Zinc metabolism in rheumatoid arthritis: plasma and urinary zinc and relationship to disease activity

To study zinc absorption in patients with active rheumatoid arthritis (RA).

We studied zinc tolerance tests and 24 hour urinary zinc excretion before and after ingestion of 50 mg elemental zinc in 8 healthy volunteers (Group 1) and 13 patients with low RA activity (Group 2) and 16 patients with high RA activity (Group 3).

In Group 1, plasma zinc rose from 111 +/- 7 micrograms/dl to a peak of 200 +/- 24 micrograms/dl (mean +/- SEM) in 2 h. In Groups 2 and 3, plasma zinc before zinc ingestion was significantly lower than that of the control group (p < 0.00001 for both groups) and showed no significant increase in plasma after ingestion. Twenty-four hour urinary zinc excretions before and after zinc ingestion were significantly lower (p < 0.01, p < 0.0001 for Group 2; p < 0.05, p < 0.01 for Group 3, respectively) than those in the control group.

These results are compatible with zinc malabsorption and consequent zinc deficiency in patients with RA. Whether zinc deficiency contributes to perpetuation of disease activity by compromising cellular immune function needs further investigation.