MORE EXERCISE IS NOT ALWAYS BETTER
There is strong
epidemiological evidence of the importance of regular physical activity, such as
brisk walking and jogging, in the management and rehabilitation of
cardiovascular disease and in lowering the risk of death from other diseases
such as hypertension, stroke, and type 2 diabetes. The Physical Activity
Guidelines for Americans recommends about 150 minutes per week of
moderate-intensity exercise or about 75 minutes of vigorous-intensity exercise.
But there is clear evidence of an increase in cardiovascular deaths in heart
attack survivors who exercise to excess, according to a new study published in Mayo
Clinic Proceedings.
Paul T. Williams, PhD,
of the Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley,
CA, and Paul D. Thompson, MD, of the Department of Cardiology, Hartford
Hospital, Hartford, CT, studied the relationship between exercise and cardiovascular
disease-related deaths in about 2,400 physically active heart attack survivors.
They conducted a prospective long-term study using the National Walkers' and
Runners' Health Studies databases. This study confirmed previous reports
indicating that the cardiovascular benefits for walking and running were
equivalent, as long as the energy expenditures were the same (although when
walking, as compared to running, it will take about twice as long to burn the
same number of calories).
Remarkable
dose-dependent reductions in deaths from cardiovascular events of up to 65%
were seen among patients who were running less than 30 miles or walking less
than 46 miles per week. Beyond this point however much of the benefit of
exercise was lost, in what is described as a reverse J-curve pattern.
"These analyses
provide what is to our knowledge the first data in humans demonstrating a
statistically significant increase in cardiovascular risk with the highest
levels of exercise," say Williams and Thompson. "Results suggest that
the benefits of running or walking do not accrue indefinitely and that above
some level, perhaps 30 miles per week of running, there is a significant
increase in risk. Competitive running events also appear to increase the risk
of an acute event." However, they point out that "our study
population consisted of heart attack survivors and so the findings cannot be
readily generalized to the entire population of heavy exercisers."
In the same issue,
investigators in Spain report on a meta-analysis of ten cohort studies aimed at
providing an accurate overview of mortality in elite athletes. The studies
included over 42,000 top athletes (707 women) who had participated in a range
of sports including football, baseball, track and field, and cycling, including
Olympic level athletes and participants in the Tour de France.
"What we found on
the evidence available was that elite athletes (mostly men) live longer than
the general population, which suggests that the beneficial health effects of
exercise, particularly in decreasing cardiovascular disease and cancer risk,
are not necessarily confined to moderate doses," comments senior
investigator Alejandro Lucia, MD, PhD, of the European University Madrid,
Spain. "More research is needed however, using more homogeneous cohorts
and a more proportional representation of both sexes."
"Extrapolation of
the data from the current Williams and Thompson study to the general population
would suggest that approximately one out of twenty people is overdoing
exercise," comments James H. O'Keefe, MD, from the Mid America Heart
Institute in Kansas City, MO, and first author of an editorial on
"Exercising for Health and Longevity versus Peak Performance: Different
Regimens for Different Goals," which appears in the same issue. Along with
co-authors Carl "Chip" Lavie, MD, and Barry Franklin, PhD, he
explains that "we have suggested the term 'cardiac overuse injury' for
this increasingly common consequence of the 'more exercise is better'
strategy." Even so, these authors state that about 10 out of every twenty
people are not getting the minimum recommended amount of physical activity
(>150 minutes/week of moderate exercise).
O'Keefe, Franklin and
Lavie point out that a weekly cumulative dose of vigorous exercise of not more
than about five hours has been identified in several studies to be the safe
upper range for long-term cardiovascular health and life expectancy, and that
it may also be beneficial to take one or two days a week off from vigorous
exercise, and to refrain from high-intensity exercise on an everyday basis.
They propose that individuals from either end of the exercise spectrum
(sedentary people and over-exercisers) would probably reap long-term health
benefits by changing their physical activity levels to be in the moderate
range.
"For patients
with heart disease, almost all should be exercising, and generally most should
be exercising 30-40 minutes most days, but from a health stand-point, there is
no reason to exercise much longer than that and especially not more than 60
minutes on most days," says Lavie, who is a cardiologist at the John
Ochsner Heart and Vascular Institute, New Orleans, LA. "As Hippocrates
said more than 2,000 years ago, 'if we could give every individual the right
amount of nourishment and exercise, not too little and not too much, we would
have found the safest way to health.' I and my co-authors believe this
assessment continues to provide wise guidance," he concludes.
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