Diabetes is associated with an increased risk of major coronary events and all cause mortality, however, only early-onset disease appears to confer CHD equivalence, a study in Archives of Internal Medicine concludes.

The authors used data from the British Regional Heart Study, a prospective study of cardiovascular disease in men from 24 British towns who underwent screening from 1978 to 1980. The 4,045 men aged 60 to 79 years participating in the study were classified as having: no prior diabetes or MI; late-onset diabetes (diagnosed >60 years of age) or undiagnosed diabetes; early-onset diabetes (diagnosed

The results showed that both early- and late-onset diabetes were associated with an increased risk of major CHD events, hazard ratio 2.39 (95% CI: 1.41-4.05) and 1.54 (95% CI: 1.07-2.21) respectively; cardiovascular disease 2.08 (95% CI: 1.33-3.25) and 1.37 (95% CI: 1.01-1.84) respectively and all cause mortality 1.68 (95% CI: 1.19-2.38) and 1.31 (95% CI: 1.06-1.62) respectively, compared with individuals without diabetes.

This held true even after adjustment for other risk factors such as age, smoking, alcohol consumption, social factors, body mass index, physical activity, blood pressure, HDL and total cholesterol, and risk markers.

However, as can be seen from the quoted hazard ratios the risk was significantly higher among individuals who developed diabetes before 60 years of age than among those who developed it later. More importantly patients who developed early-onset diabetes (associated with a disease duration of 16.7 years) had a risk of major CHD events and cardiovascular disease similar to men with a prior history of MI, 2.51 (95% CI: 1.88-3.36) and 2.17 (95% CI: 1.71-2.7) respectively.

Many clinicians regard the presence of diabetes mellitus as a coronary risk equivalent and would favour a secondary prevention approach with such patients even in the absence of established cardiovascular disease. Others would debate this and treat diabetes patients according to established primary prevention risk scoring systems applying the standard risk thresholds for intervention.

The authors conclude from a further analysis of the duration of diabetes that CHD risk in patients with diabetes escalates significantly with time and approaches CHD risk equivalence only when the disease has been present for more than eight years. The reasons for this could be that those patients developing diabetes later in life might be less insulin resistant and have had less exposure to chronic hyperglycaemia.

From a practice perspective perhaps we should manage those with a longer history of diabetes as a coronary risk equivalent and those with more recent onset diabetes according to global cardiovascular risk.

Dr Peter Savill