Hyperglycaemia: link to excess mortality.

Asymptomatic diabetes is defined by chronic hyperglycaemia. The 2-h post-challenge glucose level is not generally used in practice and consequently not recommended for diagnosis, so diabetes is defined from fasting hyperglycaemia. Several large studies have been used to evaluate the impact of different diagnostic definitions on the risk of premature death. Meta-analysis of component studies in the Diabetes Epidemiology: Collaborative Analysis of Diagnostic Criteria in Europe (DECODE) study showed that for all-cause mortality fasting glucose did not carry an independent risk but the 2-h post-challenge glucose carried a significant risk after adjusting for factors including fasting glucose. Increasing fasting glucose also did not carry a significant excess risk for cardiovascular mortality but there was an overall significant relative risk with increasing 2-h post-challenge glucose. Analysis of 20-year follow-up data from the combined Whitehall, Paris and Helsinki studies demonstrated that after adjusting for other risk factors men in the upper 20 per cent of the 2-h glucose distribution and those in the upper 2.5 per cent for fasting glucose had a significantly higher risk of all-cause mortality compared with men in the lower 80 per cent of each distribution. Analysis of the Paris Prospective study alone showed that all-cause mortality was highest in those with isolated 2-h post-challenge hyperglycaemia. In men without known diabetes there were J-shaped relationships between both fasting and 2-h glucose and all-cause, cardiovascular and cancer mortalities. Fasting and 2-h glucose levels are highly correlated and hyperglycaemia by either definition is undoubtedly a risk factor for premature death, whatever the cause.