What Is D-Mannose?

D-mannose is a type of sugar found in certain fruits and vegetables such as cranberries, cabbage, and tomatoes. D-mannose is also produced in the body from glucose, another form of sugar.

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

This article will describe some preliminary studies that support the use of D-mannose, possible side effects, and what to look for in a supplement.

What Is D-Mannose?

D-mannose is a kind of sugar naturally found in some fruits and vegetables. Good dietary sources of D-mannose include:

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

D-mannose may have health benefits for people who experience frequent urinary tract infections (UTIs), but more scientific evidence is needed.

D-Mannose Health Benefits

A number of small studies have suggested that D-mannose may help keep E. coli —the bacteria responsible for the vast majority of UTIs—from sticking to the cells lining the urinary tract. It is possible that this could help prevent and treat UTIs, but more research is needed.

Frequent UTIs are usually treated with a low-dose antibiotic taken for six months or longer. While this may be effective, it can lead to antibiotic resistance.

Antibiotic resistance occurs when an antibiotic is used often enough that the bacteria it's intended to kill become resistant to the medication, making it ineffective.

Given this possibility, and the fact that more than 7 million healthcare provider visits a year are due to this type of infection, having a non-antibiotic treatment option is appealing.

Prevention

A study published in the World Journal of Urology in 2014 examined the use of D-mannose to prevent returning urinary tract infections.

After one week of initial treatment with antibiotics, 308 women with a history of recurrent UTIs took either D-mannose powder, the antibiotic nitrofurantoin, or nothing for six months.

During this period, the rate of recurrent UTIs was significantly higher in women who took nothing compared to those who took D-mannose or the antibiotic.

The study concluded that the risk of recurrence was the same for the supplement group as the antibiotic group.

However, 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.

During an Infection

D-mannose has also been tested in people with active UTIs. A small study of 43 women published in 2016 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 rate of recurrence than those who took nothing.

Although D-mannose shows promise in these preliminary studies, 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.

Possible Side Effects of D-Mannose

Common side effects of D-mannose include:

• Bloating
• Loose stools
• Diarrhea

As D-mannose exits 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 it.

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.

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

Dosage and Preparation

As a supplement, D-mannose is available as a powder or in capsule form. D-mannose powder is typically dissolved in liquid and taken as a drink. 

Little is known about the long-term safety of D-mannose or at what dose the supplement may be considered harmful or toxic.

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

Dosages as high as 2 grams daily to prevent UTIs and 3 grams to treat UTIs have been used in studies.

What to Look For

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

When shopping for supplements, look for products that have been 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.