Exercise in the prevention of Coronary Heart Disease (CHD):
The UK experience
Back in the 1950s and 1960s, Professor Morris’ studies of bus drivers and Whitehall civil servants were epidemiological classics. In the former he and his colleagues compared the heart disease rates in London bus drivers with those of bus conductors. The comparison was between the drivers sitting all day long fuming at the pesky taxi drivers and other road users versus the conductors who shinned up and down stairs getting plenty of exercise. They found that the drivers had a more than 40% higher rate of CHD than the conductors.
The Whitehall civil servant study looked at leisure time physical activity. Again they found that those who took vigorous exercise as recreation had about 40% of the fatal heart attack rate of the inactive and 50% the non-fatal attack rate.
Morris made several discoveries: that intermittent heavy exercise is more effective than lower level activity, even with equivalent totals of exercise; that there is a threshold for the protective effect; and there is dose response relationship above this level ie the more exercise you take the better the effect.
The US experience
In the USA, Paffenbarger and his colleagues performed similar studies on the San Francisco long-shore men (stevedores) and on university graduates. In a study of nearly 17,000 Harvard graduates aged 35–74, they found that taking exercise was inversely related to mortality. In other words the more they exercised the less they were likely to die in the period of observation. A further study from the US followed over 26,000 men and women who had performed an exercise test to determine their levels of physical fitness. They divided the subjects by fitness level – high, moderate and low. Over an average follow up of 10 years the rate of coronary disease was 25% lower in the high fitness group when compared to the low fitness group.
The World experience
Since then numerous studies from all over have confirmed the association between regular exercise, physical fitness and protection from CHD. They have shown that total physical activity such as running, weight training, and rowing are each inversely associated with risk of developing or dying from CHD. Improving fitness level from unfit to fit nearly halves risk compared with those who remain unfit. Most tellingly has been a meta-analysis of 33 trials which included over 100,000 subjects. They were followed up for an average of 11 years after an exercise test which divided them into low, intermediate and high fitness categories. The low fitness group had a 56% higher chance of suffering a heart attack than the high fitness group. The beneficial effects of exercise holds for all age groups for whom the figures have been sought.
How does exercise work?
Some of the ways in which exercise prevents CHD are obvious – by reducing most of the reversible risk factors. Regular exercisers are thinner than non-exercisers, have lower blood pressure, lower blood cholesterol and are less likely to develop diabetes.
Apart from stopping smoking, if you do, there is no more effective way of avoiding a heart attack than regular vigorous exercise.
Next week I will discuss the use of exercise to reduce the effects of CHD once it has developed.