Glycerol is one of the most common alcohols found in human metabolism. It is a 3-carbon molecule containing three hydroxyl groups. Its molecular formula is C3H8O3, and its molecular weight is 92.09 daltons. A syrupy liquid with a sweet taste, glycerol is about 0.6 times as sweet as cane sugar. Glycerol is also known as glycerin, glycerine, 1,2,3-propanetriol and trihydroxypropane.
Glycerol is the backbone of triacylglycerols (triglycerides or neutral fats) and phospholipids. These substances are present in most life forms, and dietary intake of glycerol comes mainly from these molecules in animal and plant products. Glycerol is also used as a sweetner in syrup, liquor and some foods.
Glycerol has had diverse uses in medicine. It has moisturizing and lubricating properties and can increase serum osmolality. It is given orally to reduce intraocular pressure and vitreous volume in eye surgery and is used as an adjunct in the management of acute glaucoma. Glycerol may also be used topically to reduce corneal edema, which may be of use in eye examinations. Glycerol has also been used (intravenously or orally) for the management of cerebral edema secondary to acute stroke, to lower intracranial pressure and to improve rehydration during acute gastrointestinal disease. It is a hyperosmotic laxative and may be used rectally in suppositories. It is used as a cerumenolytic and as a demulcent in cough preparations.
Oral glycerol by itself may have dehydrating activity. However, if ingested with added fluid, it may increase total body water. This is known as glycerol hyperhydration, and glycerol is used by some athletes to improve thermoregulation and endurance during exercise or exposure to hot environments.
The main effect of glycerol itself results from its dehydrating activity. For example, oral glycerol can increase serum osmalility, thus drawing fluid from other parts of the body. This is the mechanism, at least in part, for its ocular hypotensive effect in the treatment of acute glaucoma. Therefore, it seems paradoxical to talk about glycerol's hyperhydration effect. However, in combination with ample water, it may be more hydrating than water alone, at least for some. The mechanism of this effect and how it may relate to enhanced athletic performance is still highly unclear.