Inverse Relationship Between 25 Hydroxy Vitamin D and Parathormone: Are there Two Inflection Points?

Area of Science:

• Endocrinology
• Nutritional Science
• Public Health

Background:

• Consensus is lacking regarding the specific 25 hydroxy vitamin D (25(OH)D) threshold below which intact parathyroid hormone (PTH) levels begin to rise.
• Understanding this relationship is crucial for defining vitamin D deficiency and sufficiency accurately.

Purpose of the Study:

• To determine the precise relationship and identify inflection points between 25(OH)D and intact PTH levels.
• To evaluate existing cut-offs for vitamin D status in relation to PTH response.

Main Methods:

• Population-based analysis conducted on a nonobese cohort (n = 405).
• Statistical analysis, including LOWESS method, to identify inflection points in the 25(OH)D-PTH relationship.

Main Results:

• Prevalence of vitamin D deficiency (58.76%) and insufficiency (34.56%) was high in the cohort.
• A weak inverse relationship (r = -0.16, P = 0.018) was observed between 25(OH)D and intact PTH.
• Two significant inflection points were identified: one at 32 ng/mL (corroborating sufficiency definitions) and a steeper one at 16.5 ng/mL (aligning with deficiency definitions).

Conclusions:

• The study suggests two critical inflection points in the 25(OH)D-PTH relationship.
• These findings support the existence of distinct thresholds for vitamin D deficiency and sufficiency, with implications for clinical practice and public health guidelines.