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Background Studies in animals have shown that the frequency of urination is inversely associated with the level of potential carcinogens in the urothelium. In humans, an increase in total fluid intake may reduce contact time between carcinogens and urothelium by diluting urinary metabolites and increasing the frequency of voiding. The data on fluid intake in relation to the risk of bladder cancer are inconclusive.
Methods We examined the relation between total fluid intake and the risk of bladder cancer over a period of 10 years among 47,909 participants in the prospective Health Professionals Follow-up Study. There were 252 newly diagnosed cases of bladder cancer during the follow-up period. Information on total fluid intake was derived from the reported frequency of consumption of the 22 types of beverages on the food-frequency questionnaire, which was completed by each of the 47,909 participants who were free of cancer in 1986. Logistic-regression analyses were performed to adjust for known and suspected risk factors for bladder cancer.
Results Total daily fluid intake was inversely associated with the risk of bladder cancer; the multivariate relative risk was 0.51 (95 percent confidence interval, 0.32 to 0.80) for the highest quintile of total daily fluid intake (>2531 ml per day) as compared with the lowest quintile (<1290 ml per day). The consumption of water contributed to a lower risk (relative risk, 0.49 [95 percent confidence interval, 0.28 to 0.86] for
Conclusions A high fluid intake is associated with a decreased risk of bladder cancer in men.
1440 ml [6 cups] per day vs. <240 ml [1 cup] per day), as did the consumption of other fluids (relative risk, 0.63 [95 percent confidence interval, 0.39 to 0.99] for >1831 ml per day vs. <735 ml per day).
Specific types of beverages may have other influences on bladder cancer. Some of the numerous metabolites of coffee modulate the activity of metabolizing enzymes,5 and alcohol increases the risk of cancer at several sites outside the bladder.6,7 Both alcohol and coffee also have a diuretic effect mediated by alterations in the hormonal control of renal function.8 Fruit and vegetable juices may contain bioactive compounds that can modulate the response to carcinogens,9 and chlorinated byproducts formed during the purification of water for public consumption may be potential carcinogens.10
Most investigations, primarily case–control studies, have not indicated a relation between coffee or alcohol consumption and the risk of bladder cancer.11,12,13,14,15,16,17,18,19 Findings with respect to an association between total fluid intake and the risk of bladder cancer have been inconsistent.18,19,20,21,22,23,24,25,26,27 Several case–control studies have tended to support an association between an increased risk of bladder cancer and consumption of water from public sources.28,29,30,31 Such unsettled questions, and sparse prospective data, led us to examine the relation of the total intake of fluids and the types of beverages to the risk of bladder cancer.
Methods
Study Population
The Health Professionals Follow-up Study was initiated in 1986, when 51,529 male health professionals 40 through 75 years of age from all 50 states answered a detailed mailed questionnaire on diet and medical history. The men were predominantly white, although no exclusions were made on the basis of race. Every two years, follow-up questionnaires were mailed to all surviving members of the cohort (up to six times per follow-up cycle for nonrespondents) to update the data on medical conditions and exposures.
To form the cohort for the current analysis, we excluded 1596 men with implausibly high or low scores for total food intake (outside the range of 800 to 4200 kcal per day) or with 70 items left blank on the base-line dietary questionnaire and 18 men whose questionnaires were missing the date of birth. In addition, 2006 men with cancer (other than nonmelanoma skin cancer) diagnosed before 1986 were excluded, in part because these men may have changed their diets as a result of their disease. The remaining 47,909 men were eligible for follow-up. The follow-up rate for this cohort averaged 94 percent per follow-up cycle during the five biennial cycles between 1986 and 1996. Participants who failed to respond to a questionnaire during one follow-up cycle were not removed from the study and were included in the next mailing of the questionnaire (they could skip one questionnaire but answer the next). The National Death Index was used to determine the vital status of nonrespondents, and the remaining nonrespondents were assumed to be alive and at risk for bladder cancer.
Assessment of Diet and Beverage Intake
To assess dietary intake, we used a 131-item semiquantitative food-frequency questionnaire32,33 in 1986 and again in 1990 and 1994. The base-line dietary questionnaire was completed in 1986, and dietary information was updated in 1990 and 1994. The questionnaire assessed the average intake over the previous year and included questions on the consumption of 22 different beverages. For each man, we calculated nutrient intake by multiplying the frequency reported for the consumption of each food item by the nutrient content of the specified portion size. The data on food composition were primarily from the U.S. Department of Agriculture.34 We calculated the total fluid intake using the 22 beverage items on the food-frequency questionnaire. The information on frequency and serving size was combined to give each member a score in milliliters.
