By David Kiefer, MD

Clinical Assistant Professor, Department of Family Medicine, University of Wisconsin; Clinical Assistant Professor of Medicine, Arizona Center for Integrative Medicine, University of Arizona, Tucson

Dr. Kiefer reports no financial relationships relevant to this field of study.

SYNOPSIS: Vitamin C supplementation decreases the risk of developing postoperative atrial fibrillation.

SOURCE: Shi R, Li ZH, Chen D, et al. Sole and combined vitamin C supplementation can prevent postoperative atrial fibrillation after cardiac surgery: A systematic review and meta-analysis of randomized controlled trials. Clin Cardiol 2018;41:871-878.

Vitamin C has many purported uses, to which the overwhelming number of articles on PubMed can attest. One interesting use, as per the recent systematic review detailed here, is for preventing postoperative atrial fibrillation. The authors mentioned an incidence ranging from 17-33%, with resulting complications, even though 80% of such patients return to sinus rhythm spontaneously. With a possible mechanism of oxidative stress, it would follow that an antioxidant, such as vitamin C, might play a role in preventing atrial fibrillation postoperatively.

Shi et al identified randomized, controlled (placebo or other control) trials in adults undergoing cardiac surgery, with vitamin C either as solo therapy or as adjunctive therapy. They reviewed 13 studies involving 1,956 patients. The primary outcome was the occurrence of postoperative atrial fibrillation; the pooled analysis revealed that vitamin C supplementation reduced the incidence of atrial fibrillation (relative risk, 0.68; 95% confidence interval, 0.54-0.87; P = 0.002), even more so when vitamin C was added to other therapies. Furthermore, secondary analyses revealed that vitamin C supplementation led to shorter stays in the ICU, less overall time in the hospital, and a reduced risk of adverse effects (not further specified other than advice that “high-dose intake of vitamin C should be avoided”).

The authors noted that there was a “moderate” amount of heterogeneity among the studies regarding methodology and a “moderate likelihood” of publication biases as per their statistical analyses, although the power of these tests was low because of the small number of studies involved. This systematic review nudges clinicians toward using vitamin C, either alone or in combination with typical cardiac medications, after cardiac surgery.

These recommendations are qualified slightly by the heterogeneity and risk of publication bias. This is not unheard of for systematic reviews, and possibly not a “real” issue given the small number of studies included and its effect on the power of the statistical methodology. Furthermore, an article of this type does not tell us how to use vitamin C; that is, in what dose or for how long. To answer those practical questions, it is necessary to look to the individual studies, where there were several approaches, including a range (1,000-2,000 mg) of oral or intravenous doses beginning one to two days before surgery and continuing for four to five days postoperatively.