Clinical Studies

A highly publicized study examined the effect of cranberry juice cocktail on bac-teriuria and pyuria in 153 elderly women (Avorn et al., 1994). By the second month of the study, the placebo group had three times the number of bacteria-contaminated urine samples as the cranberry group. Although the differences varied with time, the differences between groups became smaller after 6 months. Some patients in each group (16, placebo; 8, cranberry) were treated with antibiotics for UTIs during the course of the study. A major critique of this study is that the placebo group had a much greater number of patients who had been treated in the past 6 months for UTIs. This group may have been predisposed to development of such infections, thereby skewing the results in favor of the cranberry treatment. However, the researchers did account for the difference in groups with statistical analyses. Interestingly, all cranberry beverage samples inhibited bacterial adhesion in vitro, while none of the placebo beverages inhibited adhesion.

In a recent study involving a blend of juices from European cranberry (V. oxy-coccus) and lingonberry, 150 women were assigned to drink the juice, a probiotic beverage, or no treatment for 6-12 months, depending upon the treatment (Kontiokari et al., 2001). Although the study was not placebo controlled, the juice significantly delayed the onset of UTI recurrence (Figure 3.5).

Although most studies have reported the effect of beverages, capsules containing 400 mg of cranberry solids were tested in a small study (Walker et al., 1997). Only ten women completed the study, which involved consumption of the cranberry supplement or a calcium placebo for 6 months after diagnosis and treatment with antibiotics of a UTI. The researchers concluded that the cranberry capsules were effective in reducing development of UTIs in young women prone to such infections.


Figure 3.5 Incidence density of urinary tract recurrence in 150 women in 3 treatment groups (N = 50).* indicates significant difference (p = 0.03). (Source: Kontiokari et al. 2001. Brit. Med. J., 322(7302):1571-1575. With permission.)

A review article for nurses summarized situations in which cranberry juice cocktail could be used: as a preventative measure for persons prone to UTIs, as part of the treatment for UTIs, to acidify urine to prevent calcium stone formation and improve urine odor, and to reduce mucus formation in patients with urostomies or catheters (Leaver, 1996). Fleet (1994) suggested that the effect of cranberry juice on intestinal flora may be an important first step in reducing UTIs, since bladder contamination with fecal bacteria is common. Significantly fewer bacteria were found adhering to bladder cells from 15 persons with spinal cord injuries who had drunk three glasses of cranberry juice (Reid et al., 2001). Howe and Bates (1987) questioned the high cost of cranberry juice and raised the issue of taste. Persons who dislike the taste of cranberry juice will be reluctant to drink it, despite potential health benefits. Table 3.2 lists other conditions that may be improved by cranberry or blueberry consumption.

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