NEW YORK (Reuters Life!) - Red meat is back under the spotlight as a possible cause of cancer with a US study finding the chemicals that paint hot dogs pink and preserve cold cuts could also raise the risk of bladder cancer.

Researchers led by Dr Amanda Cross of the National Cancer Institute point a tentative finger at nitrites and nitrates — compounds added to meat for preservation, color and flavour — but note that more research is needed to confirm the blame.

They said 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.

"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," Cross told Reuters Health.

For the study, Cross and her colleagues used information from a 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 seven-year study, a total of 854 participants (less than 0.3 percent) were diagnosed with bladder cancer.

The team researchers found 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 than people in the bottom fifth for consumption of these compounds.

The study, published in the journal Cancer (http://link.reuters.com/kem82n), also found that people who ate the most red meat tended to be younger, less educated, less active and have lower intake of fruit and vegetables and vitamins C and E than people eating the least red meat.

Each year, about 70,000 Americans are diagnosed with bladder cancer, and more than two 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, Cross told Reuters Health.

"However, other exposures are likely involved," she added.

She said while these findings are not conclusive and can't lead to any direct health advice, meat intake is thought to be a risk factor for other cancers.

She pointed 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)."