DMannose

D-mannose is a simple sugar, an aldohexose with the chemical formula C6H12O6. It is the D-enantiomer of mannose and an epimer of D-glucose at carbon 2. In nature it occurs in small amounts in fruits such as cranberries, apples, and citrus, as well as in plant polysaccharides from which it can be hydrolyzed. It is often sold as a dietary supplement.

In solution it exists in multiple ring forms, including pyranose and furanose. In humans it is absorbed from the small intestine and largely filtered by the kidneys, where much of it is excreted in urine unchanged. A portion can enter cellular metabolism, being converted to mannose-6-phosphate for use in glycoprotein synthesis, but it is not an essential energy source. It is not a major participant in glycolysis.

Uses and evidence: D-mannose is marketed primarily for prevention of urinary tract infections, based on the idea that it binds to bacterial fimbriae and prevents adhesion to uroepithelial cells. It is not a replacement for antibiotics in active infections. Clinical evidence is mixed; some small studies report reduced recurrence in women with recurrent UTIs, while others find no significant benefit. Larger, high-quality trials are still needed.

Safety and regulation: D-mannose is generally well tolerated at commonly used doses; gastrointestinal upset may occur at higher doses. Diabetics or people with kidney impairment should consult a clinician before use. In many countries it is sold as an over-the-counter dietary supplement; it is not approved as a drug for UTIs and has no standardized dosing.