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Diet and bladder cancer

 

Bladder cancer is the fourth most common cancer in men and the seventh most common cancer in women. In 1996 more than 300,000 new cases were diagnosed worldwide. Despite a relatively large number of studies investigating the role of diet in this illness, there is little agreement between them. This meta-analysis assesses the association between six aspects of diet (specifically fruit, vegetables, fat, meat, retinol, beta-carotene) and cancer of the bladder.

Message

A diet high in fruit and vegetables and low in fat will reduce the risk of bladder cancer.

Reference

CM Steinmaus et al. Diet and bladder cancer: a meta-analysis of six dietary variables. American Journal of Epidemiology 2000 151: 693-702.

Search

The literature was searched using MEDLINE and CancerLit. References of review articles were also examined. Case-control and cohort studies that presented their results in terms of a relative risk were included. Several studies were excluded if, for example, vitamin A had been inadequately defined or participants' data had been analysed in an earlier paper. Whenever possible, relative risks adjusted for smoking were included in the analysis.

Thirty-eight articles were identified. Table 1 shows the number of studies and cases which contributed to each analysis, the study type (case-control or cohort) and how many adjusted for smoking. All but one study used food frequency questionnaires to assess diet.

Table 1. Summary of studies contributing to each analysis.

Number of studies

Case-control:cohort

Smoking adjusted

Number of cases

High fat: 8

7:01

7

2,570

High meat: 8

5:03

4

2,008

Low fruit: 10

6:04

8

2,208

Low vegetables: 12

9:03

8

2,966

Low beta-carotene: 11

9:02

All

2,724

Low retinol: 10

7:03

8

2,339

Results

Risk of bladder cancer increased by 37% with a high fat intake; by 40% with low fruit consumption and by 16% with diets low in vegetables. No associations were found between bladder cancer and diets high in meat, low in retinol or beta-carotene. Table 2 shows these results.

Table 2. Risk of bladder cancer associated with intake of six dietary variables.

Aspect of diet

Increased risk

RR (95% CIs)

Low fruit

40%

1.40 (1.08 to 1.83)

Low vegetables

16%

1.16 (1.01 to 1.34)

High fat

37%

1.37 (1.16 to 1.62)

High meat

-

1.08 (0.82 to 1.42)

Low retinol

-

1.01 (0.83 to 1.23)

Low beta-carotene

-

1.10 (0.93 to 1.30)

Comment

One of the advantages of this meta-analysis is that the majority of studies adjusted for smoking. However, 43 of the 59 relative risk estimates were from case-control studies which are subject to bias (e.g. participants are asked to recall dietary intake before their diagnosis). Nevertheless, this paper gives us another reason for making sure our diets are high in fruit and vegetables and low in fat.