SIGN 97: Risk estimation and the prevention of cardiovascular disease

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5 Physical activity

Physical activity has been defined as any bodily movement that results in energy expenditure.89 Physical activity can be categorised as occupational (physical activity at work), leisure time (non-occupational physical activity), exercise (physical activity that is structured and done for a specific reason) and active living (eg non-recreational walking, housework and gardening). Physical activity is commonly described as having three dimensions: duration (eg minutes, hours), frequency (eg times per week or month) and intensity (eg rate of energy expenditure).90

Regular activity has both preventive and therapeutic effects on many chronic conditions such as CHD, stroke, cancer, musculoskeletal disorders, obesity, diabetes and mental illness.91 Evidence level 4

5.1 Physical activity and cardiovascular risk

5.1.1 Physical activity as an independent risk factor

Ten observational studies that examined the effects of physical activity on CVD, after controlling forotherkeyriskfactors,wereidentified.Allstudies(orspecificelementsofthestudies)confirmed an inverse relationship between physical activity and the risk of a coronary event.19, 92-100

Effect sizes ranged from non-significant relationships for specific types of activity (eg active commuting; hazard ratio=1.08, 95% CI 0.95 to 1.23)93 to highly significant associations (eg men who ran for an hour or more per week had a 42% risk reduction, RR 0.58, 95% CI 0.44 to 0.77) compared with men who did not run (p<.001).100 One well conducted case control study reported a multivariate odds ratio of 0.51 (95% CI 0.29 to 0.90) when comparing low levels of occupational physical activity against higher levels.92 Similar results were reported for leisure time activity. This suggests that physical activity can reduce the risk of a coronary event, when all other major risk factors are controlled for, by as much as a half. Evidence level 2++

5.1.2 Levels of physical activity

The types of activity, durations, frequencies and intensities utilised in the ten studies varied greatly. This lack of consistency makes it difficult to draw detailed conclusions in relation to the exact type, quantity and quality of activity required for a benefit.

The evidence indicates that activities of moderate intensity are protective. For example, INTERHEART, one of the largest case control studies of its kind, reported an odds ratio of 0.86 (95% CI 0.76 to 0.97) for reduction in incidence of myocardial infarction for activities that included walking, cycling or gardening.19 In another study that compared distance walked per day, those who walked less than 0.25 miles per day had double the risk of CHD mortality or morbidity of those who walked more than 1.5 miles per day (RR 2.3, 95% CI,1.3 to 4.1) which represented an increase in absolute risk of 2.6%.94 Evidence level 2++

The evidence also suggests a dose response relationship for both intensity and duration. For example, a study of postmenopausal women showed that women in increasing quintiles of energy expenditure measured in metabolic equivalents (METS) had adjusted relative risks of coronary events of 1.00, 0.89, 0.81, 0.78 and 0.72 respectively (p for trend <0.001).96 Similar trends exist for duration of exercise.95 Evidence level 2+

The type of activity appears to be relatively unimportant. For example, one good quality study reported comparable effects for both occupational and leisure time activity.92 Evidence level 2++

Activity may not need to be continuous to be of benefit. One study reported that after accounting for total energy expended on physical activity and potential confounders, duration of activity did not have an independent effect on CHD risk (p trend=0.25); that is, longer sessions of exercise did not have a different effect on risk compared with shorter sessions, as long as the total energy expended was similar.97 Evidence level 2+

Although no major adverse events were reported in the studies reviewed and it is generally accepted that the benefits of activity greatly outweigh the risks,91 there is some evidence of increased risk with activity, particularly in those who are currently sedentary. It has been suggested that those with low levels of habitual vigorous activity are twice as likely to suffer sudden cardiac death during or after exercise compared to those with high levels of habitual activity.101 Evidence level 2+, 4

BPhysical activity of at least moderate intensity (eg makes person slightly out of breath) is recommended for the whole population (unless contraindicated by condition).

BPhysical activity should include occupational and/or leisure time activity and incorporate accumulated bouts of moderate intensity activities such as brisk walking.

BThose who are moderately active and are able to increase their activity should be encouraged to do so. Activity can be increased through a combination of changes to intensity, duration or frequency.

[Good practice point] All patients, irrespective of health, fitness or activity level, should be encouraged to increase activity levels gradually.

The evidence reviewed and corresponding recommendations are in general agreement with nationally recognised recommendations that state all adults should accumulate 30 minutes, and children 60 minutes, of moderate intensity activity on most days of the week.102 Evidence level 4

National guidance is available on the most effective way to promote physical activity.46,103

5.1.3 Effects of physical activity on other key risk factors

Several meta-analyses provide evidence for a significant effect of exercise on CHD risk factors. One meta-analysis combined results of 28 RCTs of mainly healthy white adults.104 Diets which reduce saturated fats aiming to lower LDL cholesterol levels also tend to reduce the level of protective HDL cholesterol; however, exercise can attenuate this effect. Despite a large degree of variability, endurance exercise training had a favourable influence overall on the blood lipid profile relative to future risk of CHD. The most commonly observed lipid change in all weight categories in relation to endurance training was a significant (p<0.05) increase in HDL cholesterol. Reductions in LDL cholesterol (-5.0%, p<0.05), triglycerides (-3.7%, p<0.05%), and total cholesterol (-1%, not significant) were observed less frequently (independent of dietary interventions). There was a marked inconsistency in response of blood lipids. Twenty-four of 51 studies showed an increase in HDL cholesterol but the range over all studies was from -5.8% to +25%. It was not possible to establish a dose-response relationship between duration, intensity or frequency of exercise and blood lipid response. Evidence level 1+

A further meta-analysis of 54 trials showed that previously sedentary adults could decrease systolic blood pressure by 3.8 mm Hg (95% CI 2.7 to 5.0 mm Hg, p <0.001) and diastolic blood pressure by 2.6 mm Hg (95% CI 1.8 to 3.4 mm Hg, p < 0.001) with regular aerobic exercise.105 Exercise lowered blood pressure in people who were normotensive or hypertensive; overweight or of normal weight; and black, white, or Asian. The blood pressure reductions tended to be less marked in trials with longer follow up periods, most likely because adherence to the intervention programme decreased over time. All forms of exercise studied appeared to be effective in reducing blood pressure, and again, there was no relation between the frequency or intensity of the exercise and the clinical result. Evidence level 1+

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