Too Much of a good thing?

  A question I forgot to add to my last posting was:
  Is drinking that much tea (two to three quarts a day) cause for
  Kidney Stone?  Should I stop drinking that much tea?
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Dear Hector,
Your question is very relevant in light of strong association between dietary oxalate consumption and incidence of calcium oxalate stone disease.  All types of tea have high oxalate content.  There is an ongoing concern that widespread consumption of large amounts of iced tea in the southeastern United States could be related to the high incidence of urolithiasis. Although dietary oxalate is responsible for only 10% to 15% of total urinary oxalate (Hodgkinson, 1977), excessive dietary intake may cross the threshold for stone disease. A case control study from Newfoundland examined tea consumption in stone formers but found no evidence to support the suggestion that tea drinking is a risk factor for calcium oxalate urolithiasis (Churchill et al., 1981). These investigators calculated that one cup of tea would add only 0.5 mg of oxalate to total urinary excretion.  This however will increase in proportion to the amount of consumption.
In fact, in a recent study, authors evaluated the relation between the intake of 21 different beverages and the risk of symptomatic kidney stones in a cohort of 45,289 men, 40-75 years of age, who had no history of kidney stones. Beverage use and other dietary information was measured by means of a semiquantitative food frequency questionnaire in 1986. During 6 years of follow-up (242,100 person-years), 753 incident cases of kidney stones were documented. After adjusting simultaneously for age, dietary intake of calcium, animal protein and potassium, thiazide use, geographic region, profession, and total fluid intake, consumption of specific beverages significantly added to the prediction of kidney stone risk (p < 0.001). After mutually adjusting for the intake of other beverages, the risk of stone formation decreased by the following amount for each 240-ml (8-oz) serving consumed daily: caffeinated coffee, 10%; decaffeinated coffee, 10%; tea, 14%; beer, 21%; and wine, 39%. For each 240-ml serving consumed daily, the risk of stone formation increased by 35% (4-75%) for apple juice and 37% (1-85%) for grapefruit juice (Am J Epidemiol 1996 Feb 1;143(3):240-7, Prospective study of beverage use and the risk of kidney stones. Curhan GC, Willett WC, Rimm EB, Spiegelman D, Stampfer MJ).
In another recent study same group studied this relationship in women. Authors performed a prospective cohort study with 8 years of follow-up in 81093 women who were 40 to 65 years of age in 1986 and had no history of kidney stones. Beverage use and diet were assessed in 1986 and 1990 with a validated, self-administered food-frequency questionnaire. During 553 081 person-years of follow-up over an 8-year period, 719 cases of kidney stones were documented. After risk factors other than fluid intake were controlled for, the relative risk for stone formation for women in the highest quintile of total fluid intake compared with women in the lowest quintile was 0.62 (95% CI, 0.48 to 0.80). Inclusion of consumption of specific beverages in the multivariate model significantly added to prediction of risk for kidney stones (P < 0.001). In a multivariate model that adjusted simultaneously for the 17 beverages and other possible risk factors, risk for stone formation decreased by the following amount for each 240-mL (8-oz) serving consumed daily: 10% for caffeinated coffee, 9%  for decaffeinated coffee, 8% for tea, and 59%  for wine. In contrast, a 44% increase in risk was seen for each 240-mL serving of grapefruit juice consumed daily (Ann Intern Med 1998 Apr 1;128(7):534-40. Beverage use and risk for kidney stones in women. Curhan GC, Willett WC, Speizer FE, Stampfer MJ).
There have been some additional studies which have suspected tea as a contributory factor towards the stone disease.  However final status is still not clear.  It may be safe to say that too much of any thing is bad.  Therefore you should cut down the ice tea consumption and replace it with other safe beverages.
This information is provided for general medical information purposes only. Please consult your physician for diagnostic and treatment options pertaining to your specific medical condition.
The Henry Ford Hospital has experience in the evaluation and treatment of problems such as you describes. They would be most interested in helping you. You can reach them through our toll-free number (1-800-653-6568). We can also arrange local accommodations through this number if this is your need.
Sincerely,
HFHS M.D.-A.T.
*keyword: urinary  calculi, oxalate ingestion