While bladder cancer and nitrate were not linked, there was an association with dietary nitrite. Those with the highest nitrite consumption had an increased risk compared with those with the lowest intake -- but again this finding did not reach the traditionally accepted level of statistical significance.
Still, Cross and colleagues said the findings "support the hypothesis of 'N-nitroso compounds' involvement in bladder carcinogenesis, as processed meat also provides amines and amides necessary for the endogenous formation of [these compounds]."
The researchers said the findings "provide modest support" for an increased risk of bladder cancer associated with nitrite plus nitrate and PhIP, but acknowledged that the study was limited by a lack of information on urination frequency and bladder infections and limited data on beverage intake.
The authors called for further research into different dietary sources of nitrate and nitrite to determine which may have the strongest association with bladder cancer.
"Additional research is needed to confirm our findings of a possible increased risk of bladder cancer with intake of red meat and especially for PhIP, as prospective investigations of meat-related mutagens and this malignancy are lacking," they added.
Kundu told MedPage Today that "a lot of work still needs to be done before we can say that red meats or processed meats should be cut out all together."