D-mannose is used to treat a rare disease called carbohydrate-deficient glycoprotein syndrome type 1b.
This disease is passed down through families. It makes you lose protein through the intestines. Some reports say D-mannose slows down this protein loss and makes your liver work better. It may also reduce bleeding disorders and low blood sugar in people with this disease.
Scientists think that the bacteria stick to the sugar instead. This helps the bacteria leave the body through your urine. Fewer bacteria in the bladder lowers your risk of a UTI. However, no studies of D-mannose have been done in people to determine if it effectively treats or prevent UTIs.
Some studies suggest D-mannose may play a useful role as a "prebiotic." Prebiotics are substances that may help your body by stimulating the growth of "good" bacteria in your digestive system.
In some lab studies and studies in mice, D-mannose components were shown to increase the growth of "good" bacteria. This suggests D-mannose may have some use for people with dysbiosis, an imbalance in good and bad bacteria.
Always tell your doctor about any supplements you are taking, including natural ones and those bought without a prescription. That way, your doctor can check on any potential side effects or interactions with any medications.