Correspondence

Fluid Intake and Bladder Cancer

N Engl J Med 1999; 341:847-848September 9, 1999

Article

To the Editor:

Michaud et al. (May 6 issue)1 conclude that a high fluid intake is associated with a decreased risk of bladder cancer in men. An alternative explanation for the finding is that a high fluid intake results in decreased detection of bladder cancer.

Bladder cancer typically presents as gross or microscopic hematuria.2 Hematuria is detected by dipstick of urine or by microscopical examination of centrifuged urinary sediment. If urine is dilute, the chance of detecting hematuria decreases. Because the reported fluid intake correlated positively with urine volume in this cohort,3 study subjects in the fifth quintile of fluid intake (>2531 ml per day) would have been expected to have had more dilute urine than those in the first quintile of fluid intake (<1290 ml per day). The fact that urine was about twice as dilute in subjects in the fifth as compared with the first quintile may explain why the incidence of bladder cancer in the fifth quintile was about half that in the first quintile (33 cases in 91,675 person-years of follow-up vs. 61 cases in 89,415 person-years of follow-up).

Does an increase in fluid intake actually decrease the risk or merely obscure the diagnosis of bladder cancer?

Mark R. Goldstein, M.D.
466 Crescent Dr., West Chester, PA 19382

3 References

1. 1

   Michaud DS, Spiegelman D, Clinton SK, et al. Fluid intake and the risk of bladder cancer in men. N Engl J Med 1999;340:1390-1397
   Full Text | Web of Science | Medline

2. 2

   Shapiro CL, Garnick MB, Kantoff PW. Tumors of the kidney, ureter, and bladder. In: Bennett JC, Plum F, eds. Cecil textbook of medicine. 20th ed. Vol. 1. Philadelphia: W.B. Saunders, 1996:623-6.
   

3. 3

   Curhan GC, Willett WC, Rimm EB, Spiegelman D, Stampfer MJ. Prospective study of beverage use and the risk of kidney stones. Am J Epidemiol 1996;143:240-247
   Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: Dr. Goldstein raises the interesting point that an increase in fluid intake and excretion may obscure the diagnosis of bladder cancer by reducing the sensitivity of urinalysis or observation for the detection of hematuria. We feel that this possibility has little effect on the results of our study.

Most studies suggest that gross hematuria, detected by the patient, is usually the presenting sign of bladder cancer.1 Even diluting the urine many times, as occurs in modern toilet bowls, will usually not obscure the presence of gross hematuria. A minority of bladder cancers are initially detected by finding microscopic hematuria in a routine urinalysis. We agree that in a small number of cases, dilution of a sample may limit the detection of red cells in the urine. But even in these cases the progression of a superficial or invasive tumor would soon produce episodes of severe hematuria or other symptoms that would lead to the diagnosis. Because the follow-up period in our study was more than 10 years, it is unlikely that a brief delay in diagnosis would affect the overall results.

Finally, if dilution of urine substantially delays the diagnosis, we would expect many bladder cancers diagnosed in patients with higher fluid consumption to be at advanced stages. However, we found that men in the highest quintile of fluid intake had proportionally fewer cancers diagnosed at advanced stages (15 percent) than did those in the lowest quintile (26 percent).

Dominique S. Michaud, Sc.D.
Edward L. Giovannucci, M.D., Sc.D.
Harvard School of Public Health, Boston, MA 02115

Steven K. Clinton, M.D., Ph.D.
Arthur G. James Cancer Hospital and Research Institute, Columbus, OH 43210

1 References

1. 1

   Kantoff PW, Zietman AL, Wishnow K. Bladder cancer. In: Holland JF, Frei E III, Bast RC Jr, Kufe DW, Morton DL, Weichselbaum RR, eds. Cancer medicine. 4th ed. Vol. 2. Baltimore: Williams & Wilkins, 1997:2105-23.