Glycerol as an ingredient in food
The use of glycerol in beverages for athletes to enhance and maintain hydration status and to improve endurance exercise performance is described . Glycerol when used as a component of a hyperhydration strategy is prohibited by the World Anti‐Doping Agency (WADA) .
Pharmaceutical use
Glycerol is used in pharmaceutical products as an active ingredient as well as an excipient, e.g. solvent, plasticiser or lubricant . When glycerol is used as an excipient in medicinal products for oral administration and the glycerol intake is equal or above 10 g per single dose of the medicinal product, the information ‘May cause headache, stomach upset and diarrhea’ is required for the package leaflet . As an active ingredient, glycerol is used as an osmotic dehydrating agent. It is given orally, e.g. for the reduction in intra‐ocular pressure before and after ophthalmic surgery and as an adjunct in the management of acute glaucoma or to reduce intracranial pressure .
Glycerol has been used therapeutically by intravenously or oral administration to mobilize edema and to induce osmotic diuresis. Clinical experience and data from clinical studies are found in the literature indicating that doses up to 60,000 mg intravenously, infused over 1–4 hour, for a treatment duration of 1 week and in some studies, several weeks, and bolus oral doses (initial dose 1,500 mg/kg body weight, followed by 500–700 mg/kg body weight every 3 hour) or 500–1,000 mg/kg body weight .
The European Food Safety Authority (EFSA) Panel considered that the therapeutic administration of glycerol by oral administration to patients reported to be suffering disease that could impact significantly on their physiological functionality was not relevant in the safety assessment of glycerol as a food additive. However, glycerol has been prescribed for reduction in intraocular pressure in patients with glaucoma and may be prescribed prior to intraocular surgery . For this indication, glycerol was reported to be administered orally as a bolus dose of 1,000–1,500 mg/kg body weight (as a 50% solution) with a daily total oral dose not higher than 120,000 mg (about 1,700 mg/kg body weight) . The European Food Safety Authority (EFSA) Panel considered that the therapeutic administration of glycerol by oral administration to patients reported to be suffering ocular disease – such as glaucoma and administration of glycerol to control participants in clinical studies – were relevant for the safety assessment of glycerol as a food additive.
The European Food Safety Authority (EFSA) Panel noted that for oral therapies to patients with ocular disease or healthy controls, glycerol was administered as a bolus at 1,350 mg/kg body weight ; 1,500 mg/kg body weight ; 1,500 mg/kg body weight; 1,000 mg/kg body weight ; 1,000–1,270 mg/kg bw (McCurdy et al., 1966); 1,350 mg/kg body weight ; 1,200 mg/kg body weight and 1,260 mg/kg body weight . The only side effects observed in these oral therapies to patients with ocular disease or healthy controls were either none or one or more of nausea, headache and/or vomiting.
Guidelines for glycerol use in hyperhydration and rehydration associated with exercise report 28 studies in which oral doses between 500 mg/kg body weight and 1,500 mg/kg body weight were given in the total of 238 subjects . Three studies reported side effects after rapidly administering the glycerol as a concentrated bolus followed by fluid ingestion. Four subjects in two of the trials were nauseous after glycerol ingestion. In another study, two subjects developed diarrhea in the 24 hours after the trial. In a further three studies, a low incidence of gastrointestinal distress (bloatedness) or light‐headedness were reported.
Using the studies of Wald and McLaurin , the European Food Safety Authority (EFSA) Panel noted that patients were administered glycerol orally as bolus doses of 500–1,000 mg/kg body weight every 3–4 hour, dependent on the patients’ intracranial pressures (ICPs). Specific individual dosages ranged from 4,000 mg to 70,000 mg (average 54,000 mg) and it was administered via a nasogastric tube as a 50% solution (by mixing a 100% glycerol solution with an equal volume of either 5% dextrose in water or 5% dextrose in 0.4% normal saline, depending upon the systemic electrolyte status). If no change in intracranial pressure was achieved or a significant volume of solution was aspirated from the stomach, intravenous mannitol was administered and another trial of the drug was initiated 4–24 hour later. For the six patients in which data were reported in this study, maximum intracranial pressure reduction and maximum serum glycerol concentration occurred around 60–90 min after oral bolus ingestion. In most cases, the serum glycerol concentration returned to pre‐treatment levels around 3 hour after oral administration.