In a study of the reproducibility and validity of the questionnaire among 127 men from this cohort, the Pearson correlation coefficient for nutrient intake measured by two one-week dietary records and by a food-frequency questionnaire was 0.50 for total fluid intake (Feskanich D: personal communication) and ranged from 0.52 for the intake of water to 0.93 for the intake of coffee.35 These values are within the range of correlations typically found in dietary-validation studies.36 In addition, we previously reported a correlation of 0.59 between total fluid intake as reported in a food-frequency questionnaire and 24-hour urine volume for men in the same validation study.37 In this cohort, the alcohol intake reported on the food-frequency questionnaire correlated highly with the alcohol intake as measured by two one-week dietary records (r = 0.86).38
Assessment of Nondietary Factors
At base line, and every two years thereafter, the participants provided information on their state of residence, current smoking status, exercise habits, weight, height, and use of medication. The base-line questionnaire provided detailed information on past smoking habits, the amount of time since quitting, the average number of cigarettes smoked per day before 15 years of age and at the ages of 15 through 19, 20 through 29, 30 through 39, 40 through 49, 50 through 59, and 60 or more years. To control for smoking, we derived total pack-years of smoking, incorporating all past smoking experience. One pack-year is equivalent to having smoked one pack, or 20 cigarettes, per day over an entire year.
Ascertainment of Cases
On each questionnaire, participants indicated whether they had received a diagnosis of cancer, heart disease, or other medical conditions. We confirmed the self-reported diagnosis of bladder cancer by a review of medical records (in 84 percent of the cases) or by obtaining additional data from the cohort member or a surviving family member (16 percent). The end points in this study were cases of bladder cancer that were first diagnosed between February 1986 and January 31, 1996; there were 252 such cases. According to a review of pathology reports, more than 90 percent of the cases of bladder cancer were transitional-cell carcinomas.
Statistical Analysis
We computed person-time of follow-up for each participant from the return date of the 1986 questionnaire to the date of diagnosis of bladder cancer, death from any cause, or January 31, 1996, whichever came first. In the main analysis, categories of exposure were determined on the basis of the responses to the 1986 questionnaire, except for age and current smoking status, which were updated every two years in all analyses. Current smoking status was based on the questionnaires returned in 1986, 1988, 1990, 1992, and 1994. The incidence of bladder cancer for each category of fluid intake was calculated as the number of participants with bladder cancer divided by the person-time of follow-up. The relative risk was computed as the incidence among the participants in a category of fluid intake divided by the incidence in a specific reference category. Participants whose questionnaires were missing information for any specific beverages (less than 10 percent for any beverage) were assigned to the lowest category of intake for that beverage, because our cohort validation study indicated that, in most instances, the missing item was not consumed.
We used pooled logistic regression39 with two-year increments to adjust for age (in five-year categories), pack-years of smoking (six categories, including no history of smoking), current smoking status, geographic region, and total intake of fruits and vegetables (a potential risk factor40). Data on participants who died or received a diagnosis of bladder cancer during a two-year cycle were censored at the end of that two-year period and were not entered in any subsequent two-year cycles. With short intervals between questionnaires and low rates of events, this approach tends to give results very similar to those from a Cox regression model with time-dependent covariates.39 In addition, we included total energy intake in all multivariate models to reduce extraneous variation introduced by underreporting or overreporting on the food-frequency questionnaire.36
In a separate analysis, we examined the relation between total daily fluid intake and the incidence of bladder cancer by updating the base-line information on fluid intake with data on fluid intake from subsequent questionnaires (1990 and 1994). In these analyses, data on fluid intake from the 1986 questionnaire were used to allocate person-time to each of the quintiles of exposure between 1986 and 1990; the average of the fluid intakes from 1986 up to 1990 was used from 1990 up to 1994, and the average of 1986, 1990, and 1994 was used for subsequent years (1994 through 1996). Cumulative updating may reduce the effects of variations in the intake of individual participants and better represents long-term intake. We performed tests for trend by assigning the median value for each category and modeling this variable as a continuous variable, using pooled logistic regression for multivariate analyses. All reported P values are two-sided. Tests for interaction were performed with use of likelihood-ratio tests. In addition to the tests for trend described above, pooled logistic-regression models of the log relative risk of bladder cancer on the restricted cubic spline41 of beverage and total fluid intake were fitted to the data. When likelihood-ratio tests were used to test the hypothesis of a linear relation through a comparison of the spline models to linear models, none of the associations between specific beverages or total fluid intake and the risk of bladder cancer showed evidence of departure from linearity.
