Download Physical activity: the evidence of benefit in the prevention of

Q J Med 2003; 96:245–251
doi:10.1093/qjmed/hcg041
Review
QJM
Physical activity: the evidence of benefit in the prevention
of coronary heart disease
V. PRESS 1 , I. FREESTONE 2 and C.F. GEORGE 3
From 1Health Potentials, London, 2Sport England, East Midlands, and 3British Heart
Foundation, London, UK
Introduction
Over the past 40 years, evidence has accumulated
on the role of physical activity in preventing and
treating coronary heart disease (CHD). The findings
are consistent and show that sedentary people have
about twice the risk of developing or dying from
CHD, compared to active people. The evidence is
compelling and has established physical inactivity
as one of the major modifiable risk factors for CHD.
A recent analysis suggests that 37% of deaths from
CHD are attributable to physical inactivity; this is
second only to raised blood cholesterol.1 Despite
this, few doctors appear to realize the extent of the
benefits of regular exercise, nor are they aware of
current recommendations relating to it.2 This article
reviews the evidence for, and mechanisms by
which physical activity confers benefit, as well as
the main health messages and ways in which
people can be helped to become more active.
Throughout the paper, physical activity means
all activity at work and leisure, including sport.
Exercise means formal training-type activities,
which can also include sport.
Physiological benefits of exercise
The benefits of regular exercise include3 improvement in myocardial contraction and its electrical
stability, and an increase in stroke volume at rest
and during exercise, leading to a higher maximal
cardiac output. Heart rate is decreased at rest, and
at any given level of submaximal cardiac output.
Endothelial function is improved, leading to
better flow–mediated dilatation. In addition, the
diameter and dilatory capacity of coronary arteries
are increased, as is collateral formation. Regular
exercise also has effects on the tendency of blood
to clot. Changes include reduced platelet aggregation and increased fibrinolytic activity, possibly
resulting from lower levels of plasminogen activator
inhibitor-1. In addition, regular physical activity
lowers inflammatory factors such as plasma fibrinogen concentrations, C-reactive protein and white
cell count.
Metabolic adaptations include stimulation of
lipid oxidation during activity and in post-exercise
recovery.4 There are alterations in the transport of
blood lipids, with a higher ratio of high-density
lipoprotein (HDL) to low-density lipoprotein (LDL)
and increased lipoprotein lipase activity, which
increases the use of circulating triglycerides as fuel
and increases their clearance even at rest. Activation of this enzyme also speeds up the conversion
of the VLDL to HDL. Finally, regular exercise
improves the sensitivity of liver, skeletal muscle
and adipose tissue to the actions of insulin. Consequently, there are decreases in fasting insulin
levels and the insulin response to glucose, associated with increases in the disposal rate for
glucose.5
Given these highly favourable changes, it is
important to determine the level of exercise at
which these are manifest in a reduction of risk
factors and overall risk of CHD.
Address correspondence to Professor Sir C.F. George, British Heart Foundation, 14 Fitzhardinge Street, London
W1H 6DH
ß Association of Physicians 2003
246
V. Press et al.
The evidence that vigorous activity
prevents CHD
Vigorous activity is variously defined as expending
more than 6 mets or a minimum of 7.5 kilocal/min
or working at a minimum of 70% of maximum
heart rate or 70% of VO2max.6,7
Numerous studies have confirmed the benefits of
vigorous activity in reducing risk from CHD. The
Study of British Civil Servants by Morris et al. was
one of the landmark studies. A cohort of 17 944
male British civil servants (office workers) between
45 and 65 years of age and free of CHD were
studied prospectively. After 8.5 years of follow-up,
the age-standardized cumulative incidence of CHD
was 3.1% among men reporting vigorous exercise,
and 6.9% among those who did not.8 Many other
studies, most notably the Harvard Alumni Study,
have also shown that vigorous activity reduces the
risk of CHD.9
In 1985, as a result of the growing epidemiological evidence and physiological data, the
American College of Sports Medicine drew up a
recommendation, subsequently adopted internationally, that adults should take 20 min of vigorous
activity three times a week.10
The evidence that moderate
intensity physical activity prevents
CHD
Over the last ten years, there have been a growing
number of studies that show the benefits of
moderate intensity physical activity for cardiovascular health. Moderate intensity activity is variously defined as expending more than 6 mets or
approximately 5–7.5 kcals per min or exercising at
60–70% of maximum heart rate or at 60% of
VO2max.6,7 Practically, this means exercise that
makes the heart beat faster and breathing heavier,
but still allows talking. Examples are brisk walking,
swimming and cycling.
