Reviewed: Kessler T, Jansen B, Hesse A. Effect of black currant-, cranberry- and plum juice. European Journal of Clinical Nutrition 2002;36:1020-1023.
High fluid intake is widely regarded as the most important preventive treatment for kidney stones, reducing the concentration of constituent ions and saturation of stone-forming salts. The most suitable fluids for this purpose are mineral water, orange juice, apple juice, and fruit and herbal teas. Patients with a history of kidney stones should avoid fluids that contain stone-forming agents and promoters; these include coffee, black tea, alcohol, and cola soft drinks. Cranberry juice has been used extensively to prevent and treat urinary tract infections, and small studies on the effects of ingestion of black currant juice and prunes (dried plums) have shown an acidifying effect on urine in humans. Various shortcomings in these studies and a lack of scientific evidence have led these researchers to evaluate the influence of these three juices on urinary composition and kidney stone formation.
Twelve healthy male subjects (ages 18-38 years) with no history of kidney disorders participated in four consecutive trial phases of five days each. All phases were equivalent in dietary intake and included a four-day adaptation period during each phase before the experimental load on the fifth day. Creatinine was measured on days 1-4 to ensure compliance with the diet, and 24-hour urine samples were collected each day. Day five of each phase was the experimental day with consumption of 330 ml of either mineral water (control, assumed to have no effect on urinary composition), or juice from either plums (Prunus domestica L., Rosaceae), cranberries (Vaccinium macrocarpon Aiton, Ericaceae), or black currants (Ribes nigrum L., Grossulariaceae).
Changes were noted in several urinary parameters following consumption of each juice. Black currant juice significantly alkalized the urine (P < 0.01), increased citric acid excretion (P < 0.01), and oxalic acid excretion (P < 0.05). Cranberry juice significantly acidified the urine (P < 0.05) and showed a small, not statistically significant decrease in citric acid excretion. Oxalic acid excretion was significantly increased after ingestion of cranberry juice (P < 0.05). Black currant juice did not significantly affect the relative supersaturation for calcium oxalate, uric acid, brushite, and struvite, but cranberry juice significantly increased the relative supersaturation of uric acid (P < 0.05) and decreased the relative supersaturation of struvite and brushite. Plum juice had no statistically significant effect on any of the urinary parameters measured. Excretion of calcium, magnesium, and uric acid were not significantly changed by any of the experimental juices.
The increased excretion of oxalic and citric acids with black currant juice was attributed to the content of these acids and ascorbic acid (which is metabolized to oxalic acid) in the consumed juice. The alkalizing effect of black currant juice did not decrease the relative supersaturation of calcium oxalate and uric acid as would be expected, which the authors attributed to the increase in oxalic acid excretion. The decrease in pH with cranberry juice was expected and Is associated with increased risk of uric acid stone formation; however, the relative supersaturation for struvite and brushite were slightly decreased. The authors speculate that the effect of cranberry juice might be larger if more juice was ingested.
The authors conclude that black currant juice could be used as a preventive and treatment for uric acid stones due to its alkalizing effect on the urine. Cranberry juice could be of use when acidification of the urine is indicated, as with apatite, brushite, and struvite stones as well as with urinary tract infection.
This well-designed study compensated for the perpetual problem of quantifying food and beverage intake by requiring subjects to consume a standardized diet, followed by biochemical and physical measurements to ensure compliance. Adequate research and annotation supported the study topic. The claims made for black currant and cranberry juices were not completely substantiated by the results; however, the authors noted that this study was conducted in healthy subjects and suggested that further research into the usefulness of these juices should be done in patients with a history of kidney stone formation.
However, it should be noted that there are different types of kidney stones. If possible, stones that are passed should be caught in a strainer and then analyzed for their content. Most are calcium, but a minority are uric acid (an indication of gout) or oxalic acid (an inherited trait). Calcium kidney stones are best treated with acidic drinks, but the acid stones need basic (bicarbonate, etc.) drinks to dissolve. Treating uric acid and oxalic acid kidney stones with acidic beverages is ineffective. Uric acid kidney stones comprise only 20-30 percent of kidney stones, yet universal statements about kidney stone treatment must be considered in this context.
By Diane S. Graves, MPH, RD