Cancer Decisions® - Sleep, Melatonin & Cancer (Light at Night: Part
II)
http://www.cancerde
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',
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-
Pukkala E, Ojamo M, Rudanko SL, Stevens RG, Verkasalo PK. Does incidence
of breast cancer and prostate cancer decrease with increasing degree of
visual impairment. Cancer Causes Control. 2006;17:573-
Wilson BW, Wright CW, Morris JE, et al. Evidence for an effect of ELF
electromagnetic fields on human pineal gland function. J Pineal Res.
1990;9:259-269.
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