Objective: To investigate whether reduced circulating levels of ascorbic acid in patients with systemic sclerosis (SSc) are a result of malabsorption.
Methods: Eight patients with SSc, but with no evidence of bacterial overgrowth, and 8 healthy controls were recruited. On the first day of study, each subject was given orally an aliquot of [14C] ascorbic acid, which was then "flushed out" by oral intake of unlabeled ascorbic acid for the following 7 days. Plasma samples were collected at specified intervals and urine was collected continuously over the 8 day study period. [14C] content of plasma and urine were measured by scintillation counting. For each subject, a plasma [14C] decay curve was drawn. Each subject's ascorbic acid absorption was assessed using the area under the curve (AUC) and the apparent renal clearance (CLr[app]). Ascorbic acid intake was assessed using dietary history and food composition tables.
Results: There were no differences in the dietary intake of vitamin C (p = 0.16) and body mass indices (p = 0.91) between patients and controls. The plasma [14C] AUC and CLr(app) were similar between patients and controls [AUC patient mean (standard deviation, SD) = 37.1 (6.8), AUC control mean (SD) = 38.6 (9.9), p = 0.74; CLr(app) patient mean (SD) = 0.57 (0.24), CLr(app) control mean (SD) = 0.47 (0.27), p = 0.45].
Conclusion: There was no evidence of impaired absorption of ascorbic acid in patients with SSc without bacterial overgrowth compared to healthy controls.