Re: "Vitamin C deficiency in a population of young Canadian adults".

In their report that nearly 50% of healthy young Canadian adults have subnormal serum vitamin C concentrations, Cahill et al. (1) cite our observation that 60% of the acute-care patients in a tertiary care Montreal hospital had subnormal plasma vitamin C concentrations (2). More pertinently, we also observed that only 13% of people concurrently attending the hospital’s outpatient test center had a subnormal plasma vitamin C concentration (2). The method used by Cahill et al. (1) for handling, storing, and analyzing serum vitamin C is questionable. To prevent vitamin C degradation, whole blood samples must be kept cold at all times, and as soon as the plasma is obtained it must immediately be stabilized by ice-cold deproteinization or flash frozen with ethanol-dry ice with prompt storage at 70 C to 80 C (3, 4). If not stored at 70 C to 80 C, vitamin C will disappear even from deproteinized plasma samples. The serum samples in the reported study were neither deproteinized nor flash frozen prior to storage, and they were stored at only 20 C. The high performance liquid chromatography detection method is not identified or described, precluding an assessment of its reliability.