One-fifth of women who experience a urinary tract infection (UTI) will get reinfected. UTIs are the second most common infection afflicting close to ten million people a year. The commonly prescribed treatment is the use of antibiotics but in the case of recurrent UTIs excessive antibiotic use can lead to antibiotic resistance and some undesirable side effects. To avoid recurrent UTIs and excessive antibiotic use some doctors are recommending patients to consume cranberries.
Understanding What Causes a Urinary Tract Infection
UTI’s start when E. coli normally found in the digestive tract start growing and multiplying on the urethra opening. The bacteria can then spread up to the bladder and in extreme cases the bacteria spreads to the kidneys. The bacteria first adhere to the uroepithelial cells via fimbriae.
Next the bacteria invade the cells in search of the cell’s iron and nutrients. The body reacts by increasing blood flow to the area causing inflammation. The bacteria have the ability to move up the urinary tract to infect other sections of the urinary tract. The immune system and antibiotics both work by destroying the bacteria; however some bacteria have the ability to resist the body’s immune system and the antibiotics.
Cranberry juice seems to work by deterring against further infections. Its mode of action against a urinary tract infection has been intensively studied.
Cranberry Juice Blocks Bacteria from Attaching to UTI Cells
Cranberry juice barely alters the urine's pH and does not have antibiotic properties. According to a study done on cranberry products, researchers found that certain phytochemicals found in cranberries block the bacteria (in this study E. coli) from binding to the uroepithelial cells (Paola A. Pinzón-Arango, Yatao Liu, and Terri A. Camesano “Role of Cranberry on Bacterial Adhesion Forces and Implications for Escherichia coli—Uroepithelial Cell Attachment" J Med Food 12 (2) 2009). The bacteria bind via fimbriae found on their cell surface to receptors on the uroepithelial cells. Cranberry juice extracts were found to block the bacteria from attaching.
Anthocyanins in Cranberry Juice can be Found Intact in Urine
To prove that cranberry juice's anthocyanins are absorbed by the body, a study took 11 healthy volunteers and had them consume cranberry juice. Over a 24-hour period, their urine was tested for anthocyanins. (Ohnishi, R et al.,“Urinary Excretion of Anthocyanins in Humans after Cranberry Juice Ingestion” Bioscience, Biotechnology, and Biochemistry Vol. 70 (2006), No. 7 pp.1681-1687). The study found that the anthocyanins proposed to help in UTIs were absorbed into the blood and then transported unmetabolized into the urinary tract.
Cranberries contain a unique group of anthocyanins that have been credited to staving off UTIs. Initially it was thought that the acidity of the fruits deterred the growth of the E. coli, however research has showed that the anthocyanins found in the cranberries effectively block the bacteria from attaching to the uroepithelial cells. There are however still many unanswered questions about the efficacy of cranberries:
- Best dose of cranberry juice to elicit the best protective effect
- Effects of cranberry juice with other medications, and
- Form of the cranberries works best (juice, fruits or capsules).
Studies are still ongoing to answer these questions.
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