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 pub lications matching our inclusion criteria. We completed the set with 5 olde r papers and with one monograph. The proposed statistical model corrects fo r inconsistencies with regard to methodological differences between the var ious studies. Therefore, the contribution of a particular study to the esti mation is independent of the number of data points. The estimations were pe rformed for the complete data set as well as for different subgroups: "adul t" 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 int ake 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, "nonsmoker s" 42,4 mu mol/L, and "smokers" 33.6 mu mol/L. Thus, this meta-analysis con firms earlier results that the requirements of vitamin C is higher in "elde rly" 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 pl asma level within a target population. In the general population the assume d optimal plasma concentration of 50 mu mol/L, as proposed by a consensus c onference, can be achieved by the intake of 100 mg per day, which is the ne w recommendation of the Austrian, German, and Swiss Nutrition Societies.