Results
A total of 252 cases of bladder cancer and 435,458 person-years were available for the main analyses. Age and smoking were both strongly associated with the risk of bladder cancer. Among men with a history of 65 or more pack-years of cigarette smoking, bladder cancer was 3.7 times as likely (95 percent confidence interval, 2.2 to 4.5) as among men who had never smoked. The relative risks of bladder cancer were 5.6, 6.2, and 11.6 for men 70 through 74, 75 through 79, and 80 or more years old, respectively, as compared with those younger than 50. The risk of bladder cancer was also higher (relative risk, 1.8; 95 percent confidence interval, 1.2 to 2.7) in the northeastern United States than in the West.
The distribution of established or potential risk factors, standardized for age, was examined according to total daily fluid intake (Table 1). Both the number of pack-years of smoking and the proportion of participants who were current smokers increased with higher levels of total fluid intake. The level of physical activity and the total number of servings of fruits and vegetables per day increased with higher quintiles of total fluid intake. Macronutrient intakes did not differ substantially among the levels of total fluid intake.
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To examine the possibility that an anticarcinogenic substance in a particular beverage, rather than fluid intake itself, accounted for our findings, we evaluated each specific type of beverage (Table 3). Apart from water, no beverage had a statistically significant association with the risk of bladder cancer, although all (except fruit juice) had inverse relations. We also created categories for the intake of individual beverages to examine extreme consumption levels in relation to the risk of bladder cancer (Table 4). The daily consumption of 1440 ml (6 or more cups) of water was associated with a substantial reduction (51 percent) in the risk of bladder cancer as compared with the risk among participants who consumed less than 240 ml (1 cup) per day (P for trend, = 0.001). Although none of the other individual beverages had a statistically significant association with the risk of bladder cancer, when we added water and all other fluids to a multivariate model simultaneously, the relative risk was 0.49 (95 percent confidence interval, 0.28 to 0.86) for water intake of 1440 ml or more per day as compared with less than 240 ml per day and 0.63 (95 percent confidence interval, 0.39 to 0.99) for the consumption of more than 1831 ml of other fluids per day as compared with less than 735 ml per day (data not shown).
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We investigated whether the relation between total fluid intake and the risk of bladder cancer was modified by cigarette smoking (Table 5). Because the numbers of cases for some of the strata were small, we collapsed total daily fluid intake into quartiles. The relative risk of bladder cancer for the highest as compared with the lowest quartile of total daily fluid intake was 0.31 among current smokers, 0.59 among former smokers, and 0.58 among those who had never smoked. There was no statistically significant interaction between smoking and total fluid intake (P=0.61 for current smokers vs. those who had never smoked; P=0.99 for former smokers vs. those who had never smoked).
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In this prospective study of 47,909 men, a high intake of fluids was associated with a reduced risk of bladder cancer after control for potential risk factors. When fluid intake was modeled as a continuous variable, the risk of bladder cancer decreased by 7 percent for every increment of 240 ml in daily fluid intake we measured. Study participants in the highest quintile of fluid intake had a 49 percent lower incidence of bladder cancer than those in the lowest quintile. The consumption of both water and all other types of fluid combined contributed to the lower risk.
In the only other cohort study of fluid intake, which involved 52 cases of bladder cancer, the total intake of fluid was not significantly associated with the risk of bladder cancer,18 although the statistical power of the study was low. A case–control study did report a significant inverse association between total fluid intake and bladder cancer in women, particularly among smokers.27 A number of case–control studies,20,21,22,23,24,31 but not all,19,25,26,27,42 have reported positive associations between the total intake of fluids and the risk of bladder cancer, explained largely by the intake of coffee or alcohol.21,22,23 In part, the positive findings for coffee and alcohol intake in some studies may be due to residual confounding resulting from incomplete control for the effect of cigarette smoking. The results of most studies, including ours, do not provide evidence that the intake of alcohol13,14,15,17,18 or coffee11 increases the risk of bladder cancer.
