Impact of Interventions

This page gives detail on the assumptions used in the Risk Calculator on the impact of each intervention available. For greater detail, read the JBS3 Report, as taken from the JBS3 report.

The impact of risk factor reduction, both alone and in combination, on key measures can be estimated. The impact of traditional risk factors such as BP, smoking, and cholesterol on lifetime CVD outcome is strongly reinforced. Even a single major risk factor from early life is linked with substantially increased lifetime risk for CVD. It is clear that even a relatively low risk factor burden over a long period has an important impact on future CVD outcomes. The lifetime benefits of even small reductions in risk factors, when introduced at an early age, can be seen by using the JBS3 Risk Calculator.

Direct evidence of the effect of changing behaviour or intervening to change physiological measures comes from clinical trials; it is also possible to make indirect inferences from observing cohort studies. However, evidence is limited and some assumptions are inevitable.

Blood pressure: In a recent review of trial data,[36] Law et al estimated an approximate 50% reduction in CVD events per 20 mmHg reduction in SBP, which is similar to that expected from the epidemiological evidence for CVD mortality from the Prospective Studies Collaboration.[37] This is substantially larger than the association found in the QRISK® Lifetime-risk formula, which uses a hazard ratio of 1.13 (female) and 1.11 (male) per 20 mmHg increase in systolic BP, i.e., around 11% reduction in event rate per 20 mmHg reduction in systolic BP. This is a substantial difference that is likely to be due to the many other correlated factors included in the risk formula. In JBS3, the Law et al estimate has been adopted, which corresponds to a hazard ratio of 0.966 per mmHg reduction in SBP. Law et al reported no impact of blood-pressure intervention on non-CVD causes of death.

Cholesterol : A recent meta-analysis estimated a 22% reduction in CVD event rate per 1 mmol/L reduction in LDL-c over a wide range of baseline conditions.[11] Since total cholesterol (TC) and HDL-c are readily measured in general practice, JBS3 has adopted non-HDL = TC – HDL-c as the measure of intervention: assuming that non-HDL is approximately 1.24 x LDL[38] this leads to a hazard ratio of (0.78)1/1.24 = 0.82 per 1 mmol/L reduction in non-HDL-c. No impact of cholesterol interventions on non-CVD causes of death has been assumed.

Smoking: Since ‘former smoker’ is a category in the QRISK lifetime score, it has been assumed that an intervention to stop smoking leads to the epidemiological risk associated with ‘former smoker’. There is also a clear impact on non-CVD causes of death, and again the ‘former smoker’ risk is assumed.

Weight: No reliable data on the effect of weight reduction in its own right is available, rather than through its effect on BP and cholesterol, and so currently weight has not been included as an intervention. Whilst weight and height are included in the risk calculator, a weight reduction entered into the risk calculator will not in itself lead to any change in CVD risk score, as associated risk factors changes in blood pressure and lipids are not automatically modelled. However, it is known that a 10% weight loss will typically lead to a 10 mmHg reduction in systolic BP, a 10% reduction in TC and an 8% rise in HDL-c. Such changes, or those expected for a given weight reduction should be entered directly to help determine expected risk changes with weight loss.