Factors Affecting the Vitamin C Dose-Concentration Relationship: Implications for Global Vitamin C Dietary Recommendations

Abstract

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 (≤36, 37-58, ≥59 years), ethnicity (non-Hispanic white, non-Hispanic black, and total Hispanic), socioeconomic tertiles (poverty income ratios: ≤1.35, 1.36-3.0, >3.0), weight tertiles (<72, 72-91, >91 kg), BMI tertiles (<26, 26-32, >32 kg/m²) 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 ~1.2-fold higher than females to reach 'adequate' serum vitamin C concentrations of 50 µmol/L. Males had both higher body weight and a higher prevalence of smoking than females. Smokers required vitamin C intakes ~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 ~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 ~110 mg/day of vitamin C to attain adequate serum concentrations, smokers require ~165 mg/day relative to non-smokers, and heavier people (100+ kg) require ~155 mg/day to reach comparable vitamin C concentrations. These findings have important implications for global vitamin C dietary recommendations.

Keywords: NHANES; aging; ascorbic acid; body weight; obesity; smoking; socioeconomic status; vitamin C; vitamin C recommendations; vitamin C requirements.

Figure 1

Vitamin C dose-concentration relationship of the total cohort (n = 2828). Sigmoidal (four parameter logistic) curve was fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C, which is considered ‘adequate’.

Figure 2

Vitamin C dose-concentration relationship relative to gender. Female n = 1403; male n = 1425. Sigmoidal (four parameter logistic) curves were fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C, which is considered ‘adequate’.

Figure 3

Vitamin C dose-response relationship relative to smoking status. Non-smoker n = 2068; smoker n = 681. Sigmoidal (four parameter logistic) curves were fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C, which is considered ‘adequate’.

Figure 4

Vitamin C dose-response relationship relative to body weight. Lighter weight tertile 63 (57, 68) kg, n = 932; heavier weight tertile 105 (67, 118) kg, n = 930. Sigmoidal (four parameter logistic) curves were fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C, which is considered ‘adequate’.

Figure 5

Vitamin C dose-response relationship relative to age. Younger age tertile 18–36 years (n = 942) vs. older age tertile 59–80+ years (n = 944). Sigmoidal (four parameter logistic) curves were fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C, which is considered ‘adequate’. Figure reproduced from [12].

Figure 6

Vitamin C dose-response relationship relative to ethnicity. Non-Hispanic white (n = 940), and non-Hispanic black (n = 728). Sigmoidal (four parameter logistic) curves were fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C which is considered ‘adequate’.

Figure 7

Vitamin C dose-response relationship relative to socioeconomic status. Higher income to poverty ratio tertile (PIR > 3.0, n = 843), and lower income to poverty ratio tertile (PIR ≤ 1.35, n = 843). Sigmoidal (four parameter logistic) curves were fitted to the dose-concentration data with asymmetrical 95% confidence intervals indicated. Dashed line indicates 50 µmol/L serum vitamin C, which is considered ‘adequate’. PIR, poverty income ratio.