The British Regional Heart Study (BRHS) is a
large prospective study of cardiovascular disease
which began in 1978 involving 7735 men between
the ages of 40 and 59. Men with and without
pre-existing CHD were randomly chosen from the
age-sex registers of general practices in 24 British
towns. A standard questionnaire was completed
that included questions on leisure-time physical
activities (regular walking, cycling, sporting and
recreational activity) and other health habits.
Results of an 8-year follow-up demonstrated that
in men without pre-existing CHD those participating
in moderate or moderately vigorous activities had a
50% reduction in risk, compared to those who were
inactive.11 There was no threshold for benefit, with
rates of first heart attack declining with increasing
physical activity until the moderately vigorous
level. Men with pre-existing CHD showed a similar
inverse association up to moderate levels of activity.
There was no additional benefit seen in those
participating in vigorous activity.
Another 4-year follow-up study, beginning in
1992 and involving 4311 of the original BRHS men
(average age now 63 years) with no history of CVD
further demonstrated that all forms of mortality were
highest in the inactive group.12 The risk ratios
were: inactive/occasionally active group 1.0, light
activity group 0.61, moderate activity group 0.5
and moderately vigorous/vigorous activity group
0.65. There was also a significantly lower all-cause
mortality in men who were sedentary in 1978
but had taken up at least light activity by 1992,
when compared to those who remained sedentary
throughout. Physical activity improved both cardiovascular mortality (0.66) and non-cardiovascular
mortality (0.46), and the findings were similar for
men with pre-existing CVD. Similarly, reports from
the British Regional Heart Study have consistently
confirmed the health benefits of regular physical
activity for middle-aged men, and indicated that
the activity need not be vigorous but should be
regular and current in order to reduce cardiovascular
risk.
The Honolulu Heart Programme reported that
walking among elderly men was associated with
reduced risk of CHD. Data from 2678 physically
capable men aged 71–93 and free from CHD
showed that over a 2–4 year period, those who
walked -0.25 miles/day had twice the risk of CHD,
compared to those who walked )1.5 miles/day
(5.1% vs. 2.5%, p-0.01).13 Even those walking
0.25–1.5 miles/day were at significantly higher risk
Table 1 Summary of evidence of benefits of moderate
intensity physical activity on prevention of CHD
50% reduction in risk of CHD in men and women
without diagnosed CHD
Activity needs to be regular and current
Limited evidence that accumulation of several shorter
sessions of exercise gives the same benefits as one
longer episode
Lowers blood pressure in normotensive and hypertensive
people
Reduces risk of developing type 2 diabetes by 50%
Helps reduce overweight and obesity
Raises HDL and lowers triglycerides
Exercise and the heart
than those walking longer distances. The findings
were consistent even after adjustment for age and
other risk factors.
The Nurses Health Study, a large prospective
study of female nurses in the US, collected detailed
information on physical activity from 72 488
women aged 40–65 in 1986 and free from diagnosed CVD or cancer. After a follow-up period of
8 years, researchers examined associations between
total physical activity, walking and vigorous exercise and the incidence of coronary events.14 There
was a strong, graded inverse association between
physical activity and CHD risk. As compared with
women in the lowest quintile group for energy
expenditure, women in increasing quintile groups
had age-adjusted relative risks of 0.77, 0.65, 0.54
and 0.46 for coronary events (p for trend -0.001).
A similar pattern was found using multivariate
analyses. These findings indicate that both walking
and vigorous exercise are associated with substantial and similar reductions in risk of CHD. Women
who walked at least 3 h a week or exercised
vigorously for 1.5 h a week had 30–40% less risk of
CHD than sedentary women. Furthermore, those
women who became active in middle or late adulthood had a decreased risk of CHD when compared
with their long-term sedentary counterparts.
