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The focus of the National Heart Foundation Heart Week, the first week
of May, is physical activity and heart disease. This is timely given
recent evidence that inactivity is a major risk factor for coronary
heart disease (CHD), and that the population risk attributable to
inactivity appears to be similar to the risk posed by smoking, raised
lipid levels or hypertension.1,2
The evidence
- Much of the epidemiological evidence relates to primary prevention
and comes from good-quality observational (cohort) studies. The
better-designed studies show stronger relationships and a
dose-response relationship between inactivity and CHD; the
benefits of increasing activity levels accrue particularly for
people who have been inactive.1
- Evidence from meta-analyses suggests that people who remain
sedentary have about twice the risk of CHD of those who participate in
regular activity.3 Replication studies in
diverse populations since 1990 have reinforced this evidence.
- There is consistent evidence that women benefit almost as much as men
from regular, moderate-intensity physical activity, as do older
adults.4,5 It appears that only
recent or current physical activity is beneficial, rather than
athleticism in earlier life.6 For all age groups, adopting
physical activity reduces the risk of CHD deaths, leading to the maxim
that "it is never too late to start being active".5,7
- Some of this cardiovascular benefit occurs even at levels of
physical activity below those required for aerobic (fitness or
cardiorespiratory) training, at levels as low as 50% of the maximal
predicted heart rates for age.1,8 However, for the general
population, more vigorous activity results in additional benefits.
- There is also evidence that physical activity may prevent ischaemic
stroke.9 The mechanism may be through
reducing the risk of thrombus formation, or the effects of physical
activity may be mediated through reducing blood pressure levels.
- These protective effects reducing the incidence and mortality from
CHD are independent of the influence of physical activity on other
cardiovascular risk factors. Nonetheless, there are direct
benefits on other risk factors, with moderate activity contributing
to lowered blood pressure, increased high density lipoprotein (HDL)
cholesterol level, and improvements to the fibrinolytic
system.1,8 More sustained physical
activity may also help with weight loss.
- Physical activity has similar benefits for many patients with
established coronary artery disease. In those who become active,
these benefits include increased fitness, improved oxygen
consumption, and decreases in ischaemic responses.8
Biological mechanisms: Researchers have begun to explore the
biological mechanisms to explain the benefits of physical activity
in preventing CHD. There is controlled-trial evidence that
sustained vigorous activity can lead to some regression of
atherosclerosis.8,10 Exercise may improve
coronary endothelial-dependent vasodilatation responses,
possibly leading to recruitment of collateral vessels in ischaemic
heart disease.11 However, further work is
needed to define the exact biological mechanisms. For patients with
CHD, there is clinical evidence of increased functional capacity and
improved myocardial perfusion after exercise training, and there
may even be some benefits for those with uncomplicated heart
failure.8
Cardiac rehabilitation: Although the benefits of cardiac
rehabilitation are generally accepted,12 these are multifaceted
programs, and the individual benefits of the exercise component are
difficult to disentangle from the overall program benefit. The key
issue here is that, after myocardial infarction, a much higher
proportion of patients in Australia need to complete supervised
rehabilitation programs than is currently the case.
Risk of acute cardiac events: One well-known paradox is the issue of
the increased risk of acute cardiac events in unfit sedentary people
who embark on vigorous exercise regimens.13 Although the risk of
sudden cardiac events is transiently increased (during and for a half
hour after strenuous exertion), this acute increment in risk is much
reduced for moderate activity. Overall, even among CHD patients, the
long term benefits of activity vastly outweigh the short term risks.
Furthermore, it has been shown that the overall risk for primary
cardiac arrest is much lower among those who are moderately
active.14 Thus, among cardiac
patients, vigorous activity should be started with caution and in
supervised settings, whereas moderate physical activity should be
easier to initiate.
In conclusion, almost half of Australian adults do not achieve the
health goal of moderate participation in physical activity. Recent
trends have shown that physical activity levels are declining (as
obesity rates are increasing), and that women, those least
advantaged and non-English speakers are more likely to be
inactive.15 There is a clear mandate to
include physical activity advice in consultations, especially for
those at risk of heart disease. Brief advice about activity,
delivered in the surgery, can positively influence physical
activity levels.16 Adherence to structured
activity programs is poor, so that constant reinforcement is useful,
as well as recommending types of activity which can become part of
everyday life. Some patients will be very active, but still develop
CHD. However, on balance, increasing activity is a worthwhile
investment of medical practitioners' time. For Heartweek 2001, go
for a regular walk, and recommend it to almost every patient!
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