Urinary Tract Infections:Cranberry Helps the Body Evade Pesky Bacteria

Chances are you expect the doctor’s diagnosis. You’ve been down this road before, and the symptoms are hard to mistake: a burning sensation when you urinate, frequent urination in small amounts, and lower abdominal and back pain. You have a urinary tract infection, and the discomfort can be almost unbearable.

In the United States, urinary tract infections account for a significant number of the bacterial infections suffered each year. Perhaps only strep throat accounts for more. By some estimates, as many as 50 million cases of urinary tract infections are treated annually. Although these infections aren’t considered life-threatening or even a significant health risk for most people, their financial toll is enormous. Medication for each episode can cost about $30 and a visit to a physician, at least $40. Include time missed from work, and urinary tract infections cost billions of dollars a year.

Health-care providers have relied primarily upon antibiotics to treat urinary tract infections. However, increasing concern about bacterial resistance to antibiotics and rising interest in alternative medicine have prompted doctors and researchers to seek new treatments. Recent studies suggest that cranberry (Vaccinium macrocarpon), long reputed to have antibacterial properties, may have the potential to prevent or heal these expensive and painful infections.

Cranberry then and now

As early as the 1840s, German researchers were examining the connection between European cranberry species and urinary tract infections. They found that the urine of people who ate cranberries contained a chemical called hippuric acid. By the turn of the century, U.S. researchers were speculating that this attribute meant that cranberries could acidify urine and thereby prevent infection. By the 1960s, however, the idea of using cranberry to treat such infections had fallen out of favor because researchers failed to show that it increased urine acidity enough to prevent illness. Today, researchers are again addressing the relationship between cranberries and a healthy urinary tract, only this time they are focusing on a different action: cranberry’s potential to keep bacteria from attaching to urinary tract walls.

How infection begins

These infections are generally divided into three categories. Urethritis is an infection of the urethra, the canal that transports urine from the bladder and in males also serves as a genital duct. The infection is usually caused by viruses transmitted during intercourse. Cranberry can’t be used to prevent or treat this condition because it is not effective against viral infections. Cystitis is an infection of the urinary bladder, the organ that stores urine. Pyelonephritis, or kidney infection, results when the bacteria in the bladder migrate to the kidneys. This type of infection is the most serious of the three; it is often accompanied by fever, chills, nausea, and severe back pain. Current cranberry research is focusing on cystitis and pyelonephritis because they are caused by the bacteria Escherichia coli (E. coli).

E. coli serve a positive purpose in the large intestine, where they break down the by-products of digestion. However, they also are responsible for about eighty-five percent of all urinary tract infections. E. coli, which enter through the perineum and travel through the urethra up to the bladder, attach themselves to cells in the bladder wall, where they reproduce, colonize, and cause a bladder infection. Because this infectious process starts to destroy the superficial lining of the bladder and disrupts the small capillaries, urine of infected individuals often contains blood. If the infection progresses, the E. coli will then travel up the urethers and infect the kidneys.

How cranberry works

Tamms-Horsfall glycoprotein, a natural substance present in the urine of some individuals, has the ability to attach itself to the E. coli bacteria and inhibit them from attaching to the bladder wall. Individuals with enough Tamms-Horsfall glycoprotein are unlikely to get a urinary tract infection from E. coli. However, those who lack or have low levels of this natural substance are more susceptible.

In 1994, researchers at Weber State University in Utah discovered that cranberry contains a substance similar in activity to the Tamms-Horsfall glycoprotein. While they have yet to release the substance name until they obtain patent rights, general information is available about how it works. Much like natural glycoprotein, the substance can inhibit the attachment of E. coli bacteria to the bladder wall. In tests where cranberry was added to a petri dish along with E. coli bacteria and bladder cells, the addition of the cranberry substance kept the bacteria from attaching to bladder cells.

Additionally, a 1994 Harvard University study involving 153 elderly women with histories of repeated urinary tract infections showed that regular consumption of cranberry juice cocktail can decrease the incidence of urinary tract infections. In a clinical trial yet to be published from Weber State, the same conclusion was drawn using a concentrated cranberry product. This product, in dehydrated, capsule form, is equivalent to twelve to sixteen 6-ounce glasses of cranberry juice.

