A recent study has found that consumption of red meat (lamb, pork, and beef) increased the risk of overall mortality as well as the risk of mortality from the following eight causes: cancer, heart disease, respiratory disease, stroke, diabetes, infections, kidney disease, and liver disease.
With increasing affluence, meat consumption has risen steadily in North America, Europe, and parts of Asia. Numerous studies have linked premature death with red meat and processed meat (includes sausages, bacon, ham, corned beef, beef jerky, hot dogs, canned meat, and meat-based sauces) intake. By contrast, the intake of white meat has been shown to be beneficial although some studies have disputed this claim. Notably, these studies did not distinguish between unprocessed and processed white meat, which could be significant as nitrites and nitrites are added to meat during processing. Nitrites and nitrates in processed meat have been shown to increase the risk of different types of cancer. Similarly, heme iron, present in all meat, but abundant in red meat, is known to be associated with cancer and cardiovascular disease. All three, heme, nitrates and nitrites, are abundant in processed red meat, but their individual contributions to increasing mortality risk have not been examined in previous studies.
A study, initiated by researchers at the US National Institutes of Health in 1995 and published in the BMJ last month, attempted to examine the effects of meat and the red meat and processed meat constituents, heme iron, nitrites and nitrates, on mortality. A total of 536,969 retired individuals (316,505 men and 220,464 women) in the age group of 50-71 years living in the states of California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania and the metropolitan areas of Atlanta and Detroit were enrolled in the study.
A diet history questionnaire was used to collect information about the dietary habits of the participants at the start of the study in 1995. Based on the amount of meat intake (red, unprocessed red, processed red, white, processed white, and unprocessed white) and the amount of heme iron, nitrite, and nitrate intake, the participants were divided into five groups for each of these categories. The participants were followed until death or until December 31, 2011, whichever was earlier. The participants were followed up for a median duration of 15.6 years. A total of 128,524 participants (84,848 men and 43,676 women) died during follow-up. The leading causes of mortality included cancer, heart disease, respiratory disease, and stroke.
The researchers then attempted to link dietary habits with cause of death. A number of other factors that could affect mortality, such as age, sex, ethnicity, smoking status, physical activity, fruit and vegetable intake, total energy intake, alcohol consumption, body mass index, medical history, socioeconomic status, marital status, and education, were taken into account when analyzing data.
The study found that overall mortality and mortality from the eight specific causes listed above increased as red meat intake increased across the five participant groups. Red meat intake was most strongly linked to death from chronic liver disease. Study participants placed in the highest white meat intake category had a 25% lower overall mortality risk compared to those whose intake was lowest. Unprocessed white meat intake was associated with a lower risk of death from all specific causes examined, barring Alzheimer’s disease. However, the mortality risk was not lowered significantly by processed white meat consumption. Substituting red meat with white meat, especially unprocessed white meat, lowered the risk of overall mortality and mortality from specific causes.
The intake of heme iron increased overall mortality and mortality from all specific causes except Alzheimer’s disease. Similarly, both nitrite and nitrate intake increased mortality from all causes barring Alzheimer’s disease; death from diabetes, respiratory disease, and kidney disease was strongly linked to these compounds. A significant proportion of the increased mortality risk with processed red meat intake could be ascribed to the presence of nitrate and heme iron.
The study highlights the association of nitrites, nitrates, and heme iron in meat with increased overall mortality risk and the nine specific causes of death that were examined. These compounds are pro-oxidants and are thought to mediate their harmful effects by inducing oxidative stress and inflammation. Oxidative damage has been implicated in the development of cardiovascular disease, cancer, and diabetes among others. Cooked red meat may also contain variable amounts of mutagenic compounds, such as heterocyclic amines and polycyclic aromatic hydrocarbons, which may increase the risk of cancer. Notably, the World Heath Organization recently classified processed meat as a carcinogen and red meat as a probable carcinogen. Overall, the study supports previous findings and suggests that substituting red meat, especially processed red meat, with unprocessed white meat may be beneficial.
Written By: Usha B. Nair, Ph.D.