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.

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 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 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

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 
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 

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, 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 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 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.

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.

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. [www.whi.org.uk].

Address correspondence to Professor Sir C.F. George, British Heart Foundation, 14 Fitzhardinge Street, London W1H 6DH

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