The importance of vitamin C for hydroxylation of vitamin D3 to 1,25(OH)2D3 in man.
The effects of vitamin C on 1,25(OH)2D3 synthesis in humans were evaluated; the study included 20 females. They were divided into 2 groups. The first of the 10 subjects (age range 55-71) received ascorbic acid at a dose of 150 mg/die i.v. for 10 days; the second 10 subjects (age range 55-69) received a placebo i.v. for 10 days. In a later study (after a 30-day washout) the same two groups were tested for the second time with ascorbic acid at a dose of 1,000 mg/die i.v. for 10 days and placebo i.v. for 10 days. Serum calcium and phosphorus, serum Ca++, serum proteins, blood and urinary pH, serum 25(OH)D3 and 1,25(OH)2D3, serum PTH, urinary hydroxyprolin were tested before and after the treatments. In the first study a significant increase in serum 1,25(OH)2D3 was observed after ascorbic acid while no significant variation was observed for the other parameters. In the second study, a significant increase in serum Ca++ and a significant decrease in serum 1,25(OH)2D3 were observed after ascorbic acid while no significant variation was observed for the other parameters. The authors conclude that ascorbic acid promotes 1,25(OH)2D3 synthesis at a paraphysiologic dose (150 mg/die) in humans but this synthesis is inhibited at higher doses (1,000 mg/die). The latter effect by Ca++ or by an effect of ascorbate on 1 alpha-hydroxylase enzyme could be mediated.
Cantatore
F P
FP
Department of Rheumatology, University of Bari, Italy.
Loperfido
M C
MC
Magli
D M
DM
Mancini
L
L
Carrozzo
M
M
D000328:Adult; D000368:Aged; D001205:Ascorbic Acid / Q000494:pharmacology*; D002117:Calcitriol / Q000096:biosynthesis*; D002118:Calcium / Q000097:blood; D002762:Cholecalciferol / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006900:Hydroxylation; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood
D010281:Parathyroid Hormone; D002762:Cholecalciferol; D010758:Phosphorus; D002117:Calcitriol; D001205:Ascorbic Acid; D002118:Calcium