Coronary heart disease contributes much to the burden of morbidity and mortality from chronic diseases in industrialized countries. Three major risk factors--high serum cholesterol, smoking, and high blood pressure--are known to affect adversely coronary heart disease. Many countries have accordingly adopted prevention policies designed to reduce the prevalence of these three risk factors and, in turn, alleviate the burden of coronary heart disease in their populations. Like these three risk factors, physical inactivity is associated with about a twofold increased risk of developing coronary heart disease (1). Since physical inactivity is also highly prevalent in virtually all industrialized countries, it should have a place in this list of important modifiable risk factors.
Physical inactivity: a risk factor for coronary heart disease
In most observational studies an association between physical inactivity and an increased risk of coronary heart disease has been identified (1). No randomized controlled trials have focused, however, on the effect of eliminating physical inactivity on coronary heart disease in general populations. Policy-makers considering the significance of physical inactivity in coronary heart disease therefore have to rely on expert assessment of the available data. Experts have essentially accomplished this by applying the same criteria previously used to assess the harmful effects of smoking on lung cancer.
In this way it has been concluded that a harmful, positive association exists between physical inactivity and the incidence of coronary heart disease (1). This association has the following characteristics:
-- it is consistently observed in a variety of settings
(and especially in most of the better-designed
-- it is strong (i.e., the most inactive people have an
almost twofold greater risk than the most active
people, and the magnitude of the association is
similar to that for the other three important risk
factors for coronary heart disease);
-- it is appropriately sequenced (i.e., assessment of
the physical activity level predates the onset of
coronary heart disease);
-- it is biologically graded (i.e., the risk increases
with decreasing physical activity); and
-- it is plausible and coherent, as reflected by exist-
ing scientific knowledge.
Physical inactivity may result in coronary heart disease through various physiological mechanisms, which relate partly to detrimental effects on blood pressure, serum lipoprotein profiles, as well as insulin and glucose metabolism (2). Each of these effects may have a subsequent influence on atherosclerotic processes. Most studies that have statistically adjusted for the confounding effects of the traditional risk factors indicate that physical inactivity is also an independent risk factor for coronary heart disease (1). Because this finding has not been demonstrated in all studies, however, the issue is still the subject of some discussion. Regardless of the precise nature of the mechanism, physical inactivity is, nevertheless, an important risk factor for coronary heart disease.
Impact of physical inactivity on public health
Technological progress in industrialized countries has generally led to decreasing physical activity in most jobs (3). Therefore, public health attention often focuses on eliminating leisure-time physical inactivity, which is highly prevalent compared with the prevalence of the traditional risk factors for coronary heart diseases (4). In the USA, for example, an estimated 56% of men and 62% of women fail to engage in regular leisure-time physical activity (i.e., at least three times per week for 20 minutes per session), and 25% of men and 30% of women perform no leisure-time physical activity (5). …