| Risking Life'
London, Dec. 1: Women who work night shifts are more likely to get breast cancer because their bodies produce far less of a vital hormone that inhibits the disease, according to research published today.
Scientists have demonstrated for the first time that human breast cancer tumours are suppressed when exposed to levels of melatonin produced during a normal night’s sleep. Tumours exposed to blood-lacking melatonin, from women exposed to bright light during sleep, were found to grow at roughly twice the normal speed.
The findings, published in the American journal, Cancer Research, provide the first proof of a biological mechanism to explain previous research showing that female night-shift workers have higher risks of breast cancer than those who work during the day, and studies showing that blind women have less chance of getting the disease.
Denis Henshaw, professor of human radiation effects at the University of Bristol, suggested that people concerned about the potential hazards of suppressed melatonin production could take steps to reduce their exposure to light at night.
Henshaw said: “If this paper is correct, measures could be taken to reduce exposure to light at night, such as for those people who live with a street lamp outside their house, use of heavy curtains.
“When people get up in the middle of the night to visit the bathroom, rather than turning on all the lights, they could survive on natural light or use low-wattage bulbs.
“The issue is more difficult for night-shift workers. We have moved over to a 24'7 way of working and one of the consequences of that is the killing-off of nocturnal melatonin production of those working at night.”
Melatonin is produced in the pineal gland in the brain when the body receives a signal that light levels have dropped below a certain level. Production can be curtailed if a person is exposed to bright light during the night.
Dr David Blask, from the Mary Imogene Bassett Hospital in Cooperstown, New York, and colleagues bred rats without immune systems.
They took blood from three groups of female volunteers ' those who gave samples during daylight hours, those who were sleeping in darkness, and those who were sleeping at night but who had been exposed to 90 minutes of bright light. Human breast cancer tumours were transplanted into the rats.
Injection of blood from those women who donated during daylight or who were exposed to light while they slept had no effect on the growth of the tumours. However, in the rats given blood from women whose samples contained normal levels of nocturnally-produced melatonin, breast cancer growth took roughly twice as long.
Melatonin-deficient blood that had synthetic melatonin added to it also suppressed tumour growth.