Health and Sleep Survey of Blind Women

Health and Sleep Survey of Blind Women

The Braille Monitor
April
2005
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Health
and Sleep Survey of Blind Women

by Steven W. Lockley,
Ph.D.
From
the Editor: The NFB has agreed to work with Brigham and Women's Hospital and
Harvard Medical School to gather data that may shed light on breast cancer risk.
Here is the information:
Over
the past fifty years the incidence of breast cancer has risen dramatically in
the U.S. Similar increases have also been seen in countries that have recently
developed Western-style economies. The explanation for these increases is in
doubt, although family history, diet, medication, smoking, alcohol use, and
reproductive history can account for about 50 percent of the known risk. The
search for other factors associated with modern living that relate to breast
cancer risk is ongoing in order to identify those which are avoidable, which
can be altered by providing health and lifestyle advice to women.
One
notable factor in modern society is the use of artificial electric light, which
has eliminated much of our natural exposure to darkness. Light exposure at night
has effects on the human body such as stimulating the brain to be more alert
and changing the timing of the internal twenty-four-hour body clock. Light exposure
at night also stops the production of a hormone called melatonin, which occurs
only at night. Exposure to even room-level lighting is enough to stop melatonin
production, and brighter lights or longer exposure causes more suppression.
The effects of stopping melatonin production at night are unknown. Many animal
studies, however, suggest that melatonin may slow down growth, particularly
in breast cancer. Such studies have not been conducted in people, and the way
melatonin relates to cancer risk in humans is not known. If melatonin production
does affect cancer risk, we may expect several groups who are regularly exposed
to bright light for long durations at night to have more cancer. Based on this
theory, several U.S. and European studies have investigated female shift workers
who are exposed to light at night and have found a 36-60 percent increase in
breast cancer risk in women working night shifts regularly over many years.
Similar findings have been made in surveys of female flight attendants who are
also exposed to light at night when traveling across time zones.
The
theory suggests that women who are not exposed to light at night may be at a
reduced risk of breast cancer. This hypothesis has been examined in several
studies of cancer risk in visually impaired women. These studies have shown
that visually impaired women are at a reduced risk of breast cancer compared
to sighted women and that reduced risk is related to the severity of visual
impairment: totally blind women are least at risk and have about 50 percent
of the risk of the sighted population. One potential explanation for this finding
is that totally blind women have more melatonin, which protects them against
cancer risk. So far, however, several small studies have not found their melatonin
levels to be any higher than those of the normal population, although larger
studies need to be performed to test this idea fully. There are also many other
possible explanations for why totally blind women appear to be at a reduced
risk, for example differences in diet, drug and alcohol use, or reproductive
history.
But
one possible cause of cancer development is the twenty-four-hour body clock--circadian
system--which controls the timing of many biological processes, including the
cell. Because they lack light perception, over half of totally blind people
cannot maintain their body clocks on a twenty-four-hour day and, as a result,
suffer from cyclic sleep disorders. The possible role of the circadian system
in cancer development is an area of active research and may also be found in
shift workers and flight attendants, who have problems remaining synchronized
to the twenty-four-hour day.
In this month's issue
of the Braille Monitor Brigham and Women's Hospital
and Harvard Medical School in collaboration with the NFB are beginning a nationwide
survey of health and sleep in visually impaired women aimed at addressing why
blind women appear to have less risk of developing breast cancer. If the factor(s)
reducing risk can be identified, this information can provide health and lifestyle
advice for all women, not just visually impaired women, to reduce their risk
of developing breast cancer.
If you are interested
in assisting with this study, consult the miniature describing it in detail
in the "In Brief" section.
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