Vitamin C metabolites, independent of smoking status, significantly enhance leukocyte, but not plasma ascorbate concentrations

At 24 h, calcium ascorbate with metabolites significantly increased leukocyte vitamin C concentrations compared to ascorbic acid alone (1.3 to 1.7 times higher, p < 0.0001).

“At 24 h, calcium ascorbate with metabolites significantly increased leukocyte vitamin C concentrations compared to ascorbic acid alone (1.3 to 1.7 times higher, p < 0.0001).”

Vitamin C metabolites can enhance leukocyte vitamin C retention without altering plasma levels.

“A significant finding from these studies is that vitamin C metabolites can enhance leukocyte vitamin C retention without altering plasma levels [16,27].”

Vitamin C supplementation enhances ascorbic acid concentration in plasma and leukocytes, with a greater concentration in leukocytes when receiving vitamin C metabolites compared with ascorbic acid alone or placebo.

“Investigation of the effect of acute doses of vitamin C alone, calcium ascorbate with vitamin C metabolites, and placebo on total plasma and leukocyte vitamin C concentrations 24 h post-dosing supports the understanding that vitamin C supplementation enhances ascorbic acid concentration in plasma and leukocytes, with a greater concentration in leukocytes when receiving vitamin C metabolites comp”

Significant differences were found across preparations in leukocyte vitamin C concentrations, favoring Calcium ascorbate EC, but no differences were observed in plasma vitamin C levels.

“Significant differences were found across preparations in leukocyte vitamin C concentrations, favoring Calcium ascorbate EC, but no differences were observed in plasma vitamin C levels [16,27].”

Plasma/serum and red blood cell levels of vitamin C are tightly controlled, and vitamin C levels can differ up to 100-fold between plasma and various tissues.

“Several authors recommend using other blood and tissue markers of vitamin C to predict clinical outcomes, as plasma/serum and red blood cell levels of vitamin C are tightly controlled, and vitamin C levels can differ up to 100-fold between plasma and various tissues [16,27,42,43].”

The lower infection risk reported with Calcium ascorbate EC is consistent with reported improvements in immune cell function and in leucocyte vitamin C reported in other studies.

“The lower infection risk reported with Calcium ascorbate EC in [28] is consistent with the reported improvements in immune cell function [30] and in leucocyte vitamin C reported in other studies [16,27].”

Moyad et al. found all vitamin C interventions were significantly different from placebo for vitamin C in both plasma (p < 0.0001) and leukocytes (p < 0.0001).

“All vitamin C interventions were significantly different from placebo for vitamin C in both plasma (p < 0.0001) and leukocytes (p < 0.0001), and there were few significant differences in plasma vitamin C levels across the preparations, regardless of the post-treatment time monitoring period.”

Moyad et al. found few significant differences in plasma vitamin C levels across the preparations, regardless of the post-treatment time monitoring period.

“All vitamin C interventions were significantly different from placebo for vitamin C in both plasma (p < 0.0001) and leukocytes (p < 0.0001), and there were few significant differences in plasma vitamin C levels across the preparations, regardless of the post-treatment time monitoring period.”

Two studies assessed only males.

“Two studies assessed only males [27,31].”

Out of thirteen analyzed studies, eight (62%) did not report any adverse events for the intervention or comparators.

“Out of the thirteen analyzed studies, eight (62%) did not report any adverse events, either for the intervention or the comparators [12,27,30,31,33,35,36,37].”

From the NICE checklist quality assessment of thirteen RCTs, ten (77%) showed low risk of bias, two (15%) high risk, and one (8%) unclear risk.

“From the assessment of the methodological quality of thirteen RCTs, ten (77%) showed a low risk of bias [12,16,27,28,29,30,31,32,35,37,38], two (15%) showed a high risk of bias [33,36] and one (8%) showed an unclear risk of bias [34].”

Only four studies (31%) reported leukocyte vitamin C concentration, three (in four articles) for Calcium ascorbate EC and one for liposomal-encapsulated vitamin C.

“Only four studies (31%) reported leukocyte vitamin C concentration, three (in four articles) for Calcium ascorbate EC [16,27,30,38] and one for liposomal-encapsulated vitamin C [37].”

Calcium ascorbate EC appears to promote better vitamin C retention in leukocytes.

“Calcium ascorbate EC appears to promote better vitamin C retention in leukocytes [16,27].”

Non-linear relations were noted between changes in vitamin C concentration in plasma and leukocytes.

“Non-linear relations were noted between changes in vitamin C concentration in plasma and leukocytes [16,27].”

Studies using Calcium ascorbate EC reported favorable effects on leukocyte vitamin C concentration, showed improved immunity based on cell functions and numbers, and reported fewer colds and a shorter duration of severe cold symptoms compared to placebo.

“Studies using Calcium ascorbate EC reported favorable effects on leukocyte vitamin C concentration [16,27], showed improved immunity (based on cell functions and numbers) [30], and reported fewer colds and a shorter duration of severe cold symptoms compared to placebo [28].”

At the 1000 mg dose, the tested vitamin C interventions were significantly different from placebo regarding both plasma and leukocyte vitamin C concentrations.

“At the 1000 mg dose, the tested vitamin C interventions were significantly different from placebo regarding both plasma and leukocyte vitamin C concentrations [16,27].”

Vitamin C may enter leukocytes by first converting to dehydroascorbic acid and then back to ascorbic acid upon cell entry, which might explain enhanced absorption and bioavailability over 24 h.

“This might be due to a novel mechanism for an enhanced absorption and bioavailability of vitamin C over 24 h, whereby vitamin C enters leukocytes by first converting to dehydroascorbic acid and then back to ascorbic acid upon cell entry [27].”

Four included studies reported vitamin C concentration in both plasma and leukocytes for different formulations; two examined 1000 mg doses and two examined lower doses (250 and 500 mg).

“Four included studies reported vitamin C concentration in both plasma and leukocytes for different formulations. Two studies examined 1000 mg doses [16,27], and two examined lower doses (250 and 500 mg) [30,37].”