Hgb A1c is a marker. Of steady state blood glucose, and is formed spontaneously by nucleophilic attack of the b-globin n-terminal amino group on the anomeric carbon (aldehyde carbon) of glucose. Following a chemical rearrangement (an amadori rearrangement), the modification on hemoglobin is "locked in". The best way to lower is to control your blood sugar consistently through time. It will fall as rbcs turnover.