Serum PTH is not a good marker for defining a threshold for vitamin D deficiency

• Published in: Endocrine Connections
• Main Authors: Rolf Jorde, Guri Grimnes
• Format: Article in Journal/Newspaper
• Language: English
• Published: Bioscientifica 2020
• Subjects: parathyroid hormone; thresholds; vitamin d; randomized controlled trial; Diseases of the endocrine glands. Clinical endocrinology; RC648-665; Tromsø
• Online Access: https://doi.org/10.1530/EC-20-0067; https://doaj.org/article/cc6a9851918040cc9dc9f8cccc08b986

Objective: In addition to its skeletal effects, vitamin D may also be impo rtant for health in general. It is uncertain what level of serum 25-hydroxyvitamin D (25(OH)D), marker of vitamin D status, is sufficient for these effects. With decreas ing serum 25(OH)D levels there is an increase in serum PTH. The point at which this occu rs has been considered as a threshold for vitamin D sufficiency. The thresholds found have varied widely and have mainly been based on observational studies. However, to truly e stablish a threshold for vitamin D effects, this has to be based on randomized controlled trials (RCTs). Methods: The study included 2803 subjects from a general health survey, the Tromsø study, and pooled individual person data from five vitamin D int ervention studies (n = 1544). Serum parathyroid hormone (PTH) and change in PTH after vitamin D supplementation were related to serum 25(OH)D levels in steps o f 25 nmol/L (<24, 25–49, 50–74, 75–99, and >99 nmol/L). Results: In the Tromsø study, in the females there was a gradual decrease in serum PTH with increasing serum 25(OH)D with no apparent plateau, whereas in the males the decrease in PTH in subjects with serum 25(OH)D >74 nmol/l was m arginal. In pooled RCTs, there was a significant reduction in serum PTH by vitamin D supplementation regardless of baseline serum 25(OH)D level. Conclusions: The use of the serum PTH–25(OH)D relation from observational s tudies to determine a threshold for vitamin D sufficiency is highly questio nable.