The Iowa Women’s Health Study recruited
40 417 postmenopausal women aged 55–69 from
a random sample of Iowa women drivers and
followed them for up to 7 years.15 The least active
group had about twice the cardiovascular mortality
of the most active group. Women who engaged in
moderate activities four or more times a week had a
47% lower risk than those who did so rarely or not
at all. Those participating in vigorous activities four
or more times a week had an 80% lower risk than
those who did so rarely or never.
Harvard Alumni Health Study
Since 1962, Paffenbarger and colleagues have
examined physical activity and CHD risk in a
cohort of male Harvard alumni, who have been sent
periodic surveys that request information on health
habits and medical history.
Recent evidence indicates that the accumulation
of shorter sessions of activity is associated with
equivalent benefit (in terms of CHD risk) compared
with longer sessions, provided that the total energy
expended is similar.16 Men from the original cohort
(n = 7307, mean age 66.1 years) were followed
from 1988 to 1993. They were asked to report on
walking, stair climbing, and frequency and duration of sports and recreational activities. The results
showed a progressive reduction in heart attack rates
247
with increasing total energy expenditure rather than
duration of exercise. Men accumulating the same
total energy expenditure, whether it be through one
longer episode or several shorter sessions experienced the same reduction in CHD risk. Total energy
expenditure consistently predicted a decreased risk
of CHD, whether it was through walking, stair
climbing or other recreational or sporting activities.16
The evidence of the effects of
physical activity on reducing risk
factors for CHD
In addition to providing direct protection against
CHD, physical activity provides indirect protection
through its influence on other risk factors including
high blood pressure, high cholesterol and diabetes
mellitus.
Blood pressure
Risk of CHD is directly related to both systolic and
diastolic blood pressure levels. It is estimated that
13% of deaths from CHD are due to high blood
pressure (defined by systolic BP )140 mmHg. or
diastolic BP )90).17
There is an inverse relationship between physical
activity and blood pressure. Reductions in systolic
and diastolic blood pressures of up to 11 mmHg
and 8 mmHg, respectively, can be achieved in
75% of patients with hypertension through regular
moderate physical activity.18
Randomized trials of the effects of different
intensities of exercise on blood pressure suggest
that moderate and vigorous intensity activity may
confer similar reductions in diastolic blood pressure.18 Furthermore, moderate intensity activity
causes even greater reductions in systolic blood
pressure than vigorous intensity exercise. Moderate
activity is sufficient to lower BP in normotensive
individuals, and may therefore be useful in the
primary prevention of hypertension.19
Diabetes
Diabetes substantially increases the risk of CHD, to
the extent that people with diabetes have a risk of
having a heart attack equal to that of people without
diabetes who have already had a heart attack. Men
with type 2 diabetes have a 2–4-fold greater annual
risk of CHD, with an even higher 3–5-fold risk in
women with type 2 diabetes. The prevalence of
diabetes has increased over the last 10 years by
about two-thirds in men and a quarter in women.
Around 3% of adults now have diagnosed diabetes,
248
V. Press et al.
and an estimated further 2% have undiagnosed
diabetes.17 The evidence demonstrates that physical
activity can have a significant role to play in the
prevention and management of type 2 diabetes,
particularly in people who are obese or have
impaired glucose tolerance.20–23
For example, the Nurses Health Study examined
the relationship between total physical activity and
risk of diabetes and compared the benefits of
vigorous activity and walking.24 The study looked
at 70 102 women aged 40–65 and free from diabetes, CHD and cancer. Results showed a reduction
in the relative risk of developing diabetes with
increasing total physical activity over an 8-year
follow-up period. After adjustment for covariates
such as smoking and hypertension, women in the
highest quintile of total activity had a relative risk of
0.54 (p-0.001) compared with the least active
women. This reduction in risk correlated with the
quantities of vigorous and moderate intensity
activity undertaken, including walking. Thus, the
reduction in risk is associated with total energy
expenditure.
Regular moderate physical activity (including
endurance and resistance training) is also beneficial
in the management of type 2 diabetes.25 Mild to
moderate activity is sufficient to lower blood glucose
and increase insulin sensitivity, and the effect is
sustained for up to 72 h into the post-exercise period.
