Ascorbate is an outstanding antioxidant in human blood plasma.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study using human plasma samples
PubMed 2762330 · doi:10.1073/pnas.86.16.6377
What was done
Human blood plasma was exposed in vitro to a continuous flux of aqueous peroxyl radicals to evaluate antioxidant consumption patterns (ascorbate, protein thiols, bilirubin, urate, and alpha-tocopherol) and determine the specific role of ascorbate in preventing lipid peroxidation.
What was found
The abstract reports no numerical values or effect sizes. Qualitatively, detectable lipid peroxidation occurred only after ascorbate was completely depleted. Plasma depleted of ascorbate, but containing all other endogenous antioxidants, was highly susceptible to peroxidative lipid damage. Protein thiols were oxidized rapidly upon radical exposure but functioned inefficiently as scavengers, consuming primarily through autoxidation.
Why it matters
These findings establish ascorbate as the primary physiological defense against aqueous radical-mediated lipid peroxidation in human plasma, acting before lipid-soluble or secondary antioxidants.
Limits
This was an in vitro biochemical study using an artificial free radical generator; in vivo kinetics, tissue-level oxidative stress, clinical disease endpoints, and donor sample sizes were not reported in the abstract.
Cited by
- context Entering ketosis causes a temporary spike in uric acid, which is an antioxidant with greater antioxidant capacity in human blood than vitamin C.