1. Plasma and buffy-coat vitamin C, urinary proline, hydroxyproline, creatinine and total amino acid concentrations were measured in 23 healthy elderly subjects at intervals of 3 months.
2. There was a strong positive correlation between plasma vitamin C and buffy-coat vitamin C.
3. There were no significant correlations between plasma or buffy-coat vitamin C and total urinary hydroxyproline, whether expressed on a creatinine basis or on a total amino acid basis. Similarly, no significant correlations could be detected involving the proline/hydroxyproline ratio in urine hydrolysates.
4. There was a significant negative correlation between plasma or buffy-coat vitamin C and total urinary proline, when expressed per unit of total amino acids in the hydrolysates. This correlation was not observed with unhydrolysed urine, and it appeared to reside in the diffusible fraction, part of whose proline could be liberated by prolidase digestion. In addition, in the men, there was some evidence for a positive correlation between plasma or buffy-coat vitamin C and the ratio of total urinary amino acids to creatinine.
5. These results support the view that poor vitamin C status in elderly humans may be associated with a defect in collagen proline hydroxylation, reflected by increased excretion of proline-rich, collagen-derived peptides. If this interpretation is correct, it indicates a potential defect in connective tissue repair, and could form the basis of a functional test for subclinical vitamin C deficiency.