Sleeping in darkness boosts breast cancer drug effectiveness

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New research suggests that the effectiveness of the breast-cancer drug tamoxifen could be affected by something as simple as sleeping with a light turned on. A recent study, published in the journal Cancer Research, has established a connection between the performance of the widely prescribed breast cancer drug tamoxifen and a patient's melatonin level. 


Researchers associated with the Circadian Cancer Biology Group at Tulane University School of Medicine sought to examine how melatonin levels changed the effectiveness of tamoxifen therapy. Sleeping with a light on, such as a dim lamp or television, can affect melatonin production because, depending on the light source intensity, light can penetrate the eyelid and strike the retina. The investigators exposed rats to light conditions simulating a day and night cycle. At first the rats were exposed to full darkness for 12 hours to simulate the “night” cycle, but they were also tested for exposure to dim light during the “night” period as well. Tumor growth was found to be slowed in test animals exposed to full darkness or dim light with supplemental melatonin. When higher levels of melatonin were present, more cellular pathways that support medication resistance are shut down and the tamoxifen is more effective. The researchers recommend taking tamoxifen just before bedtime, and encourage patients to sleep in dark conditions.


Sleeping in darkness boosts breast cancer drug effectiveness
Sleeping in darkness boosts breast cancer drug effectiveness

Keeping a light on at night can suppress the body's production of a hormone called melatonin, possibly reducing the effectiveness of the breast-cancer drug tamoxifen, a study suggests. 

The study published in the journal Cancer Research points to a connection between low melatonin levels and resistance to tamoxifen, a common breast cancer drug.

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