Tuesday March 13 2012
Red meat was linked to cancer and heart deaths say researchers
“Small quantities of processed meat such as bacon, sausages or salami can increase the likelihood of dying early by a fifth,” The Daily Telegraph reported today.
The news is based on a large study that looked at the diets and health of over 120,000 people over periods of up to 28 years, assessing their diets every four years and following the development of any heart problems or cancer.
Researchers found that regularly eating red meat, in particular processed meat, was associated with a significantly higher risk of dying prematurely. Each 85 gram daily serving of unprocessed red meat (equivalent to about three thin slices of roast beef) was associated with a 13% increase in death risk during the study period, while one daily serving of processed meat (one hot dog or two slices of bacon) was associated with a 20% increased risk.
The researchers then input their data into a theoretical model, which estimated that 9.3% of early deaths in men and 7.6% in women in the study could have been prevented if all the participants had consumed fewer than 0.5 servings a day (about 42 gram a day) of red meat.
This was a well-conducted study but it could not conclusively prove that red meat raises the risk of premature death, although the results are of key interest and the evidence is mounting on the issue. According to UK dietary surveys, 4 in 10 men and 1 in 10 women eat more than 90 grams of red and processed meat a day. The Department of Health recommends that people eating more than 90 grams of red and processed meat a day limit their intake to no more than 70 grams a day in cooked weight. That is about the size of a large beefburger.
Where did the story come from?
The study was carried out by researchers from a number of research institutions, including the Harvard School of Public Health in the US. It was funded by the US National Institutes of Health, and the US National Heart, Lung and Blood Institute.
The study was published in the peer-reviewed medical journal, Archives of Internal Medicine.
This research was widely reported in the media, with several reports including comments from independent experts. The Daily Mail also included some critical comments on the research from the industry funded Meat Advisory Panel. The Sun’s claim that red meat kills was misleading.
What kind of research was this?
This was a prospective cohort study to investigate the association between red meat intake and early death in two large groups of men and women. It looked at both deaths from all causes and deaths from heart disease and cancer.
The researchers point out that red meat consumption has been associated with increased risk of chronic diseases but its association with the risk of mortality (death) remains uncertain.
What did the research involve?
The researchers analysed data from two large US cohort studies of health and lifestyle that took place in the US between 1976 and 2008. One of these studies examined outcomes in a range of healthcare professionals and the other only in nurses. In these studies, health questionnaires were sent to participants every two years to collect health-related information, with food questionnaires sent out every four years.
For the present analysis, researchers assessed the diets of 37,698 men and 83,644 women who were free of both cancer and heart disease at the start of the studies (1986 and 1980 respectively).
Diet was assessed using the validated food frequency questionnaires they had completed, which included detailed questions on both processed and unprocessed meat consumption.
In each questionnaire, participants were asked how often on average they consumed each food of a standard portion size, with nine possible responses ranging from ‘never, or less than once a month’ to ‘six or more times a day’. The standard serving size was 85 grams (3oz) for unprocessed red meat. Processed red meat included bacon (two slices, 13g) hot dogs (one, 45 grams). The participants were sent these questionnaires every four years until 2006.
The researchers collected information about deaths among participants by reports from next of kin, through postal authorities and by searching a national death index. The cause of death was primarily taken from medical records and death certificates. The researchers used codes from an international classification of diseases to distinguish between deaths due to cancer and cardiovascular disease.
They used appropriate statistical methods to analyse the data, taking account of possible other factors such as bodyweight, smoking status, physical activity level, family history, blood pressure and cholesterol.
In a further analysis the researchers modelled how death rates would be affected if one daily serving of red meat was substituted with an alternative food such as fish, poultry, nuts, legumes, low fat dairy or wholegrain.
What were the basic results?
The 121,342 participants were followed up for up to 28 years, during which time there were 23,926 deaths, including 9,464 deaths due to cancer and 5,910 from heart disease and stroke (collectively classed as cardiovascular disease [CVD]).
The researchers compared the highest consumers of red meat with the lowest consumers of red meat to calculate the increases in risk due to each additional serving a day. This was an average across all groups and it is worth noting that even the people with the lowest consumption of red meat were still eating, on average, a quarter of a serving a day and so were not vegetarian. The researchers found:
- consuming one serving of unprocessed red meat a day was associated with a 13% increased risk of early death (95% confidence interval [CI], 1.07-1.20), an 18% increase in risk of death from CVD (1.13-1.23) and a 10% increase in the risk of death from cancer (1.06-1.14)
- one serving of processed meat daily was associated with a 20% increased risk of early death (CI 95% 1.15-1.24), 21% increase in risk of death from CVD (1.13-1.31) and a 16% increase in the risk of death from cancer (1.09-1.23)
When the researchers modelled the impact of replacing meat with other foods their model estimated that:
- substituting one serving of red meat a day with one serving a day of other foods was associated with between 7% and 19% lower mortality risk
- 9.3% of early deaths in men and 7.6% in women taking part in the study could be prevented at the end of follow-up if all the individuals consumed fewer than 0.5 servings a day (approximately 42g a day) of red meat
How did the researchers interpret the results?
They say their study provides evidence that regular consumption of red meat, especially processed meat, is associated with an increased risk of death due to any cause, as well as due to CVD and cancer. Conversely, substitution with other protein sources is associated with a lower risk.
The authors propose that presence of saturated fat and iron in red meat might partly explain this association with higher risk of CVD, while the presence of other constituents such as sodium and nitrites might explain the additional risk associated with processed meats. They also point out that some of the compounds in red meat created by high temperature cooking are potential carcinogens.
This study had several strengths including its size, long follow-up period and detailed and repeated assessments of people’s meat intake. It also adjusted the results for other factors that might affect risk of mortality. However, relying on participants to self-report factors, such as their meat intake through questionnaires, introduces the possibility of error, although the questionnaires were validated. Furthermore, participants were mainly white health professionals, so the results may not be relatable to other populations.
This study cannot prove that regular consumption of red meat ‘kills’, as The Sun put it. Red meat is a good source of protein and certain nutrients such as iron, some vitamins and zinc, but it is already recognised that it is likely to raise the risk of cancer especially bowel cancer. The Department of Health advises adults who eat high levels of red and processed meat should reduce their intake to no more than 70 gram a day to reduce this risk. For advice on how to cut down, see our guidelines on red meat consumption.