CHICAGO — After tracking half a million adults aged 50 to 71 over a 10-year period, researchers have concluded that individuals who consume large quantities of red meat or processed meats have an elevated risk of mortality.
The study, "Meat Intake and Mortality," was published in the March 23 issue of Archives of Internal Medicine. The study was written by a team of researchers led by Rashmi Sinha, senior investigator, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, Md.
The study population included the N.I.H.—AARP Diet and Health Study Cohort of half a million people. Meat intake was estimated from a food frequency questionnaire administered at baseline.
The prospective study investigated red, white and processed meat intakes as risk factors for death, including from cancer and cardiovascular disease (C.V.D.). For the purposes of the study, red meat included all types of beef and pork. White meat included chicken, turkey and fish. Processed meat included bacon, sausage, luncheon meats, cold cuts, ham and hot dogs.
Participants in the study were recruited in 1995 from six states: California, Florida, Louisiana, New Jersey, North Carolina and Pennsylvania. In addition, subjects were recruited from Atlanta and Detroit.
During the 10 years, 47,976 males and 23,276 females died.
"There was an overall increased risk of total, cancer and C.V.D. (cardiovascular disease) mortality, as well as all other deaths in both men and women in the highest compared with the lowest quintile of processed meat intake," the researchers said. "In contrast, there was no association for processed meat intake and death from injuries and sudden death in either sex."
The researchers found an inverse association for total mortality and cancer mortality when comparing the highest with the lowest quintile of white meat intake.
In reaching their conclusions, the researchers had to sort through myriad confounding factors. Subjects who consumed more red meat were more likely to smoke, have a higher body mass index, have a higher daily intake of energy, total fat and saturated fat, and tended to have lower education and physical activity levels and lower fruit, vegetable, fiber and vitamin supplement intakes.
The researchers acknowledged that even adjusting for the confounding factors, "there is a possibility that some residual confounding by smoking may remain."
Mortality from cancer was 2,134 in the quintile of subjects who consumed the most red meat and 1,348 in the quintile that ate the least.
Adjusting for the confounding factors, the researchers concluded that men who consumed the most red meat were 31% more likely to die for any cause, 22% more likely to die of cancer and 27% more likely to die of C.V.D. than those who ate the least. For women, the increased likelihood was 36%, 20% and 50%, respectively.
Seeking to explain their findings, the researchers said a number of different mechanisms may link meat to mortality.
"In relation to cancer, meat is a source of several multisite carcinogens, including heterocyclic amines and polycyclic aromatic hydrocarbons, which are both formed during high-temperature cooking of meat, as well as N-nitroso compounds," the researchers said. "Iron in red meat may increase oxidative damage and increase the formation of N-nitroso compounds.
"Furthermore, meat is a major source of saturated fat, which has been positively associated with breast and colorectal cancer. In relation to C.V.D., elevated blood pressure has been shown to be positively associated with higher intakes of red and processed meat, even though the mechanism is unclear, except that possibly meat may substitute for other beneficial foods such as grains, fruits, or vegetables.
"In general, those in the highest quintile of red meat intake tended to consume a slightly lower amount of white meant but a higher amount of processed meat compared with those in the lowest quintile."
Reacting to the findings, the American Meat Institute was unimpressed. The A.M.I. was especially critical of the study’s reliance on subjects’ self reporting about what they ate over the previous five years.
"This imprecise approach is like relying on consumers’ personal characterization of their driving habits in prior years in determining their likelihood of having an accident in the future," the association said.
James H. Hodges, A.M.I. executive vice-president, defended meat products are a suitable part of a healthy, balanced diet.
"Studies show they actually provide a sense of satisfaction and fullness that can help with weight control," he said. "Proper body weight contributes to good health overall. Meat is an excellent source of zinc, iron, B12 and other essential vitamins and minerals."