What Is D-Mannose?

D-mannose is a type of sugar that can be found in certain fruits and vegetables, including cranberries, cabbage, and tomatoes. It's also produced in the body from glucose, another form of sugar. D-mannose is also called mannose.

As a dietary supplement, D-mannose is sometimes used to prevent urinary tract infections (UTIs) or bladder inflammation (cystitis) from infections. Though more research is needed, some studies suggest it could be helpful when used alongside standard treatment.

This article describes the purported uses of D-mannose, possible side effects, and what to look for in a supplement.

Purported Uses of D-Mannose

There is some evidence that D-mannose may prevent or treat UTIs. A number of small studies have suggested that D-mannose may help keep E. coli —the bacteria responsible for the vast majority of these infections—from sticking to the cells lining the urinary tract. More research is needed to confirm these effects. It should not be used to replace traditional treatment.

More than 7 million healthcare provider visits a year are due to this type of infection. Frequent UTIs are usually treated with a low-dose antibiotic taken for six months or longer.

UTI Prevention

Several studies have looked at the use of D-mannose to prevent returning UTIs:

• A study published in the World Journal of Urology examined the use of D-mannose compared with the antibiotic nitrofurantoin or no treatment for six months in 308 women with a history of recurrent UTIs. After one week of initial treatment, both people in the supplement group and the antibiotic group had a significantly lower risk of recurrent UTIs than the no-treatment group. Still, it did not prevent recurrent UTIs in all women in the study. The people in this study used a powder formulation of D-mannose.
• One systematic review of seven studies could not determine if taking D-mannose long-term compared with no treatment, other supplements, or antibiotics reduced the number of repeated UTIs.
• Another systematic review of eight studies showed that D-mannose appears to have a protective effect against recurrent UTIs compared with placebo. The review also suggested that D-mannose may be similarly effective to antibiotics for prevention. However, the researchers cautioned that not enough studies are available to confirm this, and existing studies are small in size and vary in study design and quality.

When used as a supplement, D-mannose may help prevent recurrent UTIs. However, more extensive, high-quality studies are needed.

UTI Treatment

It's important to remember that supplements should not replace traditional medical treatment. If you think you have a UTI, seek medical advice from a healthcare provider.

Studies have looked at whether D-mannose can help treat active UTIs. While some research has suggested the supplement may help when used in addition to antibiotics, remember that these studies are often small and low in quality.

The following studies examined the use of D-mannose for treating UTIs:

• A small study of 43 women found that D-mannose taken twice daily for three days during an infection 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 recurrence rate than those who took nothing.
• A systematic review of seven studies suggested that D-mannose may help improve UTI symptoms in the short term. However, the researchers noted that the findings were based on a limited number of small studies and should be considered cautiously.
• A review published in 2015 concluded that there is a lack of strong evidence that D-mannose—and other remedies like cranberry juice and vitamin C—should be used as a replacement for antibiotics in treating UTIs.

Research is ongoing and more studies are needed.

What Are the Side Effects of D-Mannose?

Common side effects of D-mannose reported in studies include:

• Bloating
• Loose stools
• Diarrhea

Precautions

Since D-mannose exits the body in urine, there is some concern that high doses may injure or impair the kidneys.

D-mannose can also potentially affect blood glucose levels in people with diabetes.

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, either.

You should not self-treat a UTI with D-mannose or otherwise avoid or delay standard care, as doing so can lead to serious complications, including a kidney infection and even permanent kidney damage.

Dosage: How Much D-mannose Should I Take?

While D-mannose is typically considered safe because it occurs naturally in many foods, doses higher than consumed through a normal diet may be toxic or otherwise harmful. In addition, little is known about the long-term safety of D-mannose at any dose.

There are currently no standard guidelines for D-mannose dosages. In studies, D-mannose dosages have ranged from as little as 420 milligrams per day to 3 grams in various supplement forms.

Consult your healthcare provider before taking D-mannose to confirm how much you should take.

Sources of D-mannose & What to Look For

D-mannose occurs naturally in:

• Cranberries
• Black and red currants
• Peaches
• Green beans
• Cabbage
• Tomatoes

D-mannose supplements are available in capsule or powder form. D-mannose powder is mixed with water or unsweetened juice and taken as a liquid.

It's important to remember that dietary supplements haven't been tested for safety and are largely unregulated in the United States.

When shopping for supplements, look for products certified by ConsumerLab, The U.S. Pharmacopeial Convention, or NSF International. These organizations don't guarantee a product is safe or effective, but their seal indicates that a supplement has undergone testing for quality.

Summary

Preliminary studies suggest that D-mannose holds promise as a way to help prevent UTIs. However, larger high-quality studies are needed to confirm the findings and the safety of D-mannose supplements.

If you're still thinking of trying D-mannose to prevent UTIs, talk with your healthcare provider first to weigh the pros and cons and decide whether it's a good option for you.