A new analysis of data from the Cancer Prevention Study II Nutrition
Cohort, including more than 143,000 men and women, has shown a
reduced risk of Parkinson's disease (PD) associated with moderate to
vigorous exercise.

No protective effect was seen with light exercise such as walking,
the researchers, with first author Evan L. Thacker, from the Harvard
School of Public Health, in Boston, Massachusetts, noted.

Parkinson's disease is now thought to result from the confluence of
multiple genetic, environmental, and behavioral factors, Thacker
told Medscape in an interview. "The field of PD research is moving
in the direction of trying to understand multiple factors at the
same time, and hopefully this kind of work can be helpful from that
perspective. It's 1 piece of the puzzle."

These findings will be presented at the 59th Annual Meeting of the
American Academy of Neurology (AAN) and are among several studies
released prior to their presentation by the AAN.

Multiple Risks

Three previous prospective studies with designs similar to this
study have suggested that exercise may be related to a reduced risk
for Parkinson's disease, Thacker noted. "What our study adds to
what's already been done is that we have a large number of cases —
over 400 PD cases, so that's a lot of information to work with," he
said. In addition, this cohort included both men and women; only 1
of the previous studies had included women.

In this study, the researchers prospectively followed 63,348 men and
79,977 women in the Cancer Prevention Study II Nutrition Cohort from
1992 to 2001. Physical activity was estimated at baseline from the
reported number of hours per week on average spent in light-
intensity and moderate to vigorous activities.

Light-intensity activities, averaging 3.5 metabolic equivalents
(METs), included walking and dancing; moderate to vigorous
activities, averaging 4 to 7 METs, included jogging or running, lap
swimming, tennis or racquetball, bicycling (or using a stationary
bike), and aerobics and calisthenics.

Over follow-up, there were 413 incident cases of PD, confirmed by
the treating physicians or medical record review. Rate ratios for PD
were estimated using proportional hazard models and adjusting for
age, sex, smoking, and other risk factors.

"Overall, risk of PD declined at high levels of physical activity,"
the authors write. Compared with participants who reported no
physical activity, those with the highest quartile for recreational
activity — for men more than 25 MET-hours per week, for women
greater than 18 MET-hours per week — had a reduced risk for PD.

Risk for Parkinson's Disease in Subjects in Highest Quartile of
Recreational Activity vs No Activity
End Point Rate Ratio 95% CI P
Parkinson's disease risk 0.8 0.6 – 1.2 .07


When light activity and moderate to vigorous activity were
considered separately, only moderate to vigorous activity was
associated with the reduced risk for PD, the authors note. "Light
activities like walking don't seem to make any difference at all for
whether people get Parkinson's disease, but for the more vigorous
activities — lap swimming, jogging, running, those kinds of things —
people who participated at the highest level have about a 40% less
risk of Parkinson's compared with the people who didn't do any
activity or only walking or light activities," Thacker said.

Risk for Parkinson's Disease in Subjects in Highest Quartile of
Moderate to Vigorous Recreational Activity vs No or Light Activity
End Point Rate Ratio 95% CI P
Parkinson's disease risk 0.6 0.4 – 1.0 .02


The results did not vary significantly by gender and were similar
when they lagged exposure by 4 years.

However, they found no significant relationship between recreational
activity at age 40 and PD risk. "If exercise truly does provide some
protection against Parkinson's disease, the protection may be
relatively short-lived," Thacker said in the AAN statement. One of
the previous studies had shown activity in early adulthood was
related to reduced PD risk, "so the jury's still out on this one,"
he said.

The mechanism connecting exercise and Parkinson's disease risk has
not been extensively studied to date in humans, Thacker said.
However some animal work has suggested that exercise may increase
levels of certain nerve growth factors and urate, both of which
might have protective effects. However, he said, "it's really too
early to say for sure what the biological link may be — it requires
a lot more work."

An interventional trial of exercise to provide definitive evidence
that it prevents PD would be difficult, he noted, but in the
meantime, "considering all of the other benefits of exercise, it
certainly doesn't hurt to make sure you get some moderate or
vigorous exercise several times a week."

The study was supported by grants from the National Institute of
Neurological Disorders and Stroke and National Institutes of Health.

American Academy of Neurology 59th Annual Meeting: Abstract SO3.006.
April 28 – May 5, 2007.



April 26, 2007 —
Susan Jeffrey
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