Vitamin C - a scoping review for Nordic Nutrition Recommendations 2023

Abstract

Vitamin C has multiple metabolic functions in the body, but the available information on the exact relationship between these functions and the intake necessary to maintain them is very limited. However, most attempts to objectively measure adequacy of vitamin C status, including, for example, replacement of metabolic turnover, chronic disease prevention, urinary excretion, and saturation of immune cells and body compartment, currently point toward 50 µmol/L as a reasonable target plasma concentration. As a strong correlation between body weight and vitamin C status exists, recommended intakes (RIs) for other age groups may be extrapolated from the adult RI based on weight. However, as body weights above 70 kg are becoming increasingly common - also in the Nordic region - an RI of 140 mg/day for individuals weighing 100 kg or more should be considered to compensate for the larger volume of distribution. Finally, smoking continues to be a common contributor to poor vitamin C status; therefore, it is proposed that people who smoke increase their daily vitamin C intake by 40 mg/day to compensate for the increased metabolic turnover induced by smoking.

Keywords: antioxidants; ascorbic acid; nutrition recommendations; vitamin C.

Fig. 1

Search strategy to identify relevant meta-analyses for inclusion.

Fig. 2

Chemical structures of ascorbic acid, ascorbyl free radical, and dehydroascorbic acid.

Fig. 3

Plasma ascorbate concentrations in healthy volunteers as a function of daily dose. Figure from (65); Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 4

Decreasing plasma ascorbate concentrations with increasing body weight (A) and increasing vitamin C requirements with increasing body weight (B). The dashed line represents extrapolation of the weight data points. Figure from (65); Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 5

Analysis of NHANES 2017/2018 data indicated a twofold higher requirement for vitamin C for the heavier tertile (n = 930) relative to the lighter tertile (n = 932). Sigmoidal (four-parameter logistic) curves with asymmetrical 95% confidence intervals were fitted to dose-concentration data to estimate the vitamin C intakes required to reach ‘adequate’ serum vitamin C concentrations of 50 µmol/L (dashed line). Figure from (74); Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 6

Analysis of NHANES 2017/2018 data indicated a twofold higher requirement for vitamin C for smokers (n = 681) relative to non-smokers (n = 2,068). Sigmoidal (four-parameter logistic) curves with asymmetrical 95% confidence intervals were fitted to dose-concentration data to estimate the vitamin C intakes required to reach ‘adequate’ serum vitamin C concentrations of 50 µmol/L (dashed line). Figure from (74); Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 7

Coronary heart disease risk relative to vitamin C dietary intake (A) and blood concentrations (B): dose-response analyses. Similar trends were observed for stroke and cardiovascular disease. Solid lines represent best-fitting cubic spline and dashed lines 95% CI. Reproduced from (22); Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/).