Using cranberry

Our bodies do have natural barriers against urinary tract infections. In men, the urethra is up to 10 inches long with natural bends, both of which make it difficult for bacteria to reach the bladder. In females, the perineum helps prevent bacteria from entering the urethra. Females are at a disadvantage, however, because the perineum can be damaged or irritated by tight clothing, intercourse, poor hygiene, or bubble baths, and thus allow bacteria to make their way to the bladder. In addition, the female urethra is only 2 inches long and straight, making it easy for bacteria to reach the bladder. If a female infant or young girl has had two or three infections, X-rays of her urinary tract are in order to rule out possible anatomical abnormalities. In the case of young boys, X-rays are in order with the first infection to ascertain whether the urinary tract is intact and functioning properly.

Females also are more likely than males to get a second urinary tract infection, and within as little as two weeks of the first flare-up. During the initial infection, the lining of the bladder is injured, making it more susceptible to new E. coli seeking to attach themselves before the lining has a chance to heal. As such, some women have recurrent urinary tract infections simply because their bladder never really has a chance to heal.

When I see a patient with an acute (recent) urinary tract infection, I use several avenues of treatment. This may include a single or one-day dose of antibiotic to kill existing bacteria. I combine this with one pill of a concentrated cranberry capsule two times a day for at least one month to protect the bladder against reinfection while it heals. Alternatively, a short-term dose of a natural substance such as thyme (Thymus spp.), goldenseal (Hydrastis canadensis), or queen of the meadow (Filipendula ulmaria) can be taken instead of antibiotics to eliminate bacterial growth in the bladder.

When one of my patients has a series of urinary tract infections, I recommend the same treatment, except the daily dose of cranberry capsule should be taken for three to four months. If the patient suffers no infections during that time, I take her off the product. Some patients will experience subsequent but infrequent infections that can be easily treated. However, others will suffer frequent recurrences. For them, I recommend maintaining the daily dose of a cranberry capsule, possibly for the rest of their lives.

If you enjoy the flavor of cranberry juice, one way to reap its benefits is to drink two to three glasses a day. Most cranberry juice or cocktails contain between 10 and 20 percent cranberry, and for some individuals such amounts are effective enough to prevent urinary tract infections. Although the benefits of drinking cranberry juice outweigh the negative effects of the sugar it contains, for people who are concerned about sugar, such as diabetics, sugar-free juice is available. If you don’t find the cranberry flavor appealing or you require a higher cranberry concentration, many health-food stores carry concentrated cranberry capsules.

Why cranberry holds promise

Currently, the only alternative to cranberry for preventing urinary tract infections is to take an antibiotic regularly. This, however, is not always a good solution because of the risk of allergic reaction and of developing strains of bacteria resistant to antibiotics. On the other hand, the risk of allergic reaction to cranberry is negligible, and the bacteria have not been shown to be resistant to it. Thyme, goldenseal, and queen of the meadow are not effective as preventives, and some, such as goldenseal, should not be taken for long periods of time.

Cranberry also may be effective for patients who have difficulty emptying their bladder, such as men with enlarged prostates or patients with neurologic abnormalities including stroke or spina bifida. When urine remains in the bladder, bacteria have a greater chance of attaching to the bladder lining. Individuals with catheters also face an increased risk because bacteria can be introduced any time a foreign object enters the bladder. Although I know of no studies on this group of patients, it seems likely that cranberry may offer them badly needed relief.

D. Paul Barney is a family practice and emergency room doctor in Layton, Utah. He also is an adjunct professor at Weber State University and author of Clinical Applications of Herbal Medicine (Woodland Publishing, 1996).


Avorn, J.M., M. Monane, J.H. Gurwitz, R.J. Glynn, I. Choodnovskiy, and L.A. Lipsitz. “Reduction of bacteriuria and pyuria after ingestion of cranberry juice”. Journal of American Medical Association 1994, 271:751 – 754.

Fowler, J.E. “Urinary Tract Infections in Women”. Urologic Clinics of North America 1986, 13(4):673 – 683.

Connection error. Connection fail between instagram and your server. Please try again
Written by D. Paul Barney MD

Explore Wellness in 2021