Glycation is the non-enzymatic attachment of a sugar molecule to a protein, lipid, or nucleic acid — distinct from glycosylation (which is enzymatic and regulated).
Mechanism — Glucose, fructose, and reactive dicarbonyls attach to amino acid residues (mostly lysine and arginine). Early adducts are reversible (Amadori products); late adducts are AGEs. Persistent hyperglycemia accelerates the process.
Use case — Glycemic control is the lever. HbA1c is glycated hemoglobin — the diagnostic readout of cumulative glycation.
Caveats — Even normal-range glucose contributes to glycation over decades. The case for tighter than 'normal' glucose control is partly an anti-glycation argument.