Friday, March 16, 2012

Red meat increases early mortality risk. At least if you live in the USA. Part 1

Background: This week, the news showed us that red meat consumption decreases lifespan (1, 2). But was this effect caused by the red meat, or because meat eaters had a generally unhealthy lifestyle?

The news reports based their conclusion on results from the "Health Professionals Follow up Study" and the "Nurses' Health Study" (3) by Pan et al. 37,698 men and 83,644 women participated in the research. At baseline, participants were asked to complete a food frequency questionnaire. And they were asked to do this again every 4 years. Until now, 8,926 men and 15,000 women died during follow-up (22 years for men and 28 years for women). Men in the highest quintile of red meat consumption had a 37% increased risk of dying within the follow-up period. And risk increased by 24% among women. Both mortality from cardiovascular disease and cancer increased significantly among both men and women. Both processed- and unprocessed red meat increased risk of early mortality.

What did the meat industry think of these results?
Not surprisingly, the American Meat Industry (AMI), criticized the results (4):
The American Meat Institute (AMI) said the study’s main flaw was the fact that it relied on self-reporting to survey participants' diets, but that the method of collecting data was also 'highly inaccurate'.
This conclusion automatically implies that all research on diet is nonsense. All research relies on self-reporting of dietary intakes, unless you are under 24-hour/day surveillance. Who else is going to report what you consume?

The AMI continuous:
According to AMI, the researchers inserted estimated data when actual survey measurement was missing, and stopped updating the dietary information as soon as participants reported a diagnosis.
According to Pan et al, missing values in a follow-up food frequency questionnaire were replaced with the cumulative averages before the missing values.
Additional analysis included updating a participant's diet even after he or she reported a diagnosis of major chronic disease. This can be seen in the online supplemental data (5). Risk of early mortality remained significantly elevated after this update.

According to the AMI:
Red and processed meat continues to be a healthy part of a balanced diet and  nutrition decisions should be based on the total body of evidence, not on single studies that include weak and inconsistent evidence and stand in contrast to other research and to the Dietary Guidelines for Americans, 2010.
No references are given to show that red and processed meat continue to be a healthy part of a balanced diet. No references are given to show that other studies found different results.
The statement is in contradiction to what the Pan et al actually found. Table 2 of the article shows that risk of early mortality increased with every quintile of consumption among both men and women (3). In addition, participants in the 2nd quintile of consumption had a significantly increased risk of dying, compared to participants in the 1st quintile of consumption. Showing that even moderate intakes might decrease lifespan.

Do consumers of red meat die early because of the meat, or because they live unhealthier lives?
Pan et al diminished the chance that possible confounders would influence the relation between red meat and mortality. They adjusted for age, body mass index, alcohol consumption, physical activity, smoking status and other factors. And for dietary variables which may be linked to a healthier lifestyle: whole grains, fruits, and vegetables. Additional adjustment for other foods (fish, poultry, nuts, beans, and dairy products) did not appreciably alter the results.

And according to the researchers:
In addition, the FFQs used in these studies were validated against multiple diet records. However, the measurement errors inherent in dietary assessments were inevitable, including misclassification of ham or cold cuts as unprocessed red meat and inaccurate assessment of red meat content in mixed dishes. Because of the prospective study design, any measurement errors of meat intake are independent of study outcome ascertainment and, therefore, are likely to attenuate the associations toward the null. In the sensitivity analysis accounting for measurement errors, the risk estimates became stronger.
All types of red meat increased risk of early mortality
Pan et al included 6 types of red meat:
-Beef, pork, or lamb as main dishes.
-Beef, pork, or lamb as a sandwich or mix dish.
-Hog dog.
-Other processed red meat.
Mortality rates significantly increased with higher intakes of all 6 types of red meat, among both men and women.

Results from 2 prospective studies show that both unprocessed- and processed red meat may increase risk of early mortality. Risk of death increased with every quintile of increasing consumption.
Evidence for a possible causal relation strengthens when findings are consistent. According to this criterion, red meat did not do well: Early mortality risk increased with all types of red meats examined. And both cardiovascular disease- and cancer mortality risk rose significantly. Findings were similar among men and women.

In Part 2, I will examine if other studies found similar effects.

1) Abcnews. Red meat tied to increased mortality risk. March 12, 2012.
2) Nytimes. Risks: more red meat, more mortality. March 12, 2012.
3) Pan A. Red meat consumption and mortality: results from 2 prospective cohort studies. Arch Intern Med. 2012 Mar 12. [Epub ahead of print].
4) Michel M. Study linking red meat to high mortality under fire. March 13, 2012.
5) Pan A. Red meat consumption and mortality: results from 2 prospective cohort studies. eTables & eFigure.


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