Should we all be using blackout curtains and eye shades at night? A new study, published in Chronobiology International, shows an unequivocal positive association between bedroom light intensity and increased risk of breast cancer.

NEW YORK – Friday, 7th January 2011 – Previous research on female night-shift nurses uncovered a link between to light-at-night (LAN) exposure in the workplace and risk of developing breast cancer.   Chronobiology International – the leading journal on biological rhythms and their importance to health and well-being – has unveiled the results of the first-ever study conducted to assess the link in women between habitual exposure during sleep to LAN in the bedroom, such as from night lights and television sets, and risk of developing breast cancer.

More than 1670 women took part in the 10-year study – titled Breast Cancer in Northern Israel - conducted by the University of Haifa.
Light-at-night, or LAN, exposure from sources outside and within households – specifically in the bedroom due to night lights and sleeping with TV on -- plus availability of shutters in the bedroom -- was evaluated.

The bedroom LAN level of exposure, which was evaluated using a four-point scale: from completely dark (1) to strong light, i.e., all bedroom lights switched on (4), emerged as significant predictor of breast cancer. 

Controlling for education, alcohol, number of pregnancies and ethnicity, habitually sleeping with LAN in the bedroom was found to increase the risk of break cancer by 22% compared to the control group -- women who were not routinely exposed to LAN during night-time sleep in their bedroom.

This link to breast cancer is thought to arise from light waves in the blue color range emitted from outdoor energy-saving high-intensity and fluorescent lamps as well as regular and energy-saving bedroom-light sources.  LAN suppresses the body’s normal night-time production of melatonin (MLT), a hormone produced in the pineal gland of the brain only during the darkness of the night and which acts not only modulates estrogen levels but acts directly as a first-line of natural defence against cancer.

“The findings of this study highlight the importance of MLT in modulating estrogen levels in relation to breast cancer,” says Abraham Haim, Professor at the Israeli Center for Interdisciplinary Research in Chronobiology at the University of Haifa, and co-author of the study.

Suppression of MLT by LAN has been found to increase estrogen level, which could be related to increased risk of breast cancer. Due to its disruptive effects on circadian rhythms, night work done under LAN is already widely recognized as a significant risk factor for breast cancer, but this is the first time a link has been shown between bedroom LAN during night-time sleep and the disease.
“Accelerating urbanization worldwide and rising living standards have meant that electricity has become more accessible and affordable for wide segments of the population, resulting in increased LAN exposure both within peoples’ houses and in the streets outside their windows,” continues Professor Haim.

In the past decade, electricity consumption and LAN intensity has increased markedly with the introduction of new lighting sources which include the modern outdoor high-intensity discharge (HID) and fluorenscent lamps that emit blue wavelengths – believed to strengthen the LAN-Breast Cancer association.

“The novelty of the present study lies in the fact that this is the first large-scale, case-control study of the general population which has identified a significant positive association between bedroom light and ambient nighttime light – or light pollution - levels with breast cancer risk,” says Professor Michael Smolensky, Editor of Chronobiology International.

“This study provides evidence that the relative risk of breast cancer appears to increase in more illuminated sleeping environments, leading us to conclude that the modern human sleeping habitat with its high LAN levels can and should be considered a significant breast cancer risk,” continues Professor Smolensky.

“Beyond doubt, LAN is an integral part of our lifestyle and those levels will increase in the future,” explains Professor Haim. “Fortunately this is an environmental variable that can easily be controlled, thus reducing its health risk. Simple solutions exist, such as the installation of window blinds in the bedroom, and also by the use of eye covers while sleeping.”

-ENDS-

For further information, an interview with the author/s or editor or a PDF of the Chronobiology International article, please contact either: kirstin.stocker@informa.com or mary.drabot@informa.com