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The Night Shift and Breast Cancer

Posted 10/23/2006

For years, doctors have puzzled over why women who work the night shift are more likely to get breast cancer. Now they think they’ve come up with an explanation, and it has to do with melatonin–the same melatonin sold to promote sleep.

Melatonin is a hormone made by the tiny pineal gland in your brain. (For years, doctors had no idea what the pineal actually did. In fact, early anatomy books named it “the seat of the soul.”)

Your brain responds to darkness by producing more melatonin, which in turn makes you sleepy. When you’re in bright light, either natural or artificial, your brain makes less melatonin. If you ever wondered why you fall asleep in a dark theater or wake up when sun pours into your bedroom, now you know.

As a side note, melatonin is made from serotonin. Logically then, women with low-serotonin Triple Whammy disorders often have more problems sleeping.

Melatonin is also an extremely powerful antioxidant, and has even tested well in lab animals in high doses as cancer therapy.

Some recent research looked at the melatonin-breast cancer connection. Doctors injected human breast cancer cells into rats. The cells “took” and started to grow. Then they injected the rats with one of two types of blood, the first from women with very low melatonin levels and the other from women with high melatonin levels.

The growth of the cancer cells in rats given the high-melatonin blood was dramatically suppressed, while cancer cells in the rats that got low-melatonin blood continued to grow. The provisional conclusion: melatonin can suppress the growth of breast cancer cells.

Many women working the night shift don’t ever experience total darkness, and thus their melatonin levels never get particularly high. It’s this lack of melatonin production that may be the basis for their increased breast cancer risk.

A couple of important cautions:

  • Even if you’re a poor sleeper, you’re still making melatonin as long as you’re in the dark (i.e., breast cancer risk is not higher among insomniacs).
  • It’s too early to recommend taking melatonin as a supplement to prevent breast cancer.

However, melatonin is a safe and effective sleep aid and a potent antioxidant. If you happen to work the night shift, it may be a prudent addition to your daily supplements.

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