D-Mannose occurs naturally in microbes, plants, animals and fruits including apples, peaches and oranges as a simple sugar. It is also found naturally in the human body. Preliminary European clinical trials have shown that D-mannose may also treat or prevent urinary tract infections (UTIs). It appears the supplement stops certain bacteria from clinging to the bladder walls. 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 urinary tract infection.