Physical activity is a major under-used therapy in the
treatment of type 2 diabetes.25
A recent review paper from the American
College of Sports Medicine states that individuals
with type 2 diabetes should strive to expend a
minimum of 1000 kcal per week through physical
activity.25 Increased physical activity also appears
to be protective against heart disease in those with
type 1 diabetes.26
Overweight and obesity
Overweight and obese individuals have an increased
risk of CHD and other vascular disease. The incidence of obesity in the UK has been rising, while
the average food intake has apparently been falling.
This is probably due to an overall decrease in
physical activity levels, implying that physical activity is a crucial factor in the prevention and management of obesity.27 Currently, 63% of men and 53%
of women are either overweight or obese.17
Continued physical activity is fundamental to
achieving long-term weight loss and its subsequent
maintenance. The beneficial mechanisms behind
this relate to increases in total energy expenditure,
promotion of body fat metabolism whilst preserving
lean mass and an increase in metabolic rate.
Several studies have pointed towards those overweight but fit having lower risks than those who are
normal weight and unfit, suggesting that activity
may offset some of the health risks associated with
obesity. A recent review summarizing the epidemiological evidence suggests that the health risks of
obesity are largely controlled if a person is physically
active and physically fit.28 Unfit men have been
shown to carry a higher risk of all-cause mortality,
irrespective of waist circumference.29
Cholesterol
Risk of CHD is directly related to blood cholesterol
levels. It is estimated that 45% of deaths from CHD
in men and 47% in women are due to raised blood
cholesterol levels. The mean cholesterol level for
adults over 18 years in England is 5.5 mmol/l for
men and 5.6 mmol/l for women.17
Physical activity has favourable effects on several
aspects of the blood lipid profile. Moderate activity
appears to increase HDL levels, and a single activity
session can result in improved blood lipid profile
with effect for several days. Exercise training has
also been shown to reduce elevated levels of
triglycerides.30
The effect of physical activity on
the health of those with existing
CHD
A meta-analysis of randomized trials has shown that
cardiac rehabilitation that includes exercise reduces
mortality after myocardial infarction by at least
20%. Furthermore, exercise training in patients
with heart failure improves exercise tolerance and
quality of life in patients with NHYA class II and III
Congestive Heart Failure (CHF). Exercise is advised
not only following acute myocardial infarction but
also for left ventricular dysfunction and various
cardiac surgical procedures and interventions such
as CABG, angioplasty, cardiac transplantation,
valve replacement and patients with implanted
devices.31 Moderate intensity physical activity
reduces the risk of dying from CHD by 20% when
part of a rehabilitation programme, and is beneficial
for those with NYHA class II and III heart failure.
How active are adults in the UK?
Despite the benefits of physical activity, the
majority of people in the UK take little or no
regular physical activity. Only 37% of men and
Exercise and the heart
25% of women meet the current guidelines of
30 min moderate activity on five or more days of
the week suggested by the Government.32 Over
one-third of adults are currently sedentary, that is
undertake less than one occasion of 30 min moderate activity a week.32 Physical activity declines
rapidly with age, such that only 17% of men and
12% of women in the 65–74-year age group meet
the current guidelines.32
Risks of physical activity
There is a common fear that vigorous exertion can
trigger cardiac arrest or sudden death. Indeed, a
paradox of exercise is that physical exertion can
increase the short-term risk of sudden death, while
at the same time provide protection against this risk
in those engaging in habitual exercise.
A prospective study involving 21 481 male
participants (free of CHD) in the Physician’s
Health Study reported 122 sudden deaths over a
12-year follow-up period.33 The absolute risk of
sudden death during and up to 30 min after
vigorous exercise was extremely low (1 sudden
death per 1.51 million episodes of exertion). Those
participating in habitual as opposed to occasional
vigorous exercise were found to have a significant
reduction in the short-term risk associated with
vigorous exertion. The risk was not entirely eliminated. These data confirm that habitual vigorous
exercise diminishes the risk of sudden death during
physical exertion.
