Findings About Parkinson's Disease: Coffee and Hormones Don't Mix

Several large studies have shown that caffeine intake is associated
with a reduced risk of developing Parkinson's disease (PD) in men,
but studies in women have been inconclusive. A new study shows that
hormone therapy is a possible explanation for the different effects
of caffeine on PD risk in men and women.

From the National Institute of Neurological Disorders and Stroke :

New Findings About Parkinson's Disease: Coffee and Hormones Don't Mix

Thursday, April 17, 2003

Overview Several large studies have shown that caffeine intake is
associated with a reduced risk of developing Parkinson's disease (PD)
in men, but studies in women have been inconclusive. A new study
shows that hormone therapy is a possible explanation for the
different effects of caffeine on PD risk in men and women.

Several large studies have shown that caffeine intake is associated
with a reduced risk of developing Parkinson's disease (PD) in men,
but studies in women have been inconclusive. A new study shows that
hormone therapy is a possible explanation for the different effects
of caffeine on PD risk in men and women.

"We hoped to find something that would explain the effect of caffeine
on PD risk in men and the lack of an effect in women," says lead
author Alberto Ascherio, M.D., Dr.P.H., of the Harvard School of
Public Health. "Hormones seemed like a possible factor in this case."

Ascherio and his colleagues found combining coffee and hormones
significantly increases women's risk of developing PD, even though
each factor alone has previously been found to protect against PD.
The study shows that postmenopausal women who took hormone
replacement therapy (HRT) and drank more than five cups of coffee per
day (heavy coffee drinkers) were one and a half times more likely to
develop PD than heavy coffee drinkers who didn't take HRT.

Taking coffee out of the equation, HRT seemed to have a protective
effect against PD; these results support those of earlier studies.
Women who drank little or no coffee and took HRT had 65 percent less
risk of developing PD than light coffee drinkers who didn't take HRT.
The study was funded in part by the National Institute of
Neurological Disorders and Stroke and appears in the March 11, 2003,
issue of Neurology.1

The researchers studied survey data from more than 77,000 nurses who
participated in the Nurses' Health Study, a comprehensive 20-year
study designed to take a closer look at women's health.2 One hundred
fifty-four women in this group were diagnosed with PD during the
study. Overall, there was no difference in disease incidence between
women who were and weren't using HRT. However, when caffeine
consumption was factored in, HRT made a big difference in PD risk.

Among women taking HRT, the increased risk of PD was confined to
women who drank more than five cups of coffee per day. Drinking small
amounts of coffee per day did not appear to affect the risk of PD in
these women. Women who did not take hormones who drank less than half
a cup of coffee per day had a PD risk similar to that of men, Dr.
Ascherio says.

The type of hormones and the duration of use did not seem to affect
outcomes. The researchers note that they controlled for possible
effects of cigarette smoking, which has repeatedly been shown to be
associated with a decreased risk of PD.

Dr. Ascherio says these results could explain the inconsistencies
researchers have seen in the caffeine-PD association in women. He
says it also lends further credibility to the argument that caffeine
may have a protective effect against PD. "Now we know that when you
take hormones out of the equation, caffeine has the same effect on
women as it does in men," says Dr. Ascherio. "To me, this is very
compelling."

While this study may help researchers build a more solid case for
caffeine's relationship with PD, women should not read too much into
it. "Women should not change their habits or stop taking hormones
because of this study," Dr. Ascherio says. "We need more studies so
we can take a closer look at the relationship and mechanisms
involved.Â"

Researchers say that while caffeine is clearly associated with PD in
some way, they lack convincing evidence that caffeine actually
prevents the disease. "Association does not equal causality," says co-
author Michael Schwarzschild, M.D., Ph.D., of Harvard Medical School
and Massachusetts General Hospital.

The mechanism by which caffeine affects PD remains a riddle. In
animal models, researchers have shown that caffeine can prevent the
loss of dopamine-producing nerve cells seen in PD, but researchers
still don't know how this occurs. Dr. Schwarzschild says the
protective effect could be related to caffeine's ability to block a
particular receptor in the brain. How such a blockade might protect
nerve cells remains unknown, he adds.

The effect of estrogen on the relationship between caffeine and PD is
even harder to explain. "There are several possible explanations, all
of which need to be tested," says Dr. Schwarzschild. Estrogen is
known to have neuroprotective effects in PD, so there is a chance
that estrogen and caffeine are competing and therefore canceling out
each other's effect, he says. Another theory is that estrogen could
in some way interfere with how caffeine is broken down in the body.
To begin testing these theories, researchers are now studying whether
the protective effects of caffeine differ in male and female animal
models.

Dr. Ascherio stresses the need to confirm the findings of this study
in larger prospective studies of PD in women.

Many other researchers continue to probe the complex differences in
PD risk between men and women. In a recent study appearing in the
March 2003 issue of the journal Movement Disorders,3 researchers at
the Mayo Clinic in Rochester, Minnesota found that environmental
factors may play a greater role in the development of PD in men than
in women, and that genetic factors may have a greater influence on
the disease in women than in men.

The researchers suggest that more men, especially of older
generations, have been exposed in the workforce to environmental
factors, such as pesticides, industrial chemicals and head injuries.
On the other hand, they found that women require a stronger genetic
susceptibility to develop PD. The researchers also affirmed previous
findings that estrogen reduces the risk of developing PD. The Mayo
Clinic study was also funded in part by NINDS.

The NINDS is a component of the National Institutes of Health in
Bethesda, Maryland, part of the U.S. Department of Health and Human
Services, and is the nation's primary supporter of biomedical
research on the brain and nervous system.

References:

1Ascherio A, Chen H, Schwarzschild MA, Zhang SM, Colditz GA, Speizer
FE. "Caffeine, postmenopausal estrogen, and risk of Parkinson's
disease," Neurology, March 11, 2003, pp. 790-795.

2Colditz GA, Manson JE, Hankinson SE. "The Nurses' Health Study: 20-
year contribution to the understanding of health among women,"Journal
of Women's Health, 1997; vol. 6, pp. 49-62.

3Maraganore D, de Andrade M, Lesnick TG, Farrer MJ, Bower JH, Hardy
JA, Rocca WA. "Complex interactions in Parkinson's disease: A two-
phased approach." Movement Disorders, April 2003; vol. 18, Issue 4;
online early view at http://www3.interscience.wiley.com/cgi-
bin/fulltext/104084206/FILE?TPL=ftx_start.

- By Tania Zeigler

Reviewed April 17, 2003

SOURCE: ScienceBLOG
http://www.scienceblog.com/community/article1504.html

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