Get 500 mg per capsule of D-Mannose from NOW Foods'. D-Mannose is a simple sugar that occurs naturally in some plants, including cranberries. D-Mannose interferes with particle attachment and promotes a healthier urine flow. Although small amounts of D-Mannose are metabolized by the human body, much of it is rapidly excreted in the urine. Because insubstantial amounts of D-Mannose are used by the body, it does not interfere with blood sugar regulation.