An increase in fluid intake is routinely recommended for patients who have had a kidney stone in order to decrease the likelihood of recurrence. Higher fluid intake leads to increased urinary volume which, in turn, leads to a decreased concentration of lithogenic factors, thus decreasing the rate of stone formation. But, does the type of fluid make a difference or are all fluids alike in their ability to reduce stone formation?
In a prospective cohort study with 8 years of follow up done a the Brigham and Women's Hospital, and Harvard Medical School, in Boston, 81,093 women in the Nurses' Health Study were assessed by food questionnaires. Over the 8-year follow up, 719 cases of kidney stones were documented. After controlling for other risk factors, the researchers compared the relative risk for stone formation for women in the highest quintile of total fluid intake compared with women in the lowest quintile. There was a definite increase in the risk for stones in women with the lowest fluid intake. Although difficult to analyze, the researchers estimated that there was a 10 % decrease in the risk for kidney stones in those who drank coffee and tea, a 60 % decrease in those who drank wine, and, surprisingly, a 44 percent increase in those who drank grapefruit juice.
A previous prospective study from these same researchers on men had also indicated an increased risk associated with the consumption of apple juice and grapefruit juice, and a decreased risk with the consumption of coffee, tea, and alcoholic beverages.
It is interesting to find out that different types of beverages are not alike in their ability to influence stone formation or prevention. However, it's certainly premature for doctors to make sweeping recommendations on the choice of beverage consumption in those who have had a kidney stone based on these preliminary studies. For the time being, though, it would seem prudent to recommend a decrease in the amount of fruit juice consumption in those who have already had a kidney stone, particularly a decrease in grapefruit juice.
Curham GC, Willett WC, et al. Beverage use and risk for kidney stones in women. Ann Int Med 128:534-540, 1998.