Free Vitamin D and Steroid Metabolism in Endocrine Disorders

NCT07268742 | Recruiting

• 1 other identifier: S67385
• Study Type: observational
• Target: 930
• Locations: 1 country
• Sites: 1

Brief Summary

This clinical study aims to gain a better understanding of how different forms of vitamin D are processed in the body in healthy individuals, pregnant women, and patients with various hormonal (endocrine) and kidney (renal) disorders. In the long term, this study may provide new insights that could how vitamin D is tested and interpreted in these groups. Vitamin D has several important roles in the body, such as building strong bones and maintaining calcium balance in the blood. Most vitamin D in the blood circulation is attached/bound to a protein called "vitamin D binding protein" (VDBP), which makes it unavailable for the body to use. A much smaller portion circulates freely in the blood and this is called "free vitamin D". This free form can be directly used by the body. When your doctor tests your vitamin D levels, this usually refers to total vitamin D (the sum of bound and free vitamin D). However, this total value may not give an accurate indication of your actual vitamin D status, since most of it (the bound part) cannot be used by the body. The purpose of this study is to examine whether "free vitamin D" is a better marker of vitamin D status and if the amount of free vitamin D differs between healthy people, pregnant women, and people with specific endocrine or kidney disorders. Additionally, this study will look into vitamin D metabolism more detailed, and investigate what different forms of vitamin D exist, how the body processes these, and whether these forms may be related to certain endocrine or kidney conditions.

Conditions

Vitamin D; Vitamin D and Calcium Homeostasis

Keywords

Vitamin D; Free vitamin D; Free hormone hypothesis

Outcome Measures

Primary Outcomes (1)

• Direct measurement of free 25-hydroxyvitamin D3 levels

  1\) Direct measurement of free 25-hydroxyvitamin D3, reported as concentration levels per cohort; * Reported at baseline * Reported as change versus healthy control group (all cohorts vs healthy control) * Reported as change within-cohort (Pregnancy and Primary Hyperparathyroidism).

  - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

Secondary Outcomes (3)

• Calculation of free 25-hydroxyvitamin D3 levels

  - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

• Correlation of measured and calculated free 25-hydroxyvitamin D3 levels

  - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

• Laboratory assessment of vitamin D metabolite profile

  - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

Study Arms (6)

Healthy Controls

1. 264 individuals, consisting of; * 132 men * 132 women 2. Intervention - Single venous blood draw

Other: Blood draw for the laboratory assessment

Obesity

1. 132 individuals with obesity, subgrouped according to obesity class * 33 individuals with overweight, BMI 25.0-29.9 kg/m² * 33 individuals in obesity class I BMI 30.0-34.9 kg/m² * 33 individuals in obesity class II BMI 35.0-39.9 kg/m² * 33 individuals in obesity class III BMI equal to or greater than 40.0 kg/m² 2. Intervention - Single venous blood draw

Other: Blood draw for the laboratory assessment

Chronic Kidney Disease

1. 132 individuals with chronic kidney disease (CKD), subgrouped according to CKD staging; * 33 individuals in class 3a, eGFR 45 - 59 mL/min/1.73m² * 33 individuals in class 3b, eGFR 30 - 44 mL/min/1.73m² * 33 individuals in class 4, eGFR 15 - 29 mL/min/1.73m² * 33 individuals in class 5, eGFR \<15 mL/min/1.73m² 2. Intervention - Single venous blood draw

Other: Blood draw for the laboratory assessment

Pregnancy

1. 132 pregnant women; \- recruited during the first trimester of pregnancy 2. Intervention * Venous blood draw * At 4 timepoints: trimester 1 (week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery

Other: Blood draw for the laboratory assessment

Primary Hyperparathyroidism

1. 220 individuals with primary hyperparathyroidism * New diagnosis or previously untreated by surgery * With an indication for surgery (parathyroidectomy, PTX)) 2. Intervention * Venous blood draw * At 3 timepoints: at diagnosis (pre-PTX), day 1 after PTX and post-PTX (during a standard-of-care follow-up visit)

Other: Blood draw for the laboratory assessment

Complex calcium/phosphate disorders

1. Individuals with complex calcium and phosphate homeostasis disorders 2. Intervention - Single venous blood draw

Other: Blood draw for the laboratory assessment

Interventions

Blood draw for the laboratory assessment OTHER

Blood draw for the laboratory assessment

Chronic Kidney Disease; Complex calcium/phosphate disorders; Healthy Controls; Obesity; Pregnancy; Primary Hyperparathyroidism

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)
• Sampling Method: Non-Probability Sample

Study Population

* Healthy controls: community sample * Other cohorts: recruited from UZ Leuven (Academic medical center/tertiairy care center)

You may qualify if:

• \- 18 years or above

You may not qualify if:

• Below 18 years of age
• Individuals incapable of providing informed consent
• Obesity: BMI ≥ 25 kg/m2
• Chronic Kidney Disease: ≥ CKD stage 3a (eGFR \< 60 mL/min/1.73m2)
• Pregnancy: in trimester 1 of pregnancy
• Primary hyperparathyroidism: diagnosis at UZ Leuven and scheduled for parathyroidectomy at UZ Leuven
• Complex calcium and phosphate disorders: diagnosis at UZ Leuven
• Healthy controls: BMI below 18 kg/m² or above 25 kg/m², pregnancy, chronic kidney disease (independent of staging), primary hyperparathyroidism and vitamin D and/or calcium supplementation
• Obesity: chronic kidney disease (independent of staging), pregnancy, primary hyperparathyroidism
• Chronic Kidney Disease: BMI below 18 kg/m² or above 30 kg/m², pregnancy, primary hyperparathyroidism
• Pregnancy: BMI below 18 kg/m² or above 30 kg/m², chronic kidney disease (independent of staging), primary hyperparathyroidism
• Primary hyperparathyroidism: BMI below 18 kg/m² or above 30 kg/m², pregnancy, chronic kidney disease (independent of staging), secondary hyperparathyroidism

Sponsors & Collaborators

• Universitaire Ziekenhuizen KU Leuven: lead
• KU Leuven: collaborator

Study Sites (1)

University Hospitals Leuven

Leuven, 3000, Belgium

RECRUITING

Biospecimen

Retention: SAMPLES WITH DNA

Sampling by venous blood draw; * Plasma * Serum * EDTA-whole blood

MeSH Terms

Interventions

Blood Specimen Collection

Intervention Hierarchy (Ancestors)

Specimen Handling; Clinical Laboratory Techniques; Diagnostic Techniques and Procedures; Diagnosis; Punctures; Surgical Procedures, Operative; Investigative Techniques

Study Officials

• Leen Antonio, MD, PhD

  University Hospitals Leuven, Department of Endocrinology

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Nick Narinx, MD

CONTACT

+3216348516; nick.narinx@uzleuven.be

Study Design

• Study Type: observational
• Observational Model: COHORT
• Time Perspective: PROSPECTIVE
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Prof. Dr.

Study Record Dates

• First Submitted: November 21, 2025
• First Posted: December 8, 2025
• Study Start: June 1, 2024
• Primary Completion (Estimated): October 1, 2029
• Study Completion (Estimated): October 1, 2029
• Last Updated: December 8, 2025

Record last verified: 2025-12

Data Sharing

• IPD Sharing: Will not share

Locations

BE (1)