Interrelation of parathyroid hormone and vitamin D metabolites in adolescents from the UK and The Gambia

Parathyroid hormone (PTH) is used as a marker of vitamin D (VD) status. However, PTH depends on many other factors. The 24,25-dihydroxy VD (24,25VD) concentration may be a sensitive marker because its production is reduced in VD deficiency.The relationship between VD metabolites, their ratio and PTH was investigated in adolescents from the UK and The Gambia with different calcium intakes and VD status. In the UK, there was a significant positive (+ve) association between 25VD and both 1,25-dihydroxy VD (1,25VD) and 24,25VD and a negative (−ve) association with PTH. The 24,25:25VD ratio was consistent across the 25VD concentration range. There was a +ve association between PTH and 1,25:25VD, (1,25 + 24,25):25VD or 1,25:24,25VD, a −ve association with 24,25VD and none with 1,25VD or 24,25:25VD. Using LnPTH and 1,25:25VD ratio (but not 1,25VD:24,25VD or 25VD:24,25VD) increased uniformity between groups and strength of relationships compared to PTH and 1,25 or 25VD alone. In The Gambia, there was a significant −ve relationship between 25VD and PTH and none with 1,25VD. There was a +ve association between 1,25VD or 1,25:25VD and PTH.The more uniform prediction of PTH by the 1,25VD:25VD ratio may be because this better reflects the extent to which PTH-induced 1,25VD production can be met by VD supply. Further validation is needed.