Mannose is a simple sugar (monosaccharide), so it belongs to simple carbohydrates. It is composed of the same elements (C6H12O6) as glucose, but has a different arrangement of atoms [1]. The chemical form that appears in foods and most supplements is called D-mannose.

The name origin: the Greek manna = food miraculously supplied to the Israelites in the wilderness; -ose denotes sugar.

Is mannose an essential nutrient?

Mannose is not an essential nutrient, which means you do not need to get it from food to be healthy; mannose can be produced in your body from glucose [3].

Mannose Functions in the Human Body

  • In the human body, mannose can be converted to glucose and provide 2-5 kilocalories per gram of energy [nutrition f. labels].
  • Mannose contributes to the synthesis of glycoproteins, which mainly appear in the cell membranes [3].

Dietary Sources of Mannose

In foods, mannose appears as part of complex carbohydrates such as galactomannans (guar gum, carob gum or locust bean gum, fenugreek gum, tara gum) and glucomannans (konjac gum).

Mannose can be found in fruits (peaches, apples, oranges, blueberries, black currants, cranberries), legumes (green beans, kidney beans, lima beans, soybeans), vegetables (cabbage, turnip, tomatoes), ivory nuts, Aloe vera and baker’s yeast [2,3,10,11,12]. The amount of mannose that can be absorbed from these foods in not known [3,4].

Mannose Syrup

Mannose syrup is a term used for konjac gum or glucomannan.

D-Mannose Supplements

Oral mannose supplements have been successfully used in the treatment of a rare genetic disease called carbohydrate deficient glycoprotein syndrome (CDGS) type 1b [5,6].

Mannose is partially excreted in the urine [3]. Some websites advertise D-mannose as a supplement that can prevent or even treat lower urinary tract infections (bladder, urethra) caused by E. coli bacteria, treat cancer and boost immunity, but no clinical studies on humans have been done so far to support such claims.

Side Effects

Side effects of mannose supplements may include bloating, diarrhea and (when used in high doses) kidney damage [7] and, maybe, birth defects [13].

D-mannose supplements should not be used during pregnancy and breastfeeding and in diabetes mellitus [7].

Cranberry Juice

Cranberry juice, which is high in mannose, is believed by some people to prevent urinary tract infections (UTI), but in one study involving 230 young women, cranberry juice was even less effective than placebo [8]. However, several other clinical trials have shown that cranberry juice may prevent UTI caused by E. coli bacteria [9,14], but the active substance in cranberry juice might be tannins [15], not mannose. Antibiotics are still a recommended treatment for established urinary infections.

  1. Monosaccharide mass and structure
  2. Leung MYK et al, 2004, Chemical and biological characterization of a polysaccharide biological response modifier fromAloe vera L. var. chinensis (Haw.) Berg  Glycobiology
  3. Herman RH, 1971, Mannose metabolism  The American Journal of Clinical Nutrition
  4. Alton G et al, 1998, Direct utilization of mannose for mammalian glycoprotein biosynthesis  Glycobiology
  5. Hendriksz CJ et al, 2001, Successful treatment of carbohydrate deficient glycoprotein syndrome type 1b with oral mannose  Archives of Diseases in Childhood
  6. Niehues R et al, 1998, Carbohydrate-deficient Glycoprotein Syndrome Type Ib  PubMed Central
  7. D-mannose  RxList
  8. Larson NF, 2010, Cranberry Juice May Not Prevent Urinary Tract Infection  Medscape
  9. Howel AB et al, 2010, Dosage effect on uropathogenic Escherichia coli anti-adhesion activity in urine following consumption of cranberry powder standardized for proanthocyanidin content: a multicentric randomized double blind study  PubMed Central
  10. Lu Y et al, 1993, Isolation of oligomannose-type glycans from bean glycoproteins  PubMed
  11. Takata R et al, 2005, Immunostimulatory effects of a polysaccharide-rich substance with antitumor activity isolated from black currant (Ribes nigrum L.)  PubMed
  12. Duarte-Vásquez MA et al, 2003, Monosaccharide composition and properties of a deglycosylated turnip peroxidase isozyme  PubMed
  13. D-mannose  University of Michigan, Health System
  14. 2010, New evidence on how cranberry juice fights bacteria that cause urinary tract infections  American Chemical Society
  15. Hisano M et al, 2012, Cranberries and lower urinary tract infection prevention  PubMed Central

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