Dosage of Cranberry Extract for UTIs

“The New England Journal of Medicine” reports that every year 11 percent of American women seek medical care for a urinary tract infection, UTI. If you are female, your lifetime risk for developing a UTI is 60 percent. Many of the bacteria that cause these infections have become resistant to commonly prescribed antibiotics. Cranberry juice has been used for decades as an alternative remedy for UTIs, but the dosage needed to confer benefit is unclear, and cranberry products are not universally accepted as an effective therapy. Consult a doctor before using cranberry for UTI.

How UTIs Get Started

Your urinary tract is normally a relatively sterile environment. However, bacteria can gain access to your bladder by ascending through your urethra, which is the tube that drains urine from your bladder. If urine is retained in your bladder for extended periods of time, if your urethra becomes irritated or inflamed, or if the normal protective barriers that coat the lining of your bladder break down, bacteria can adhere to the interior of your bladder and begin reproducing. Cranberry juice may prevent bacteria from "sticking" to your bladder wall.

Cranberry Juice or Extract?

Is D-mannose Better Than Cranberry for UTI?

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Early clinical studies, such as a 1994 trial in “The Journal of the American Medical Association,” used commercially-prepared beverages to test cranberry's effects on bacterial adhesion. Test subjects had to consume at least ten ounces of cranberry juice daily throughout the study period; beneficial effects were not really noticeable until 4 to 8 weeks into the trial. Subsequent studies have not shown significant differences between cranberry juice, tablets and capsules, according to a 2008 “Cochrane Database Review.”

Prevention or Cure?

Most of the studies involving cranberries' effects on UTIs have been designed to evaluate their preventive benefits. It is generally assumed that an established UTI is less likely to respond to the administration of cranberry products, since cranberries primarily interfere with bacterial adhesion, rather than directly kill them. A 2009 review in “Drugs” confirms that, while there is good evidence to support the use of cranberries for preventing UTIs, there is no conclusive evidence that cranberries are effective for treating established infections.

Cranberry Dosage Uncertain

Risks of Cranberry Pills

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Expert reviews of available medical literature have not established the optimal dose of cranberry preparations for preventing UTIs. However, most studies have been conducted with the equivalent of 8 to 10 ounces of cranberry juice daily. Since cranberry juice often causes gastrointestinal upset, capsules and tablets are popular alternatives to beverage preparations. Cranberry products can interact with warfarin, leading to increased bleeding tendencies. If you have frequent UTIs and would like to try cranberry to prevent them, talk with your physician.