This study was a double-blind, random allocated, placebo-controlled trial conducted at two companies in the Republic of Korea. Participants were recruited between March and April 2008. We randomly assigned 73 participants to the vitamin C group, and 74 participants to the placebo group. The participants received a single intravenous treatment of either vitamin C (10 g) or normal saline. The institutional review board of Dongguk University Ilsan Hospital approved the protocol, and all patients provided written informed consent. The clinical trial registration of this trial is ClinicalTrials.gov NCT00633581.
Setting and Participants
The study was designed to include 150 volunteers (Korean, office workers or salespeople). The subject size was estimated based on the results of a pilot study with the following parameters: type I error α = 0.05, power 1-β = 0.8, and dropout rate = 10%. The sample variance of the changes in fatigue scores (between pre-trial scores and scores two hours after intervention) was 3.87; the score is described in detail below. The average difference in fatigue score between the vitamin C group and the placebo group was 0.85 (fatigue score) in our pilot study.
The inclusion criteria were as follows: 1) age 20 to 49 years; 2) full-time worker in the company; 3) apparently healthy; 4) no vitamin supplement intake during the two days before enrollment; and 5) voluntary participation. The exclusion criteria were as follows: 1) acute illness (such as common cold or acute gastroenteritis); 2) chronic disease (such as diabetes, hypertension, liver disease, or renal disease); 3) previous history of renal calculi or gout; 4) current pregnancy or lactation; and 5) hypersensitivity to vitamins or intravenous injection. The past medical history was investigated by research nurses and the principal investigator, a board-certified family physician, performed physical examination for the participants.
Random Assignment and Interventions
We randomly assigned participants to vitamin C and placebo groups. A computerized randomization list was generated by a statistician, sealed in an opaque envelope, and delivered to a study nurse. The study nurse attached consecutive numbers (1-150) to the normal saline bottles, and opened the envelope containing the randomization list in a closed room. She prepared solutions by mixing either vitamin C 10 g (20 ml) or normal saline 20 ml in the normal saline bottle according to the randomization list, then had no further involvement in the study. Another study nurse assigned consecutive numbers (1-150) to the participants in order of enrollment. The solution of the same number was administered to each participant by the study nurses. The participants and study nurses assessing the outcomes were blinded to the group assignment. The vitamin C group received vitamin C 10 g (20 ml of ascorbic acid 500 mg/ml, colorless transparent solution, Merit C®, Huons, Korea) in 100 ml of normal saline intravenously over 30 minutes, while the placebo group received the same amount (120 ml) of normal saline in the same manner. The intervention was performed a single time on one day.
Outcomes and Follow-up
We measured the fatigue score using a numeric rating scale (0-10), with current fatigue (described as "fatigue right now") as a primary outcome . The fatigue score was evaluated three times: before the intervention (baseline), two hours after intervention, and one day after intervention. We determined oxidative stress levels (Free Oxygen Radicals Test (FORT) by Free Oxygen Radicals Monitor Plus, Callegari, Italy) and measured plasma vitamin C concentration (by High Performance Liquid Chromatography, HPLC) at baseline and two hours after the trial. FORT was repeated one day after the trial. A UV detector (Hewlett-Packard, Germany) and a Cogent column (150mm X 4mmφ X 5um) were used for HPLC analysis with cetyltriethylammonium bromide (SIGMA, USA) and potassium dihydrogen phosphate (DUKSAN, Korea) buffers.
Assessment of Adverse Events
During intervention and at both post-intervention assessments, study nurses assessed adverse events by asking open-ended questions. Information collected for each adverse event included a description of the event, duration, intensity, required treatment, and outcome.
Analyses were performed with the "intention-to-treat" method. Predefined primary end-points were the differences in fatigue scores between two hours after intervention, and one day after intervention. The differences in fatigue scores were compared between the vitamin C group and the placebo group using analysis of covariance (ANCOVA), which included baseline fatigue score as a covariate to account for individual variations in fatigue level. As secondary end-points, oxidative stress levels were compared between the two groups using ANCOVA with similar adjustment of baseline levels. Using independent t-tests, plasma vitamin C concentrations were compared between the two groups at baseline and two hours after intervention, respectively. For subgroup analyses, subjects were categorized into two groups (higher and lower) based on the 50th percentile of the baseline vitamin C level. Change in fatigue scores between the trial and placebo group were analyzed using ANCOVA within each group.
Statistical analyses were performed using SPSS, version 16.02 (SPSS, Chicago, IL, USA). Hypothesis tests yielding p values less than 0.05 were considered significant.