Does non-diabetic hyperglycemia predict future IHD? Evidence from the Caerphilly and Speedwell studies

We have examined the risk of subsequent ischemic heart disease (IHD) in men according to their initial fasting plasma glucose level in a prospective cohort study (Caerphilly Collaborative Study) of 4860 middle aged men from South Wales and Bristol, U.K. Ninety-four men reported themselves to be diabetic at initial screening and fasting venous plasma glucose levels were determined in these men and in a further 4519 non-diabetic men. At follow-up new IHD events occurred twice as commonly in diabetics compared to non-diabetics and overall mortality was increased 4-fold. Among non-diabetics however, increased IHD events only occurred in men with fasting values at the upper end of the distribution of baseline plasma glucose values [at 6.8 mmol/l (122 mg/dl) or more]. This association was reduced, but remained statistically significant, after adjusting for factors associated with plasma glucose levels; body mass index, plasma triglyceride, smoking habit and pre-existing IHD. In conclusion there is no evidence of a consistent, graded increase in risk of IHD by initial fasting plasma glucose level although the risk is significantly increased in men with baseline plasma values at 6.8 mmol/l (122 mg/dl) or more, and also in diabetics. This study suggests that such levels probably represent a pre-diabetic state in many individuals. Appropriate non-pharmacological intervention may be useful in halting the progression to the diabetic state, although this should be tested in experimental studies.