The Health Benefits of D-Mannose

D-mannose (or mannose) is a type of sugar found in a number of fruits and vegetables, including cranberries, black and red currants, peaches, green beans, cabbage, and tomatoes. It's also produced in the body from glucose, another form of sugar.

As a dietary supplement, D-mannose is often touted as a natural way to treat and prevent a urinary tract infection (UTI) or bladder infection (cystitis). Though more research is needed, preliminary studies suggest that the supplement could be well worth exploring. Since treatment for frequent UTIs is long-term low-dose antibiotic use (six months or longer), having a non-antibiotic treatment for this type of infection—which accounts for more than six million doctor visits a year—would help prevent antibiotic resistance.

A number of smaller studies have suggested that D-mannose may hinder bacteria from adhering to the cells lining the urinary tract. Research published in 2008 in the journal PLoS One demonstrated that D-mannose can help stop E. coli (the bacteria responsible for the vast majority of UTIs) from sticking to cells in the urinary tract.

A study published in the World Journal of Urology in 2014 examined the use of D-mannose to prevent recurrent urinary tract infections. After one week of initial treatment with antibiotics for an acute UTI, 308 women with a history of recurrent UTIs took D-mannose powder, the antibiotic nitrofurantoin, or nothing for six months.

During the six-month period, the rate of recurrent UTIs was significantly higher in women who took nothing compared to those who took D-mannose or nitrofurantoin. Fewer side effects were reported with D-mannose compared to the antibiotic. The main one noted was diarrhea, which occurred in 8% of women taking D-mannose.

A small pilot study of 43 women published in 2016 found that D-mannose administered twice daily for three days followed by once a day for 10 days resulted in a significant improvement in symptoms, UTI resolution, and quality of life. Those who received D-mannose for six months following treatment had a lower rate of recurrence than those who took nothing.

Although D-mannose shows promise, a review of studies published in 2015 concluded that D-mannose (and other non-pharmaceutical remedies like cranberry juice and vitamin C) are ill-suited to replace antibiotics in treating UTIs.

Common side effects of D-mannose include bloating, loose stools, and diarrhea. As D-mannose is excreted from the body in urine, there is also some concern that high doses may injure or impair the kidneys.

Since D-mannose can alter your blood sugar levels, it's crucial for people with diabetes to take caution when using D-mannose supplements. Not enough is known about the safety of the supplement during pregnancy or breastfeeding, so it should be avoided. Children shouldn't take D-mannose as well.

As a rule, self-treating a UTI with D-mannose, or avoiding or delaying standard care, is unadvised as it can lead to serious complications, including a kidney infection (pyelonephritis) and even permanent kidney damage.

Little is known about the long-term safety of D-mannose or at what dose the supplement may be considered harmful or toxic. But dosages as high as two grams daily to prevent UTIs and three grams to treat UTIs have also been used in studies.

While D-mannose is typically considered safe because it occurs naturally in many foods, doses higher than what is consumed through normal diets may pose unknown health problems; it's simply not known at this stage.

It's important to keep in mind that dietary supplements haven't been tested for safety and are largely unregulated. When shopping for supplements, look for products that have been certified by ConsumerLabs, The U.S. Pharmacopeial Convention, or NSF International. These organizations don't guarantee a product is safe or effective, but they indicate that it's undergone testing for quality.

If you're still thinking of trying D-mannose to treat a UTI (or are considering it for preventative purposes), talk with your doctor first to weigh the pros and cons and decide whether it's the best option for you.