Women who slumber with the light on or stay up late could increase the likelihood of getting breast cancer, so say scientists .
Too much light at night upsets crucial hormones and ups the chance of developing breast tumours.
Those women who work at night like nurses as well as air stewardesses are especially at risk.
Scientists have shown that exposure to artificial light can be cancerous.
The American National Cancer Institute and National Institute of Environmental Health Sciences study explains the increasing levels of breast cancers in wealthy countries, where getting cancer is five times greater than in underdeveloped countries.
Breast cancer especially affects women in the UK, with 1 in 9 women being affected at some point.
Around 41,000 women are diagnosed each year and each month in the UK more than 1,000 die from the disease.
The study by American scientists showed that exposure at night to artificial light stimulated the growth of human breast tumours by suppressing the levels of the key hormone melatonin.
Melatonin, secreted by the pineal gland at night, assists in the regulation of a person's sleeping and waking cycles.
Light stops the body from producing it, rendering the body thinking that it is daytime.
Lighting manufacturers may be forced to develop more natural products, similar to natural day light.
Our 24-7 society of course does not help this process.
