D-mannose powder for prophylaxis of recurrent urinary tract infections in women: A randomized clinical trial 

In 2014 researchers conducted a clinical trial with 308 women with a history of recurrent UTIs. Intervention was prophylactic treatment with either 2 g D-mannose powder, or 50 mg of the antibiotic nitrofurantoin, or in the third group no prophylactic treatment at all. There was a significantly greater rate of recurrent UTI in the group that received no prophylactic treatment. Of the participants given D-mannose, 14% had a recurrent UTI, compared to 20% in the antibiotic group, and 60% of the non-prophylactic treatment group. 

References:

Kranjcec B, Papes D, Altarac S. (2014). D-mannose powder for prophylaxis of recurrent urinary tract infections in women: a randomized clinical trial. World J Urol. 32(1): 79-84