The Harvard Alumni health study showed an
increased risk of death in men who spend 3 h or
more per week participating in vigorous sport.34
The British Regional Heart study also reported an
increased risk of heart disease in men undertaking
vigorous activity, compared to those taking moderate intensity activity (relative risk = 1.68, p = 0.05).
However, the increased risk was only seen in men
with hypertension (treated or untreated).35
Contra-indications to exercise include unstable
angina, uncontrolled diabetes, uncontrolled hypertension, exercise-induced arrhythmias, severe stenotic
or regurgitant valvular disease and hypertrophic
cardiomyopathy.
Practical help for health
professionals—what works?
Interventions promoting physical activity amongst
the general public are more likely to be effective if
the suggested increase in activity can be shown to
fit into an individual’s daily routine.36 A review of
249
research has identified common features of successful physical activity interventions.37 These are: (i)
home-based programmes (not necessarily activities
based at home, but activities that could be carried
out from the home, such as walking); (ii) unsupervised informal exercise; (iii) frequent professional contact; and (iv) moderate intensity activity,
particularly walking.
Primary health care seems an obvious setting to
encourage individuals to be more physically active.
Professionals should see the promotion of physical
activity as an integral part of their responsibilities.38
The average GP’s list in the UK has around 1000
sedentary adults. Of these, 900 are free from
symptoms of CHD, 80 have angina or have had a
previous myocardial infarction, nine have heart
failure and one has had a recent myocardial
infarction.
There are many ways in which primary care
teams can promote physical activity. These are two
examples:
Walking the way to health
Walking is described as ‘the commonest and most
natural exercise and the only sustained aerobic
activity that is at all prevalent’ (Morris 1994).39
Walking is easily adopted, adhered to, and convenient for the vast majority of people. It requires no
special skills or equipment and is inherently safe.40
Walking is ideal as a gentle starting point for the
sedentary and is the main option for increasing
physical activity in sedentary populations.
Exercise referral schemes
The schemes operate by Primary Health Care
Teams referring patients who would benefit from
becoming more active, and who fit agreed criteria
for locally provided physical activity opportunities.
However, because of the large number of inactive
people, exercise referral will need to become more
of a specialist resource for primary health care and
link with community schemes.
The National Quality Assurance Framework for
Exercise Referral Schemes has recently been published.41 It contains guidelines for best practice and
best value within the whole system of referral,
extending from selection of patients to exercise
programming, evaluation and long-term follow-up.
Guidance is given on appropriate professional competencies of each person involved, including the
GP, community nurse, therapist, operational manager or exercise facility, commissioning manager
and exercise practitioner.
250
V. Press et al.
Conclusions
Regular moderate intensity physical activity gives
considerable protection against CHD. Although
vigorous intensity activity confers maximum cardiovascular benefit, this level of activity is unlikely to
be attainable or sustainable for the majority of
people.
Furthermore, the greatest gains across the population will occur if sedentary people become more
active. The numbers that could benefit by increasing physical activity are huge, since 63% of men
and 75% of women do not meet the current guidelines. A major change in attitude and behaviour is
needed to put activity back into our lives. Physical
activity not only halves the risk of CHD, but also
carries similar benefits in the prevention of stroke
and type 2 diabetes. There are reduced rates of hip
and vertebral fracture, colon cancer, as well as
beneficial effects on anxiety and depression and a
reduction in cognitive decline with age. Walking is
suggested as the most practical exercise from which
the population can achieve such improvements in
health.
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Appendix: useful resources
British Heart Foundation. Physical Activity Toolkit:
A training pack for primary health care teams.
British Heart Foundation, 2001. (Contact the British
Heart Foundation on: 020 7487 7162)
Faculty of Public Health Medicine. Handbook on
Physical Activity: Let’s Get Moving. 2001. (Contact
the Faculty of Public Health Medicine on: 020 7935
0243)
Health Development Agency. CHD Guidance
for Implementing the Preventative Aspects of the
National Service Framework, 2000. (Contact the
Health Development Agency on: 020 7222 5300)
British Association of Cardiac Rehabilitation.
Phase 4 Instruction Training Module, 2nd edn.
London, British Cardiac Society, 2001.
Walking the Way to Health: the British
Heart Foundation and the Countryside Agency.
wwww.whi.org.ukx.