Glycemic exposure over time for each individual was determined from the updated mean of measurements of A1c made each year during follow-up. For each 1% decline in updated A1c, the reduction in risk for microvascular complications and amputation or death from peripheral vascular disease was the greatest. Risk for microvascular disease declined by 37% (95% CI, 33% to 41%; P<0.0001), and risk for amputation or death from peripheral vascular disease decreased by 43% (95% CI, 31% to 53%; P<0.0001).
In comparison, risk for MI declined by 14% (95% CI, 8% to 21%; P<0.0001); risk for stroke decreased by 12% (95% CI, 1% to 21%; P=0.035); and risk for heart failure decreased by 16% (95% CI, 3% to 26%; P=0.016). In addition, risk for cataract extraction decreased by 19% (95% CI, 11% to 26%; P<0.0001) for each 1% reduction in updated A1c. Notably, there was no indication of an updated A1c threshold for any complication below which risk no longer decreased or a level above which risk no longer increased.
This prospective observational study demonstrates that risk for diabetic complications is strongly associated with previous hyperglycemia. Moreover, the results show that any reduction in A1c is likely to reduce the risk for both microvascular and macrovascular complications. The lowest risk is associated with A1c values in the normal range (<6%).

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