A chronic inflammatory disease of the immune system, rheumatoid arthritis (RA) has been linked to a combination of genetic and environmental factors.
Aspects of lifestyle may explain as much as 40 percent of the risk. Cigarette smoking has consistently been found to play a role in RA's development. The role of nutritional factors is less certain. Studies have suggested the protective benefits of eating fish, the dangers of drinking coffee, and a reduction in disease risk for women who enjoy alcohol in moderation. Such associations, however, are still wide open to debate and further research.
Recently, a team of British researchers found that a diet lacking in fruit, especially varieties high in vitamin C, increases the risk of inflammatory arthritis, a common early sign of RA, as much as three-fold. Building on this compelling finding, they set out to investigate the association of other dietary habits with the onset of RA. Their results, published in the December 2004 issue of Arthritis & Rheumatism, indicate a high level of red meat consumption as an independent risk factor for inflammatory arthritis.
Led by Professors Alan Silman and Deborah Symmons at the University of Manchester, the team drew its subjects from a large, established research sample--over 25,000 men and women between the ages of 45 and 75 enrolled in the European Prospective Investigation of Cancer in Norfolk, England. Within this population, 88 new patients with inflammatory arthritis, affecting at least two major joints, were identified.
Nearly 40 percent of these patients satisfied the American College of Rheumatology criteria for RA at baseline. The patients were then matched, for age, sex, and body mass index, with 176 controls. At the study's onset, each participant completed a detailed 7-day food diary, with advance instruction on measuring food portions to help them be as specific as possible in recording their intake. Each participant also supplied information on his or her past and present status as a smoker.
Patients were more likely to have been former smokers; only 35 percent of the patients had never smoked compared with 85 percent of the controls. In terms of dietary factors, patients and controls were similar in most areas, including intake of total calories, fat grams, and vitamin D, as well as coffee, tea, and alcohol consumption. Patients had a lower intake of vitamin C, although the association of this factor with disease risk was not as strong as it was in the team's previous study. The most striking difference between the two groups was directly related to red meat consumption. After adjusting for smoking and other possible dietary confounders, patients with the highest level of red meat consumption had a two-fold risk for the development of RA. Patients who consumed high levels of red meat combined with other meat products showed similar high risk levels. Interestingly, a higher level of protein intake from all dietary sources was also associated with an increased disease risk, while higher levels of dietary fats, including saturated fat, did not have an impact.
Routinely eating burgers and steak, however, may only influence people with a predisposition for RA. "It may be that the high collagen content of meat leads to collagen sensitization and consequent production of anticollagen antibodies, most likely in a subgroup of susceptible individuals," the authors note. "Meat consumption may be linked to either additives or even infectious agents, but, again, there is no evidence as to what might be important in relation to RA."
"A high level of red meat consumption may represent a novel risk factor for inflammatory arthritis or may act as a marker for a group of persons with an increased risk from other lifestyle causes," Dr. Pattison and colleagues conclude. "It is unclear whether the association is a causative one."