Vitamin C concentrations in plasma as a function of intake: A meta-analysis

The purpose of this study was to estimate the intake - plasma relationship for vitamin C by means of a meta-analysis. A MEDLINE search revealed 30 publications matching our inclusion criteria. We completed the set with 5 older papers and with one monograph. The proposed statistical model corrects for inconsistencies with regard to methodological differences between the various studies. Therefore, the contribution of a particular study to the estimation is independent of the number of data points. The estimations were performed for the complete data set as well as for different subgroups: adult aged 15-65 years, elderly aged 60-96 years, non-smoker and smokers. The 50th percentile of the plasma concentration for a daily vitamin C intake of 60 mg was 42.4 mu mol/L. The corresponding values for the different subgroups were: adult 44,1 mu mol/L, elderly 31.0 mu mol/L, nonsmokers 42,4 mu mol/L, and smokers 33.6 mu mol/L. Thus, this meta-analysis confirms earlier results that the requirements of vitamin C is higher in elderly and smokers compared to adult and nonsmokers and it can be used for the estimation of the vitamin C intake in order to achieve a desired plasma level within a target population. In the general population the assumed optimal plasma concentration of 50 mu mol/L, as proposed by a consensus conference, can be achieved by the intake of 100 mg per day, which is the new recommendation of the Austrian, German, and Swiss Nutrition Societies.