved the theory by implanting human breast cancer cells in lab mice. Blood samples taken from women were injected into the mice. These samples were taken three times, during the day, in the early hours of the morning and at night after the women were exposed to artificial light.
The researchers found that the blood taken after dark appeared to slow tumor growth by 80 percent, but the blood taken after exposure to light appeared to stimulate the growth of cancer. "Evidence is emerging that disruption of a person's body clock is associated with cancer in humans, and that interference with internal timekeeping can tip the balance in favour of tumor development," said lead researcher Dr David Blask, adding that this was the first "proof that light is indeed a risk factor for cancer."
