Serum ascorbic acid stability over an extended period : relevance to epidemiological studies

« Epidemiological evidence suggests that intake of vitamin C and of fruit and vegetables rich in vitamin C may reduce the risk ofcertain cancers. Most epidemiological studies have relied on estimates of vitamin C based on questionnaires because serum ascorbic acid (AA) can be very unstable. The objective of this study was to investigate the effect of extended storage at -70°C and of multiple free-thaws on AA concentration stabilized human serum from a large multi-center cervical cancer case-control study; the serum samples had been stabilized by acidification with meta-phosphoric acid and stored at -70°C. The results showed that under these conditions human serum samples are stable for periods of at least 2 years. There were indications that sample preparation in the field and freeezing and thawing the the stabilized serum samples could affect reproducibility and validity. Overall, ours results indicate that with this stabilization method, biological material collected in large-scale, multicenter studies remains usful for AA analysis for at least 2 years after collection. »