Glycation (non-enzymatic glycosylation) is the covalent attachment of a sugar to a protein, lipid or nucleic acid molecule. Typical sugars that participate in glycation are glucose, fructose, galactose, and their derivatives. Glycation is the non-enzymatic process responsible for many (e.g. micro and macrovascular) complications in diabetes mellitus and is implicated in other diseases and in aging.
In contrast with glycation, glycosylation is the enzyme-mediated ATP-dependent attachment of sugars to a protein or lipid.]]
thumb|right|266px|[[Imidazolones (R = CH<sub>2</sub>CH(OH)CH(OH)CH<sub>2</sub>OH) are typical glycation products. They arise by the condensation of 3-deoxyglucosone with the guanidine group of an arginine residue.]]
Glycations occur mainly in the bloodstream to a small proportion of absorbed simple sugars. Fructose has approximately ten times the glycation activity of glucose, the primary body fuel. Glycation can occur through Amadori reactions, Schiff base reactions, and Maillard reactions; which lead to advanced glycation end products (AGEs).
Long-lived cells (such as nerves and brain cells), long-lasting proteins (such as crystallins of the lens and cornea), and DNA can sustain substantial glycation over time. Damage by glycation results in stiffening of the collagen in blood vessel walls, increasing blood pressure, especially in diabetes. Glycations also cause weakening of the collagen in blood vessel walls, which may lead to micro- or macro-aneurysm; or strokes if in the brain.
A 2025 study reported that a combination of nicotinamide (a form of vitamin B3), ⍺-lipoic acid (ALA), thiamine (vitamin B1), pyridoxamine (a form of vitamin B6), and piperine reduced glycation damage in cell and mice models accompanied by non-muscle weight loss, apparently due to reduced Ghrelin and AMPK production.
DNA glycation
The term DNA glycation applies to DNA damage induced by reactive carbonyls (principally methylglyoxal and glyoxal) that are present in cells as by-products of sugar metabolism. DNA glycation can cause mutation, breaks in DNA and cytotoxicity.