BOSTON, Massachusetts—Avoiding red meat may lower your cardiovascular risk but is not likely to protect you against rheumatoid arthritis (RA), according to the largest study to date of diet and RA. The prospective analysis of data from 82,063 women in the Nurses' Health Study using Cox proportional hazard models to calculate the rate ratio (RR) for an association between protein, meat, or iron intake and risk of RA was not confirmed.¹

Reporting in Arthritis Research & Therapy, lead author Elizabeth Benito-Garcia, MD, MPH, writes, "The multivariate models showed no association between RA and any measure of protein or iron intake. In comparisons of highest to lowest quintile of intakes, (RR = 1.17 for total protein [95% confidence interval (CI) 0.89-1.54; P for trend = 0.11] and RR = 1.04 for total iron (95% CI 0.77-141, P for trend = 0.82). Red meat, poultry, and fish were also not associated with RA risk." Dr. Benito-Garcia is with the division of rheumatology, immunology and allergy at Brigham and Women's Hospital, in Boston, and the BioEPI Clinical and Translational Research Center in Oeiras, Portugal.

Diet assessed at six points over nearly 20 years in over 82,000 women

The investigators assessed dietary intake at baseline in 1980 and five more times through 2002 in the 82,063 women in the study. Over this period, they also identified 546 incident cases of RA, confirmed by a connective tissue disease screening questionnaire and by medical records review.

The Cox analysis calculated the RR for an association between new-onset RA and protein intake (total, animal, vegetable) and/or iron (total, dietary, from supplements, and heme iron). The analysis adjusted for age, smoking, body mass index, and reproductive factors.

The Benito-Garcia study was inspired by suggestions that high-protein diets might contribute to RA and low-protein diets relieve it.

Pattison et al reported in 2004 a nested case-control study of patients who presented with new cases of inflammatory polyarthritis (not specifically RA) in the population-based European Prospective Investigation of Cancer in Norfolk (EPIC-Norfolk) study.² Study subjects' dietary intake had been assessed at baseline using a 7-day food diary.

The researchers found 88 new cases of inflammatory polyarthritis between 1993 and 2002 among 25,630 subjects. Each of these cases was matched with two controls for the risk factor analysis.

The arthritis patients had greater red meat intake than nonarthritic controls, and lower vitamin C intake. However, adjusting for total energy intake, smoking, and other possible dietary confounders weakened this association. In an accompanying editorial, Hyon K. Choi, DrPH, of Massachusetts General Hospital and Harvard Medical School, in Boston, pointed out that the association between red meat intake and risk of inflammatory polyarthritis was "statistically borderline" (RR = 1.9, 95% CI 0.9-4.0).³  Dr. Choi also noted possible confounding by fish intake, which typically is inversely associated with meat intake and which was not considered in the Pattison study.

"Dietary studies are very challenging, since a person's dietary intake day in/day out is very hard to measure accurately. Given the larger number of cases in the Benito-Garcia study, I would tend to trust it more, but it is not necessarily easy to determine which finding is correct," David Felson, MD, MPH, of the Boston University School of Medicine, in Massachusetts, told CIAOMed.

E-mail any comments to .

Reference

1. Benito-Garcia E, Feskanich D, Hu FB, et al. Protein, iron and meat consumption and risk of rheumatoid arthritis: a prospective cohort study. Arthritis Res Ther. 2007;9:R16 (doi:10/1186/ar2123)
2. Pattison DJ, Symmons DPM, Lunt M, et al. Dietary risk factors for the development of inflammatory polyarthritis. Arthritis Rheum. 2004;50:3804-3812.
3. Choi HK. Diet and rheumatoid arthritis: red meat and beyond. Arthritis Rheum. 2004;50:3745-3747.