Doctors have decided to act following clinical trials of blind women which showed they they have a significantly lower risk of developing breast cancer than fully sighted women.
The new research will explore the role of melatonin, a hormone produced during hours of darkness, in helping to prevent breast cancer.
Doctors are now convinced that breast cancer is a disease of industrialised nations, where rates are five times higher than in developing countries. They now suggest that one factor may be a 24-hour society with its artificial light which prevents Western nations from experiencing the total night- time darkness of many parts of non-industrialised countries.
Melatonin is thought to regulate the amount of oestrogen, another hormone in the body which they suggest may spur breast cancer. But the production of melatonin can be disrupted by artificial light, jet-lag and shift work. As a result, doctors are now to investigate whether this disruption allows oestrogen to build up in potentially dangerous quantities in the body's bloodstream.
The doctors, from the United States and Finland, stress that the findings so far are only circumstantial, that they have no direct proof of a connection and that women should not panic.
"This is not the moment for the public to become alarmed about exposure to artificial light," said Dr George Brainard, professor of neurology at Thomas Jefferson University in Philadelphia. "But it is the time for scientists to focus on the problem and establish whether this is a risk factor or not."
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