Moss: SLEEP, MELATONIN AND CANCER, Part II

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Cancer Decisions® - Sleep, Melatonin & Cancer (Light at Night: Part

II)

http://www.cancerdecisions.com/content/view/220/2/lang,english/

SLEEP, MELATONIN AND CANCER

Here are some more reflections on the fascinating " Circadian Disruption

and Cancer " conference that I attended at the New York Academy of

Sciences a few weeks ago.

There are a number of reasons to suspect that poor sleeping habits

contribute to an increased risk of breast or prostate cancer. Prime

evidence for this comes from a Norwegian study showing that totally

blind women have a decreased risk of breast cancer compared to sighted

women. The effect was only seen in the totally blind, as there was no

such protective effect from any degree of sight disability other than

total blindness.

Using Norway's large cancer registry, the authors identified 296 blind

women. Their incidence of breast cancer was just 64 percent that of

sighted women, i.e., there was a 36 percent protective effective. But

among those who went blind before the age of 54 (and therefore had lived

in total darkness for a longer period of time) the breast cancer

incidence ratio was just 0.51. In other words, their breast cancer risk

was half of the sighted women (Kliukiene 2001). That's an extraordinary

reduction, which sparked considerable discussion among researchers at

the conference.

" Our findings give support to the 'melatonin hypothesis', " the Norwegian

authors said. In other words, it supports the idea that the hormone

melantonin is protective against breast cancer. A Finnish study found a

similar effect among men with prostate cancer (Pukkala 2006).

Melatonin and Night

So what is this " melantonin hypothesis " of which the Norwegian speak?

Melatonin is a hormone naturally produced every day by the pineal gland,

which is located deep in the brain. Healthy young and middle-aged adults

generally secrete about 5 to 25 micrograms of melatonin each night. This

amount tends to decline with age, and this decline is possibly linked

with an age-related rise in sleep difficulties.

Melatonin is sometimes described as the sleep hormone, but this is not

correct. It is not geared to the sleep cycle, although it may help you

fall and stay asleep. It is produced in the dark, regardless of whether

or not the person is sleeping. Hence its name, which was coined in 1958

from the Greek word, 'melas,' meaning 'black.' Theoretically, you could

be up and about in the dark (such as listening to the radio) and still

produce the normal amount of melatonin.

At dusk, the decrease in sunlight sends a signal that stimulates the

pineal gland to produce more melatonin. Hormone levels then continue to

rise steadily for hours, peaking at around 2 a.m. (3 a.m. in older

people). It then declines sharply as morning approaches. By 8 a.m. or so

your melatonin levels are back down to their typical low daytime point,

only to start the cycle over again the following evening.

To be continued next week....

--Ralph W. Moss, Ph.D.

Resources:

Kliukiene J, Tynes T, Andersen A. Risk of breast cancer among Norwegian

women with visual impairment. Br J Cancer. 2001;84:397-399.

Pukkala E, Ojamo M, Rudanko SL, s RG, Verkasalo PK. Does incidence

of breast cancer and prostate cancer decrease with increasing degree of

visual impairment. Cancer Causes Control. 2006;17:573-576.

BW, CW, JE, et al. Evidence for an effect of ELF

electromagnetic fields on human pineal gland function. J Pineal Res.

1990;9:259-269.