Evolution and the biosynthesis of ascorbic acid.
Level 5 - mechanism / opinion, no new human data
Comparative biology and evolutionary biochemistry narrative without clinical or epidemiological human data (analogous to Oxford Level 5).
PubMed 4752221 · doi:10.1126/science.182.4118.1271
What was done
The author outlined the phylogenetic distribution and tissue localization of ascorbic acid biosynthetic capability across multiple animal lineages, from invertebrates to mammals.
What was found
The abstract reports no numerical data. Qualitatively, ascorbic acid synthesis is absent in insects, invertebrates, and fishes; began in amphibian and reptile kidneys; transferred to mammalian liver; and was lost in guinea pigs, flying mammals, monkeys, and humans. A similar transition occurred across avian evolution.
Why it matters
It provides an evolutionary framework for understanding why humans and certain other animals are reliant on dietary vitamin C due to the lineage-specific loss of endogenous synthesis.
Limits
The abstract contains no quantitative metrics, sample sizes, or specific assay details. It offers a high-level qualitative overview without human clinical data.
Cited by
- supports A goat produces almost a gram of vitamin C per day endogenously in its liver.