and continuing activity protects against heart
disease; men who were active in their youth but
became sedentary in middle-age experience a
risk similar to that of men who had never been
active. Second, men who improved either their
physical activity level or their fitness level
between one observation period and another
some years later experienced a lower risk of
death than men who remain sedentary. To put
these levels of risk reduction into perspective,
taking up physical activity was as effective as
stopping smoking.
The role of exercise intensity in determining
CHD risk is still uncertain. Several key studies
have shown substantial reductions in risk with
accumulation of physical activity, most of which
was at a moderate intensity (see Haskell 1994).
However, other evidence argues that more vigor-
ous physical activity may provide unique bene-
fits. These uncertainties should not, however,
detract from the wealth of evidence, gathered
over a long period and in different populations,
that identifies physical inactivity as a major risk
factor for CHD.
Mechanisms by which exercise might confer a
lower risk of CHD include effects on blood pres-
sure, weight regulation, lipoprotein metabolism
and insulin sensitivity—all of which are dis-
cussed below. Another suggestion, arising from
the evidence referred to above that only current
exercise protects against CHD, involves an effect
on the acute phase of the disease—the throm-
botic component, for example. This possibility
is supported by associations between exercise
habits and haemostatic factors and is an area jus-
tifying more research.
Stroke
Atherosclerotic damage to cerebral arteries is a
prominent feature of stroke, so an effect of ha-
bitual exercise on the risk of having a stroke is
plausible, but there is little direct evidence. In the
British Regional Heart Study (Wannamethee &
Shaper 1992), the age-adjusted rate for strokes
showed a steep and significant inverse gradient
with physical activity category in men with or
42 nutrition and exercise
without heart disease or stroke at baseline; the
risk in moderately active subjects was less than
half that reported for inactive men. Data from the
Honolulu Heart Program (Abbott et al. 1994)
show an association between the risk of stroke
and a physical activity index in older middle-
aged men (55–68 years) but not in younger men
(45–54 years); the excess incidence of haemor-
rhagic stroke in inactive/partially active men
was three- to fourfold. For thromboembolic
stroke, among non-smokers the risk for inactive
men was nearly double that for active men but
there was no effect in smokers.Hypertension
About 16% of men and 14% of women in
England have hypertension (systolic blood pres-
sure >159 mmHg and/or diastolic >94 mmHg).
It is a major public health problem; even mild to
moderate elevations in blood pressure substan-
tially increase the risk of developing CHD,
stroke, congestive heart failure and intermittent
claudication in both men and women.
There is some evidence that high levels of
physical activity decrease the risk of developing
hypertension (see Paffenbarger et al. 1991). For
example, of 5500 male Harvard alumni free of
hypertension at entry to the study, 14% devel-
oped the disease during 14 years’ observation.
Contemporary vigorous exercise alone was asso-
ciated with lower incidence, chiefly among men
who were overweight-for-height. Similar conclu-
sions arise from study of fitness levels in relation
to risk of hypertension: during follow-up of 6000
men and women over 1–12 years (median, 4) the
risk of developing hypertension was 1.5 times
greater for those with low fitness (the bottom
75% of the sample) than for those deemed to
have high fitness (the top 25%).
The rationale for a role for exercise in the pre-
vention of hypertension is that, during exercise,
there is marked dilation of blood vessels in active
skeletal muscle, decreasing resistance to flow.
This persists during the recovery period, possi-
bly contributing to the chronic lowering of (arte-
rial) blood pressure which is often associated