D-mannose is a type of sugar that’s related to the better-known glucose. These sugars are both simple sugars —that is, they consist of just one molecule of sugar. As well, both occur naturally in your body and are also found in some plants in the form of starch.

Several fruits and vegetables contain D-mannose, including:

  • cranberries (and cranberry juice)
  • apples
  • oranges
  • peaches
  • broccoli
  • green beans

This sugar is also found in certain nutritional supplements, available as capsules or powders. Some contain D-mannose by itself, while others include additional ingredients, such as:

  • cranberry
  • dandelion extract
  • hibiscus
  • rose hips
  • probiotics

Many people take D-mannose for treating and preventing urinary tract infections (UTIs). D-mannose is thought to block certain bacteria from growing in the urinary tract. But does it work?

E. coli bacteria cause 90 percent of UTIs. Once these bacteria enter the urinary tract, they latch on to cells, grow, and cause infection. Researchers think that D-mannose works for a UTI by preventing these bacteria from latching on.

After you consume foods or supplements containing D-mannose, your body eventually eliminates it through the kidneys and into the urinary tract. While in the urinary tract, it can attach to the E. coli bacteria that may be there. As a result, the bacteria can no longer attach to cells and cause infection.

There isn’t much research on the effects of D-mannose when taken by people who have UTIs, but a few early studies show that it might help.

A 2013 study evaluated D-mannose in 308 women who had frequent UTIs. D-mannose worked about as well as the antibiotic nitrofurantoin for preventing UTIs over a 6-month period.

In a 2014 study, D-mannose was compared to the antibiotic trimethoprim/sulfamethoxazole for treatment and prevention of frequent UTIs in 60 women. D-mannose reduced UTI symptoms in women with an active infection. It was also more effective than the antibiotic for preventing additional infections.

A 2016 study tested the effects of D-mannose in 43 women with an active UTI. At the end of the study, most women had improved symptoms.

A lot of different D-mannose products are available. When deciding on which to use, you should consider three things:

  • whether you’re trying to prevent an infection or treat an active infection
  • the dose you’ll need to take
  • the type of product you want to take

D-mannose is typically used for preventing a UTI in people who have frequent UTIs or for treating an active UTI. It’s important to know which of these you are using it for because the dosage will differ.

The best dose to use isn’t entirely clear, however. For now, the doses that have been used in research are recommended:

  • For preventing frequent UTIs: 2 grams once daily, or 1 gram twice daily.
  • For treating an active UTI: 1.5 grams twice daily for 3 days, and then once daily for 10 days; or 1 gram three times daily for 14 days.

D-mannose comes in capsules and powders. The form you choose mainly depends on your preference. You might prefer a powder if you don’t like to take bulky capsules or want to avoid the fillers included in some manufacturers’ capsules.

Keep in mind that many products provide 500-milligram capsules. This means that you may need to take two to four capsules to get the desired dose.

To use D-mannose powder, dissolve it in a glass of water, and then drink the mixture. The powder dissolves easily, and the water will have a sweet taste.

Most people who take D-mannose don’t experience side effects, but some might have loose stools or diarrhea.

If you have diabetes, talk with your doctor before taking D-mannose. It makes sense to be cautious since D-mannose is a form of sugar. Your doctor might want to monitor your blood sugar levels more closely if you take D-mannose.

If you have an active UTI, don’t delay in talking with a healthcare provider. Although D-mannose might help treat infections for some people, the evidence isn’t very strong at this point. Delaying treatment with an antibiotic that has been proven to be effective can result in a more serious infection of the kidneys and blood.

More research needs to be done, but D-mannose appears to be a promising nutritional supplement that may be an option for treating and preventing UTIs, especially in people who have frequent UTIs. Most people who take it don’t experience any side effects.

Talk with your doctor if you have an active UTI. Although D-mannose might help treat a UTI for some people, it’s important to follow proven methods of treatment to prevent the development of a more serious infection.

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