Exercise and cardiovascular disease

This article reviews the effects of regular exercise on the prevention, as well as the rehabilitation, of cardiovascular disease. It also reviews the effects of exercise on cardiovascular physiology and other coronary risk factors.

Message

The article covers a great many beneficial effects of exercise, and these are just in association with cardiovascular disease. It reports that exercise helps prevent cardiovascular disease; lowers risk of death in coronary artery patients; results in many beneficial physiological changes; positively changes lipids, blood pressure, and more. The benefits of exercise are seen in men, women and older people. Although the studies are not systematically reviewed, the message is clear: it is never too late in life to start exercising, feel better and live longer!

Review

The review uses a narrative style with little or no information on the contributing papers: how they were identified, the study designs, participant numbers or statistical analyses.

Reference

T Miller et al. Exercise and its role in the prevention and rehabilitation of cardiovascular disease. Annals of Behavioral Medicine 1997 3: 220-229.

Results

Exercise and prevention of cardiovascular disease

Three reviews of 50 observational studies found the risk of cardiovascular disease was lower in physically active individuals. A review of 43 epidemiological studies found that physical inactivity was associated with double the risk of developing cardiovascular disease.

Exercise rehabilitation of cardiovascular disease

Two meta-analyses examined 22 randomised controlled trials with 4,000 patients over three years. They reported a 20% to 25% reduction in both all-cause and cardiovascular mortality among patients receiving rehabilitation after myocardial infarction compared with those not receiving rehabilitation.

Effects of exercise on physiology

Typically, studies used a program of aerobic exercise (eg. walking, cycling) performed at an intensity of 50% to 80% maximum heart rate for 30 minute sessions, three to five days a week for four to twenty weeks.


In both healthy individuals and coronary artery disease patients, exercise resulted in an increase in:

maximum oxygen uptake (VO2 max is the aerobic capacity or maximum oxygen uptake and is a measurement which determines how much exercise you can tolerate. A fit person consumes a high volume of oxygen per heartbeat during exercise);

higher stroke volume s at both rest and during exercise (the amount of blood pumped out of the heart from a single contraction);

lower resting heart rate ; and

beneficial changes in skeletal muscle allowing for more efficient supply and use of oxygen (These changes include increased capillary density, myoglobin content and oxidative enzyme capacity).


E xercise has been found to reduce age-related changes in cardiovascular function. Maximum oxygen uptake decreases with age, but less so in physically active individuals. Left ventricular function (known to decline with age) also improves with exercise. Five studies found that regular exercise was associated with a reduction in risk of death between 25% and 50% in older adults (aged 60 or more, 70 or more and aged 75 years or more).

In patients with coronary artery disease, eight out of twelve randomised controlled trials reported improvement in symptoms of angina and heart failure. Several studies showed a reduction in the severity of exercise-induced ischaemia (claudication, acondition in which pain occurs in the legs with exercise as a result of reduced bloodflow to the leg muscles. The cause is hardening of the arteries).

Effects of exercise on coronary risk factors

Smoking. There is no evidence that exercise enhances smoking cessation.

Lipids . In a meta-analysis of 95 studies exercise was associated with average reductions in total cholesterol of 7 to 13 mg/dL, low-density lipoprotein cholesterol 3 to 11 mg/dL and triglycerides 14 to 22 mg/dL. The larger changes were seen in subjects who also lost weight. The increase in high-density lipoprotein cholesterol was only 2 mg/dL, regardless of weight loss.

Hypertension . Two reviews of 34 studies reported an average reduction of 6 to 9 mmHg for systolic and diastolic blood pressure in patients with mild to moderate hypertension.

However, the authors report design flaws in these studies. Some of the lipid studies used healthy adults with low lipid values at the start of the study and low intensity exercise programs for short periods of time. Many of the hypertension studies had small numbers of participants.

Non-insulin-dependent diabetes mellitus . Three epidemiological studies suggest that exercise prevents the development of non-insulin dependent diabetes mellitus.

Psychological wellbeing. The independent contribution of exercise on psychological wellbeing is often difficult to determine. This is because (i) many studies have examined the combined effects of exercise with counselling and (ii) many have examined more than one aspect of psychological wellbeing and seen improvements in some aspects, but not in others. However, several studies suggest that exercise reduces the occurrence of depression in healthy individuals and reduces the severity of depression in cardiac rehabilitation patients.

Comment

The reduction in death seen in rehabilitation patients may be attributable to other lifestyle changes (eg. improved diet) as well as exercise. Although exercise does not enhance smoking cessation, it can help to reduce the weight gain often seen with smoking cessation. Greater physiological changes could be observed in studies addressing the design flaws of those reviewed here. However, it is difficult to measure the direct impact of exercise on risk factors and in this case, exercise may result in weight loss which by itself impacts blood pressure and lipid measurements.

The upside of this review is that it covered an enormous amount of material relating exercise to cardiovascular disease. The downside is that it was impossible to systematically review every area and therefore impossible to judge the quality of the papers and their results. The results should be considered with circumspection (although the authors appear to provide a balanced account of the literature and their review provides an excellent starting point for gathering further evidence).

Perhaps most importantly, the overriding message is that exercise can be beneficial in so many ways - even if you are just beginning to exercise and over 60 years of age.