Oral vitamin C supplementation decreased low-density lipoprotein in adults on hemodialysis: A systematic review and meta-analysis.

Plasma concentration of vitamin C tends to be lower in hemodialysis (HD) patients. Factors that could contribute to this include losses during dialysis and insufficient intake of vitamin C. Furthermore, vitamin C deficiency in HD patients may be related to inflammatory state, oxidative stress, endothelial dysfunction, and cardiovascular disease. We hypothesized that oral vitamin C supplementation improves lipid profile and diminishes inflammation and oxidative stress. Randomized clinical trials (RCTs) and nonrandomized studies (NRS) were analyzed, retrieved from EMBASE, PubMed, Scopus, and Web of Science databases (July 2024). Inclusion criteria: patients (>18 years) on HD; exclusion: intravenous supplementation, animals, children, adolescents, pregnant, lactating, hospitalized, transplanted. The Risk of Bias in Non-randomized Studies of Interventions and Risk of Bias 2 assessed risk of bias. Twelve studies were included (8 RCTs, 4 NRS), involving 549 participants (353 in the vitamin C supplementation, 97 control, 99 placebo). The lipid profile was evaluated in 6. The intervention ranged from 4 to 52 weeks, with doses from 51.4 to 1000 mg/day, orally. Three of 8 RCTs showed high risk of bias and 3 reported some concerns regarding the blinding process. The NRS presented low risk of bias. It was not possible to evaluate inflammation and oxidative stress because of differences in the variables. Meta-analysis showed a reduction in low-density lipoprotein (weighted mean difference: -24.81; I² 79.1%, confidence interval -44.28 to -5.33, P = .008), dose of 107.1-1000 mg/day, for at least 12 weeks. Limitations include the number of studies and patients, and the lack of knowledge about the intake and concentration of vitamin C. Vitamin C supplementation requires further clarification in HD patients.