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December 20, 2005

Artificial Light At Night Stimulates Breast Cancer Growth In Laboratory Mice (Updated with links)

Topics: Medicine


Evidence is emerging that disruption of one's circadian clock is associated with cancer in humans, and that interference with internal timekeeping can tip the balance in favor of tumor development.

Melatonin exerts a strong influence on the body's circadian rhythm, an internal biological clock that regulates sleep-wake cycle, body temperature, endocrine functions, and a number of disease processes including heart attack, stroke and asthma. It also shows potential oncostatic activity and is acutely suppressed by light exposure. Some evidence suggests an association between night work and breast cancer risk, possibly through the melatonin pathway.

Researchers have already shown that a modestly elevated risk of breast cancer exists in humans after longer periods of rotating night work. Now, results from a new study in laboratory mice show that nighttime exposure to artificial light stimulated the growth of human breast tumors by suppressing the levels of melatonin. The study also showed that extended periods of nighttime darkness greatly slowed the growth of these tumors.

The study results might explain why female night shift workers have a higher rate of breast cancer. It also offers a promising new explanation for the epidemic rise in breast cancer incidence in industrialized countries like the United States.

Additional Links:
Circadian disruption and breast cancer: from melatonin to clock genes.
Therapeutic Role Of Melatonin In Cancer Worthy Of Study
Modulation by melatonin of the cardiotoxic and antitumor activities of adriamycin.
Melatonin and Cancer Treatment

Posted by Richard at December 20, 2005 6:22 AM

This post was of particular interest. My little sister died from breast cancer. She was a registered nurse later becoming a certified nurse practitioner. Worked "rotating" shifts at the emergency room in the hospital. When I think of her positions she's worked in artificial light I'd say about 25+ years. She died at 47 with breast cancer. Mary--->23Sept1948-25Sept2004. Still brings tears to my eyes. Who knows.......maybe the light thing is real.

If I could post her picture here I would. Her face looks as if she's not ill at all but in reality she's got the monster inside her. Started in one of her breasts. Chemo and treatment halted it for awhile. But it came back and was found in her liver. She battled and fought bravely for 2+ years. 1 out of 7 women have breast cancer.

To all women.............take care of yourselves.

Posted by: dr_usa_23 at December 20, 2005 2:57 PM


I'm very sorry to hear about your sister. Unfortunately, the "melatonin effect" has been known for many years, is well researched and documented, but not well publicized. In fact, it's known that physiological and pharmacological blood concentrations of melatonin inhibit tumorigenesis in a variety of in vivo and in vitro experimental models of neoplasia, and has also been shown to reduce the risk of death in cancer patients.

It is wise to take supplemental melatonin if either working night shifts or alternating shifts. It is also wise for cancer patients or patients recovering from cancer to supplement their diet with melatonin, usually taken one hour before bedtime.

You might find [] useful.

Any cancer is a tough row to hoe, and of course there are no assurances that any particular action or treatment will be successful. Sometimes we just run into a particularly aggressive cell type under conditions of optimal growth. Although we are learning more every day, and survival rates are now increasing, some of us just have a tougher time than others.

Again, I'm very sorry to hear about your sister, but she is not alone among night shift workers having to deal with cancer - the light effect is very real...

Posted by: Richard at December 20, 2005 3:44 PM

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