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Light at Night Affects Breast Cancer Treatment

breast cancer treatment

Strange as it may sound, the amount of light a woman is exposed to at night can have an impact on her breast cancer treatment. That is the finding of a team of researchers at Tulane University’s Circadian Cancer Biology Group, who observed this phenomenon in rats.

To better understand this relationship, it’s helpful to know all the players and their roles.

  • Light at night causes the body to stop its production of melatonin, a hormone produced by the pineal gland in the brain.
  • Melatonin helps regulate your sleep/wake cycle. Normally, levels of the hormone begin to rise during the evening hours, stay high for most of the night, and then decline during the early morning hours.
  • Tamoxifen is a commonly prescribed drug used for breast cancer patients. Researchers made a significant discovery about tamoxifen and light in this study

What researchers discovered

  • Melatonin alone can delay the development of tumors and have a significant impact on their growth
  • Rats given tamoxifen and who had high levels of melatonin associated with exposure to complete darkness at night demonstrated an important regression in breast cancer tumors
  • Rats given tamoxifen who were administered supplements of melatonin to keep their hormone levels high and who were exposed to light at night also demonstrated regression of breast cancer tumor growth

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However, rats given tamoxifen and who were exposed to light at night without melatonin supplementation showed resistance to the cancer drug. According to David Blask, one of the study’s authors, “when the lights are on and melatonin is suppressed, breast cancer cells ‘wakeup’ and ignore tamoxifen.”

The bottom line
The results of this study indicate that light plays a significant role in how effective tamoxifen can be in women who are being treated for breast cancer. This could mean, for example, that such women who work at night or who are around lighted television or computer screens at night (e.g., falling asleep with the TV on), or the use of night lights could make these patients resistant to tamoxifen.

In addition to sleeping in complete darkness, another possible solution may be to use melatonin along with tamoxifen in individuals who are being treated for breast cancer. This option as well as others will surely be the topic of future research into the impact of light at night on breast cancer treatment.

Tulane University

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