Plasma zinc and copper concentrations in rheumatoid arthritis: influence of dietary factors and disease activity.

Forty patients with rheumatoid arthritis performed a thorough 7-d diet recording. The food diaries were analyzed together with clinical and laboratory data by means of stepwise multiple linear regression to clarify the effects of both diet and the inflammatory disorder on the plasma concentrations of zinc and copper. The patients' daily dietary intakes of zinc and copper (24.3 +/- 7.54 and 3.48 +/- 1.55 mg/MJ) were comparable to the corresponding intakes in the ordinary Finnish diet (24.0 and 3.68 mg/MJ). In multivariate analyses the best predictors of plasma trace elements were the measures of disease activity and not the dietary factors. As an exception to this, there was a strong correlation between plasma copper-copper intake ratio and zinc intake both in univariate (r = -0.638, P less than 0.001) and multivariate analysis. This suggests that zinc depresses copper absorption with intakes in normal, physiological ranges.