Monday, December 1, 2008


There is quite a bit of info on melatonin, our hormone that makes us sleepy. For more info, search or

Below, I am just going to include the bits of info on melatonin relevant to breast cancer because I find this quite interesting.

When I asked why melatonin is prescribed for breast cancer, I was told many people with breast cancer have irregular circadian rhythms or sleep-wake cycles.

For over 4 years now, I have had broken sleep due to being pregnant and getting up for babies through the night. Even though Grace is now 3.5yrs and Lily is nearly 2yrs, I still get up to check that they are covered up and are not cold, once or twice a night. It is now just habit!

I leave a night security light (outside light not night light for kids) on and the light shines into our room. Some nights, I get up and turn it off because it is not dark enough to sleep.

I sit and work on my computer most nights until about 10 or 11pm otherwise I never get to touch my work as the kids are always around. The screen is quite bright and maybe it inhibits the production of melatonin that occurs around this time.

Goodness knows how much I upset my circadian rhythms in my clubbing days....!!


Production of melatonin by the pineal gland in the brain is inhibited by light and permitted by darkness. For this reason melatonin has been called "the hormone of darkness" and its onset each evening is called the Dim-Light Melatonin Onset (DLMO). Secretion of melatonin as well as its level in the blood, peaks in the middle of the night, and gradually falls during the second half of the night, with normal variations in timing according to an individual's chronotype.

Until recent history, humans in temperate climates were exposed to only about six hours of daylight in the winter. In the modern world, artificial lighting reduces darkness exposure to typically eight or fewer hours per day all year round. Even low light levels inhibit melatonin production to some extent, but over-illumination can create significant reduction in melatonin production. Since it is principally blue light that suppresses melatonin, wearing glasses that block blue light in the hours before bedtime may avoid melatonin loss.

Melatonin levels at night are reduced to 50% by exposure to a low-level incandescent bulb for only 39 minutes, and it has been shown that women with the brightest bathrooms have an increased risk for breast cancer.

Reduced melatonin production has been proposed as a likely factor in the significantly higher cancer rates in night workers, and the effect of modern lighting practice, including light pollution, on endogenous melatonin has been proposed as a contributory factor to the larger overall incidence of some cancers in the developed world.