UKPDS: Glycemic Control—Effects on Microvascular Endpoints

• With respect to microvascular complications, epidemiologic analysis revealed that a continuous and significant relation exists between the hazard ratio of microvascular endpoints and glycemia over time as represented by an updated mean of annual measurements of HbA1c for every percentage point decrease in HbA1c (eg, 9% to 8%), the risk of complications was reduced by 37%
  there is no evidence of a threshold for microvascular complications above normal HbA1c level. An HbA1c level of <6% is the reference category with a hazard ratio of 1 the quantitative relationship shown here for type 2 diabetes and microvascular complications is similar to those shown for type 1 diabetes in the DCCT.

 Stratton IM et al. BMJ. 2000;321:405-412.