title: Long-term cryoconservation and stability of vitamin C in serum samples of the European prospective investigation into cancer and nutrition.
abstract: Plasma vitamin C level may be associated with risk of some chronic diseases. The rapid degradability of vitamin C in biological samples necessitates its stabilization with metaphosphoric acid or similar agents. However, in most cohort studies, prospectively collected biological samples are not treated with stabilizing agents before long-term frozen storage and it is not known whether vitamin C can be properly measured in such samples. The objective of this study was to determine the degree of vitamin C degradation in plasma samples stored without stabilization for 7 to 11 years at -196 degrees C. Spearman's correlation coefficients indicate a moderate correlation between baseline and final plasma vitamin C levels in both men (r = 0.57, P < 0.0001) and women (r = 0.52, P < 0.0001). Samples were also categorized based on low or high baseline levels of plasma vitamin C, with the latter category showing the highest rate of loss per year of frozen storage in men (1.96 micromol/L, P value for difference <0.0001; percent loss 24.6%) and women (2.35 micromol/L, P value for difference <0.0001; percent loss 24.2%), as determined by multiple regression analysis adjusted for smoking status, age, and body mass index. In men, both baseline and final plasma vitamin C values were lower in smokers than never smokers, but for both men and women the rate of vitamin C loss during storage was not significantly different between smokers and never smokers. The results of this study show that vitamin C can be measured with reasonable reliability in plasma samples frozen for long periods of time without addition of any stabilizing agents.
authors: Nutrition and Hormones Group, IARC-WHO, Lyon, France. jenab@iarc.fr
authors: Mazda
authors: M
authors: Jenab
authors: Sheila
authors: S
authors: Bingham
authors: Pietro
authors: P
authors: Ferrari
authors: Marlin D
authors: MD
authors: Friesen
authors: Wael K
authors: WK
authors: Al-Delaimy
authors: Robert
authors: R
authors: Luben
authors: Nick
authors: N
authors: Wareham
authors: Kay-Tee
authors: KT
authors: Khaw
authors: Elio
authors: E
authors: Riboli
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D001205:Ascorbic Acid / Q000097:blood*; D015925:Cryopreservation / Q000379:methods*; D004355:Drug Stability; D005060:Europe; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D012907:Smoking; D013997:Time Factors
chemical_list: D000975:Antioxidants; D001205:Ascorbic Acid