In the present study, it was found that vitamin C deficiency and insufficiency was a great problem in our dialysis patients. The results showed that lower plasma vitamin C level was associated with lower prealbumin and higher hsCRP concentration both in MHD and in CAPD patients. These findings collectively suggest that vitamin C deficiency could be associated with the higher clinical inflammatory status in our patients.
Patients with active autoimmune disease, malignancy, hepatitis and acute infection were excluded, because these kinds of conditions could cause acute oxidative stress and acute change of hsCRP and vitamin C. Patients with stable cardiovascular disease, using central venous catheter, or on regular medication of ACEI, ARB or statins were not excluded, because we thought these conditions could not change the relationship between hsCRP and vitamin C.
We found in both MHD and CAPD groups plasma vitamin C level was inversely associated with age, patients with plasma vitamin C < 2 ug/ml(group A) had older age. And we also found higher hsCRP, lower albumin and lower prealbumin in such patients, in common with the results of some previous studies.[25,26] These results may due to a decreasing intake, and an increasing oxidative stress with ageing.[28–30]
Numerous studies reported that low plasma level of vitamin C in dialysis patients is commonly found owing to loss during dialysis procedure, inadequate dietary intake, reduced tubular reabsorption and impaired metabolism,[3,7,31–33] which was in consistent with our investigation.
Several clinical studies suggested a linkage between oxidative stress and inflammation in uremic individuals, but few had focused on the relationship between vitamin C status and inflammatory indicators, and, if analyzed, statistical relationship between vitamin C and each of hsCRP and prealbumin were not obtained in those previous investigations.[4,34,35] What we revealed in our study did not parallel these observations. One important reason is that most of the previous study patients had daily oral vitamin C supplementation during those investigations, which could change the inflammatory status. Second, differences in age, smoking status, dialysis vintage and proportion of diabetes in the study populations may be responsible for the different results.
We proposed that the association between vitamin C and inflammation markers observed in our study was explained by that inflammation and oxidative stress have certain internal relations. The oxidative products such as superoxide anion (O2−) and hydrogen peroxide (H2O2) during dialysis procedure could trigger inflammation in uremic patients. On the contrary, oxidative stress may be further aggravated by inflammation through potentiating respiratory burst activation in monocytes and neutrophils. Some investigations proved that hsCRP had a close correlation with thiobarbituric acid reactive substances(TBARS), a marker of lipid peroxidation, and α-tocopherol, and inflammatory proteins comprised C-reactive protein, fibrinogen and α1-antitrypsin were significantly correlated with most markers of oxidative stress. Jenny M et al found that acute administration of vitamin C reduced oxidant stress levels and improved NO-mediated resistance vessel dilatation in renal failure. Kamgar M at al also showed that MHD patients had a decrease trend in C-reactive protein compared with the baseline after given oral vitamin C supplement for 8 weeks although it did not get statistical significance. However, Fumeron C et al in a small-scale prospective study included 33 MHD patients (19 patients with oral vitamin C 250 mg three times per week after dialysis sessions, 14 patients without oral vitamin C) did not reveal that vitamin C could ameliorate oxidative stress and inflammation within 2 months.
Prealbumin is a negative acute-phase protein synthesized primarily by the liver, its plasma level reflects the presence of an ongoing or resolving inflammatory condition just as well as C-reactive protein. Prealbumin serum concentrations may have parallel changes with protein and energy intakes and inverse changes in inflammation, it was somewhat equally considered as both markers of nutritional status and inflammation. Mehdi Rambod et al reported in a 798 MHD patients cohort study, prealbumin inversely correlated with hsCRP and Interleukin-6 (IL-6), the surrogates of inflammation, which is very much like our observations.
Lee EJ et al reported that plasma vitamin C levels positively related to albumin with Serum ascorbic acid < or = 9 mg/L. In the present investigation, we also found plasma vitamin C positively related with albumin in Spearman correlation analysis, but the association did not exist after adjustment for sex, age, diabetes, mode of dialysis and other confounding effects. Several recent documents investigated that plasma vitamin C levels closely associated with hemoglobin, iPTH and alkaline phosphatase. However, we did not get such findings in both univariate and multivariate analysis in our sample, which maybe partly explained by the different selective standard of study population.
Previous study demonstrated that the elimination of plasma vitamin C is similar in both conventional hemodialysis and on-line hemodiafiltration, which is in line with our findings. In our study, there was no difference in plasma vitamin C level among the three MHD modalities. These results may be due to its small molecule (176.1 Da), highly soluble characteristic in water and low protein-bound. Patients receiving HDF treatment had lower log10hsCRP value compared with patients receiving HD treatment in our investigation, this observation was in consistent with some other previous results.[45,46]
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Cite this: Low Levels of Vitamin C in Dialysis Patients is Associated With Decreased Prealbumin and Increased C-reactive Protein - Medscape - May 01, 2011.