Vitamin C status is known to be associated with several demographic and lifestyle factors. These include gender, age, ethnicity, pregnancy/lactation, body weight, smoking status and dietary habits. In the present study, our aim was to investigate the National Health and Nutrition Examination Survey (NHANES) 2017-2018 datasets to assess the impact of these factors on vitamin C dose-concentration relationships to establish if there are higher requirements for vitamin C in certain subpopulations, and the possible extent of these additional requirements. The final cohort comprised 2828 non-supplementing adult males and females (aged 18-80+ years) with both vitamin C serum concentrations and dietary intake data available. The data were subsequently stratified by gender, age tertiles (= 59 years), ethnicity (non-Hispanic white, non-Hispanic black, and total Hispanic), socioeconomic tertiles (poverty income ratios: 3.0), weight tertiles (91 kg), BMI tertiles (32 kg/m(2)) and smoking status. Sigmoidal (four parameter logistic) curves with asymmetrical 95% confidence intervals were fitted to the dose concentration data. We found that males required vitamin C intakes similar to 1.2-fold higher than females to reach adequate' serum vitamin C concentrations of 50 mu mol/L. Males had both higher body weight and a higher prevalence of smoking than females. Smokers required vitamin C intakes similar to 2.0-fold higher than non-smokers to reach adequate vitamin C concentrations. Relative to adults in the lighter weight tertile, adults in the heavier weight tertile required similar to 2.0-fold higher dietary intakes of vitamin C to reach adequate serum concentrations. We did not observe any impact of ethnicity or socioeconomic status on the vitamin C dose-concentration relationship, and although no significant difference between younger and older adults was observed at vitamin C intakes > 75 mg/day, at intakes < 75 mg/day, older adults had an attenuated serum response to vitamin C intake. In conclusion, certain demographic and lifestyle factors, specifically gender, smoking and body weight, have a significant impact on vitamin C requirements. Overall, the data indicate that the general population should consume similar to 110 mg/day of vitamin C to attain adequate serum concentrations, smokers require similar to 165 mg/day relative to non-smokers, and heavier people (100+ kg) require similar to 155 mg/day to reach comparable vitamin C concentrations. These findings have important implications for global vitamin C dietary recommendations.