Because our base-line questionnaire did not assess the source of water consumed (tap water vs. bottled water), we were unable to determine the influence of the source of water on our results. However, according to a questionnaire filled out by 34 percent of the cohort in 1993 and 1994, 78 percent of the men usually drank municipal water, and of the bladder cancers in that subgroup, 75 percent of the cases developed in participants who drank municipal water. Moreover, an inverse association between water intake and the risk of bladder cancer was consistent among all regions of the United States and was apparent among the participants who were known to drink municipal water (48 cases; relative risk, 0.57; 95 percent confidence interval, 0.21 to 1.53 for highest vs. lowest quintile of total fluid intake). Previous investigators have hypothesized that chlorination byproducts may account for the increased risk of bladder cancer in some regions.10,28,29,30,31 However, establishing a person's exposure to chlorination byproducts is difficult. In studies that have examined persons with long-term exposure to chlorinated water (exposure lasting 40 or more years), the relative risk of bladder cancer, as compared with that among persons with no such exposure, has not exceeded 2.0.28,31,42 Although we cannot exclude the possibility that long-term exposure to chlorination byproducts in public water may increase the risk of bladder cancer, our data suggest that in the United States, a high intake of water may reduce the risk of bladder cancer by about 50 percent on average.
Many carcinogenic xenobiotics are ultimately metabolized to methylated or conjugated products, which increases their water-solubility and facilitates excretion. Although most conjugated substances are not highly reactive, certain urinary conditions can facilitate the conversion of inactive substances to their carcinogenic forms.43 Concentrated urine, or less-frequent micturition, will increase the exposure of the bladder urothelium to urinary carcinogens. This theory, named the urogenous-contact hypothesis, has been offered as an explanation for the inverse association found between the risk of bladder cancer and fluid intake.4,27 This hypothesis is supported by a study in which dogs that had been administered a known human urinary bladder carcinogen (4-aminobiphenyl) had significantly increased urothelial levels of DNA adducts when the average frequency of voiding was reduced.44 The relation of fluid intake to risk that we found in our study was at least as strong among smokers, who have a high concentration of tobacco-related carcinogens in the urine, as among nonsmokers. Because the underlying rate of cancer is three to five times as high among smokers as among nonsmokers, smokers stand to benefit most by increased fluid intake.
The removal of cases diagnosed during the first three or five years of this study did not alter the overall results; therefore, it is unlikely that the associations between total fluid intake and the risk of bladder cancer arose because of dietary changes made before diagnosis by men with latent tumors. Because dietary factors and known confounders were measured before bladder cancer was detected, it is unlikely that the findings were influenced substantially by recall or selection bias.
We cannot rule out the possibility that some unmeasured confounder accounted for the associations found in this study, but residual confounding by the covariates that we included is unlikely. In this cohort, the only strong risk factor for bladder cancer (with the exception of age) was smoking. The control for smoking accounted for virtually all the differences found between the age-adjusted and multivariate relative risks, including the stronger inverse relation of the multivariate risk to total fluid consumption. Additional controls for the amount of current cigarette smoking, and for time since quitting among former smokers, did not alter the results, and we found an inverse association between total fluid intake and the risk of bladder cancer among those who had never smoked. Therefore, residual confounding by smoking is unlikely to be responsible for our findings. Furthermore, we observed similar results when we fitted a Cox regression model with time-dependent covariates and age as the time scale to our data. For these reasons, residual confounding by either smoking or age is unlikely to explain the findings. We found almost no differences in the relative risk of bladder cancer calculated before and after we controlled for fruit and vegetable intake.
Additional studies are needed to evaluate the temporal relation between increased fluid consumption and changes in the risk of bladder cancer and to determine the generalizability of our results to other populations. In the meantime, a generous intake of fluids is sensible, because it can reduce the risk of kidney stones37,45 and possibly bladder cancer as well.
Supported by grants from the National Institutes of Health (CA 55075 and HL 35464) and the American Cancer Society (Special Institution Grant no. 18).
Source Information
From the Departments of Nutrition (D.S.M., E.B.R., W.C.W., E.L.G.), Epidemiology (D.S., E.B.R., W.C.W., E.L.G.), and Biostatistics (D.S.), Harvard School of Public Health, Boston; the Channing Laboratory, Department of Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston (E.B.R., G.C.C., W.C.W., E.L.G.); and the Arthur G. James Cancer Hospital and Research Institute, Ohio State University, Columbus (S.K.C.).
Address reprint requests to Dr. Michaud at the Department of Nutrition, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115 or at hpdsm{at}gauss.bwh.harvard.edu.
References
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Related Letters:
Fluid Intake and Bladder Cancer
Goldstein M. R., Michaud D. S., Giovannucci E. L., Clinton S. K.
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Full Text
N Engl J Med 1999;
341:847-848, Sep 9, 1999.
Correspondence
This article has been cited by other articles:
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