Vitamin C – or ascorbic acid – exists in the circulation bound to albumin. It acts as cofactor for several hydroxylation reactions eg. in collagen and carnitine synthesis, and as cofactor in metabolism of several drugs and nutrients. It is also a powerful antioxidant and is involved in optimal leukocyte function.
Vitamin C deficiency is rare in developed countries since it is preventable by the intake of as little as 10mg daily (recommended intake is 90mg/day for men and 75mg/day for women). However, in some situations of abnormal diet, it may occur in the very young and very old. Early symptoms are of fatigue followed by easy bruising, bleeding, hair loss, joint pain and swelling.
There is evidence that a healthy intake of fruit and vegetables provides enough vitamin C to protects against stroke, cardiovascular disease, and most forms of cancer.
The nutritional status of vitamin C can be assessed by HPLC measurement of plasma levels. It is important to note that concentrations are influenced by recent dietary intake and particularly by the acute phase response which lowers levels substantially.
Vitamin C is essentially non-toxic with the possible exception of very high dietary intake.
Sample Requirements and Reference Ranges for Vitamin C
| Sample Type | Plasma or serum |
|---|---|
| Container | Lithium heparin, EDTA, or plain. SST unsuitable. |
| Precautions | Vitamin C is very unstable and so samples require to be treated within 4 hours of collection. Mix 1:1 ratio of plasma with 6% metaphosphoric acid** (Sigma, catalogue no. M-5043 or BDH catalogue no. 291904A) for 30s. Deliver to Glasgow within 24h or, if delivery is outwith 24 hours, freeze treated plasma until sending and then send on ice, or preferably dry ice. |
| Minimum volume* | 650 µL of stabilised plasma |
| Reference range | 15 to 90 µmol/L < 10 µmol/L (risk of developing symptoms of deficiency) |
| Turnaround time | 1 week |
| Method | HPLC with electrochemical detection |
* This is the absolute minimum volume; these volumes are insufficient to carry out a repeat analysis in the event of an analytical problem.
** 6% metaphosphoric acid is stable for 3 weeks.