Of Meat and Mortality – Part 3: A China Study
Part 3 of Meat and Mortality is a review of a study from China. Not “The China Study”, but “a China study.”
If you read Part 2: NHANES when it first came out, I have updated it as of April 10 2013, to reflect that the meat intake categories were times per month not per week (only partially my fault as they listed them as “per week” in Table 2) and some further analysis making a strong argument that there was reverse causation in which people with prior disease had changed their red meat intake habits before the study began.
Now, on to Part 3: A China Study –
This prospective cohort study included 73,162 women taking part in the Shanghai Women’s Health Study and 61,128 men from the Shanghai Men’s Health Study. These numbers make it much larger than NHANES and only about 1/4 as large as EPIC.
The meat intake groups were divided into fifths, with the lowest category eating 17 g for women and 21 g for men (less than 1 oz) and the highest category eating 103 g (3.6 oz) for women and 126 g (4.4 oz) for men. The highest red meat intake categories were even less than what was seen in EPIC.
The authors summarize the results:
“[W]e found that red meat intake was positively associated with total mortality among men, but not among women. This discrepant association was also observed for lung cancer mortality. Further, red meat intake was positively associated with the risk of ischemic heart disease mortality, which was statistically significant among men. In contrast, red meat intake was inversely associated with the risk of hemorrhagic stroke mortality, which was statistically significant among women. Among men, the positive association between red meat intake and total mortality was significant in the low-income group, but no association was observed in the high-income group….”
The finding that red meat prevents hemorrhagic stroke (caused by bleeding in the brain) is not surprising, as higher rates of hemorrhagic stroke have consistently been found with low cholesterol levels. The thinking has always been that the risk of dying of a high-cholesterol-related diseases is so much greater than the risk of dying of hemorrhagic stroke that you’re better off with low cholesterol levels.
No statistically significant associations were found for poultry intake.
In addition to adjusting for the typical variables (age, smoking, alcohol, fruit and vegetable intake, etc), they adjusted the results for total caloric intake and a comorbidity index, thus raising the possiiblity that they wiped out any effect red meat might have had on mortality due to causing a higher caloric intake or previous disease.
The reason for the difference between the men and women might be that a much higher percentage of men than women smoke in China, 70% vs. 3%, which could cause confounding despite the attempt to adjust for smoking. The authors also thought that perhaps iron-deficiency in the women protected them from iron overload that could be caused by red meat.
The Chinese eat very little processed meat and the red meat they eat comes mostly from pigs (very few cows). I’m not sure if this matters, but thought it worth noting.
In summary, it’s too bad that these studies do not start out with a healthy population and do not provide a model not adjusted for conditions that red meat might effect.
Part 4 coming up…
1. Takata Y, Shu X-O, Gao Y-T, Li H, Zhang X, et al.Red Meat and Poultry Intakes and Risk of Total and Cause-Specific Mortality: Results from Cohort Studies of Chinese Adults in Shanghai. PLoS ONE. 2013 Feb 18;8(2):e56963. doi:10.1371/journal.pone.0056963 | link