Based on findings from more than 300,000 people, the researchers point a tentative finger at nitrites and nitrates, compounds added to meat for preservation, color and flavor. But they note that more research is needed to confirm the blame.
Each year, about 70,000 Americans are diagnosed with bladder cancer, and more than 2 percent of the population will eventually develop the disease during their lifetime.
Several risk factors, including smoking and exposure to arsenic, have already been linked with the cancer, senior researcher Dr. Amanda Cross of the National Cancer Institute in Rockville, Maryland, told Reuters Health in an email.
“However, other exposures are likely involved,” she added. “We investigated whether compounds found in meat, formed either during the meat cooking process — heterocyclic amines or polycyclic aromatic hydrocarbons — or during meat preservation — nitrates and nitrites — were associated with bladder cancer.”
For the study, Cross and her colleagues used information from a National Institutes of Health-AARP study begun in 1995, which followed 300,933 older men and women from across the United States.
Participants filled out questionnaires on the meat they consumed, as well as how it was prepared and cooked. The researchers then matched this data to laboratory-measured meat components.
During the 7-year study, a total of 854 participants (less than 0.3 percent) were diagnosed with bladder cancer.
The team found that the top fifth of participants in terms of processed red meat consumption had about a 30 percent greater risk of being diagnosed with bladder cancer than those whose consumption ranked in the bottom fifth.
Further, people whose diets included the most nitrites (from all sources, not just meat) and those whose diets had the largest amount of nitrate plus nitrite from processed meats, were also nearly a third more likely to develop bladder cancer compared to people categorized in the bottom fifth for consumption of these compounds, the researchers report in the journal Cancer.
No significant effects were found for total red, white or processed meat consumption. Similarly, no link was made between bladder cancer and the consumption of heterocyclic amines, polycyclic aromatic hydrocarbons, or total nitrites or nitrates from processed meat.
During the cooking process, nitrites and nitrates combine with other chemicals that are naturally present in meat to form potentially cancer-causing N-nitroso compounds, which may then be excreted through the urinary tract where they can contact the lining of the bladder.
Animal studies have suggested that N-nitroso compounds are associated with bladder cancer, but there has been limited evidence of their effects on humans. In general, studies linking meat and bladder cancer have been inconsistent.
While these findings are not conclusive and can’t lead to any direct health advice, noted Cross, meat intake is thought to be a risk factor for other cancers. She points to a 2007 World Cancer Research Fund and American Institute for Cancer Research report, which concluded that individuals should “limit consumption of red meats (such as beef, pork and lamb) and avoid processed meat (ham, bacon, salami).”
SOURCE: reuters.com