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Can Too Many Steaks Shorten Life, Hasten AMD?

A preponderance of observational data indicates that too much red meat is a risk factor for heart disease and cancer. The results of two new prospective studies support that idea, and suggest that excessive intake might impact visual health as well.

The first study, published in the Archives of Internal Medicine, reports that eating red and processed meat is associated with modest increases in total mortality, cancer mortality, and cardiovascular mortality rates (1). Red meat consumption was also positively linked with early AMD in another paper appearing in the American Journal of Epidemiology (2).

First Study Summary

The National Institutes of Health's AARP Diet and Health Study enrolled about half a million people aged 51-71, estimated their intake of meat using a food frequency questionnaire, and used Cox regression models to determine hazard ratios and confidence intervals within quintiles of meat intake. Red meat included all types of beef and pork, the white meat category included poultry and fish, and processed meat category contained both red and white meat in the form of cold cuts, hot dogs, bacon and sausage.

After 10 years of follow-up, red and processed meat raised the risk of CVD, cancer and total mortality in both men and women in the highest quintile of intake. In contrast, those with the highest white meat intake (and a lower red and processed meat diet) had a decreased risk in both total and cancer mortality.

Second Study Summary

To help clarify the role of red meat intake in AMD, approximately 5600 subjects aged 58-69 took part in the Melbourne Collaborative Cohort Study. The presence of AMD was determined by non-mydriatic retinal photography. There were 1680 cases of AMD, defined as the presence of drusen 63 µm or larger, with or without the presence of hyper / hypo-pigmentation. Cases of late AMD, indicated by the presence of choroidal neovascularization or geographic atrophy, numbered 77. Compared with eating red meat less than 4.5 times weekly, downing it 10 or more times a week raised the odds of having early AMD by 47%. Intake of chicken was not related to early AMD, but eating it at least 3.5 times weekly lowered the risk of late AMD.

While confirmatory data are needed, a high level of red meat consumption may be a novel risk factor for early AMD, according to the study's authors. They point out that high meat intake is associated with higher levels of N-nitroso compounds, heme iron, and advanced glycation end products, which could result in oxidative damage and ultimately be toxic to the retina.

The Clinician's Role as Public Health Advocate

An editorial accompanying the first study notes that too few clinicians speak out about the importance of dietary moderation. One useful tool to engage patients in healthful eating is the 2009 Mediterranean Diet Pyramid. Endorsed by the WHO and the Harvard School of Public Health, the Mediterranean style of eating is also a lower glycemic diet - a factor that may also be protective of retinal health (3).

Note: A colorful, 2009 updated poster of the Mediterranean Pyramid for display in medical practices is available from www.oldwayspt.org

References

1. Sinha R, et al. Meat intake and mortality: a prospective study of over half a million people. Am J Epidemiol 169:867-76, 2009.
2. Chong EW, et al. Red meat and chicken consumption and its association with age-related macular degeneration. Arch Intern Med 169:543-45, 562-71, 2009.
3. Chiu CJ, et al. Association between dietary glycemic index and ARMD in non-diabetic participants in the Age-Related Eye Disease Study. Am J Clin Nutr 86:180-8, 2007.