Given the dose‐ and time period‐range reported in this study, the European Food Safety Authority (EFSA) Panel calculated that the dose of glycerol required to induce a therapeutic reduction in intracranial pressure (ICP) was within the range of 125–333 mg/kg body weight per hour.
The European Food Safety Authority (EFSA) Panel therefore considered that a conservative estimate of the lowest oral bolus dose of glycerol required for therapeutic effect was 125 mg/kg body weight per hour. The European Food Safety Authority (EFSA) Panel considered this dose would also be responsible for the side effects (nausea, headache and/or vomiting) observed in some patients.
Glycerol therapy in diabetics
Hyperosmolar non‐ketotic coma occurred in diabetic patients after repeated use of oral and intravenous glycerol. According to Sear , the non‐ketotic hyperosmolar hyperglycaemic state usually occurs in cases of maturity onset diabetes or pre‐diabetes and not in non‐diabetic subjects.
Food industry
In food and beverages, glycerol serves as a humectant, solvent, and sweetener, and may help preserve foods. It is also used as filler in commercially prepared low-fat foods , and as a thickening agent in liqueurs. Glycerol and water are used to preserve certain types of plant leaves .
As used in foods, glycerol is categorized by the Academy of Nutrition and Dietetics as a carbohydrate. The U.S. Food and Drug Administration (FDA) carbohydrate designation includes all caloric macronutrients excluding protein and fat. Glycerol has a caloric density similar to table sugar, but a lower glycemic index and different metabolic pathway within the body.
It is also recommended as an additive when using polyol sweeteners such as erythritol and xylitol which have a cooling effect, due to its heating effect in the mouth, if the cooling effect is not wanted.
Personal care applications
Glycerol is used in medical, pharmaceutical and personal care preparations, mainly as a means of improving smoothness, providing lubrication, and as a humectant. It is found in allergen immunotherapies, cough syrups, elixirs and expectorants, toothpaste, mouthwashes, skin care products, shaving cream, hair care products, soaps, and water-based personal lubricants. In solid dosage forms like tablets, glycerol is used as a tablet holding agent. For human consumption, glycerol is classified by the U.S. FDA among the sugar alcohols as a caloric macronutrient.
Glycerol is a component of glycerin soap. Essential oils are added for fragrance. This kind of soap is used by people with sensitive, easily irritated skin because it prevents skin dryness with its moisturizing properties. It draws moisture up through skin layers and slows or prevents excessive drying and evaporation.
Glycerol can be used as a laxative when introduced into the rectum in suppository or small-volume (2–10 ml) enema form; it irritates the anal mucosa and induces a hyperosmotic effect .
Taken orally (often mixed with fruit juice to reduce its sweet taste), glycerol can cause a rapid, temporary decrease in the internal pressure of the eye. This can be useful for the initial emergency treatment of severely elevated eye pressure in glaucoma .
Antifreeze
Like ethylene glycol and propylene glycol, glycerol is a non-ionic kosmotrope that forms strong hydrogen bonds with water molecules, competing with water-water hydrogen bonds. This interaction disrupts the formation of ice . The minimum freezing point temperature is about −36 °F (−38 °C) corresponding to 70% glycerol in water.
Glycerol was historically used as an anti-freeze for automotive applications before being replaced by ethylene glycol, which has a lower freezing point. While the minimum freezing point of a glycerol-water mixture is higher than an ethylene glycol-water mixture, glycerol is not toxic and is being re-examined for use in automotive applications.
In the laboratory, glycerol is a common component of solvents for enzymatic reagents stored at temperatures below 0 °C due to the depression of the freezing temperature. It is also used as a cryoprotectant where the glycerol is dissolved in water to reduce damage by ice crystals to laboratory organisms that are stored in frozen solutions, such as bacteria, nematodes, and mammalian embryos.
Vibration dampening
Glycerol is used as fill for pressure gauges to dampen vibration . External vibrations, from compressors, engines, pumps, etc., produce harmonic vibrations within Bourdon gauges that can cause the needle to move excessively, giving inaccurate readings. The excessive swinging of the needle can also damage internal gears or other components, causing premature wear. Glycerol, when poured into a gauge to replace the air space, reduces the harmonic vibrations that are transmitted to the needle, increasing the lifetime and reliability of the gauge.
Film industry
Glycerol is used by the film industry when filming scenes involving water to stop areas from drying out too quickly.
Glycerine is used—combined with water —to create a smooth smoky environment. The solution is vaporized and pushed into the room with a ventilator.
