Long-term Cryoconservation and Stability of Vitamin C in Serum Samples of the European Prospective Investigation into Cancer and Nutrition

doi:10.1158/1055-9965.EPI-05-0061

Long-term Cryoconservation and Stability of Vitamin C in Serum Samples of the European Prospective Investigation into Cancer and Nutrition

¹Nutrition and Hormones Group, IARC-WHO, Lyon, France; ²Medical Research Council Dunn Human Nutrition Unit; ³Department of Community Medicine, ⁴Institute of Public Health, and ⁵Clinical Gerontology Unit, University of Cambridge, Cambridge, United Kingdom

Requests for reprints:
Mazda Jenab, Nutrition and Hormones Group, IARC-WHO, Lyon, France. Phone: 33-4-72-738082; Fax: 11-33-4-72-738361. E-mail: jenab{at}iarc.fr

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°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 μmol/L, P value for difference <0.0001; percent loss 24.6%) and women (2.35 μmol/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.

Footnotes

Grant support: “Europe Against Cancer” Programme of the European Commission; Ligue contre le Cancer (France); Société 3M (France); Mutuelle Générale de l'Education Nationale; Institut National de la Santé et de la Recherche Médicale; German Cancer Aid; German Cancer Research Center; German Federal Ministry of Education and Research; Danish Cancer Society; Health Research Fund (FIS) of the Spanish Ministry of Health; the participating regional governments and institutions of Spain; Cancer Research UK; Medical Research Council, UK; the Stroke Association, UK; British Heart Foundation; Department of Health, UK; Food Standards Agency, UK; the Wellcome Trust, UK; Greek Ministry of Health; Greek Ministry of Education; Italian Association for Research on Cancer; Italian National Research Council; Dutch Ministry of Public Health, Welfare and Sports; Dutch Ministry of Health; Dutch Prevention Funds; LK Research Funds; Dutch Zorg Onderzoek Nederland; World Cancer Research Fund; Swedish Cancer Society; Swedish Scientific Council; Regional Government of Skane, Sweden; and Norwegian Cancer Society.
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- Accepted April 14, 2005.
- Received January 24, 2005.
- Revision received March 29, 2005.