Free Vitamin D and Steroid Metabolism in Endocrine Disorders

NCT ID: NCT07268742

Last Updated: 2025-12-08

Basic Information

• Recruitment Status: RECRUITING
• Total Enrollment: 930 participants
• Study Classification: OBSERVATIONAL
• Study Start Date: 2024-06-01
• Study Completion Date: 2029-10-31

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

Study Design

• Observational Model Type: COHORT
• Study Time Perspective: PROSPECTIVE

Study Groups

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

Blood draw for the laboratory assessment

Intervention Type: 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

Blood draw for the laboratory assessment

Intervention Type: 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

Blood draw for the laboratory assessment

Intervention Type: 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)

Blood draw for the laboratory assessment

Intervention Type: 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

Blood draw for the laboratory assessment

Intervention Type: OTHER

Blood draw for the laboratory assessment

Healthy Controls

1. 264 individuals, consisting of;

• 132 men
• 132 women

2. Intervention - Single venous blood draw

Blood draw for the laboratory assessment

Intervention Type: OTHER

Blood draw for the laboratory assessment

Interventions

Blood draw for the laboratory assessment

Blood draw for the laboratory assessment

Intervention Type: OTHER

Eligibility Criteria

Inclusion Criteria

• 18 years or above

• 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

Exclusion Criteria

• Below 18 years of age
• Individuals incapable of providing informed consent

• 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

• Minimum Eligible Age: 18 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

KU Leuven

OTHER

Sponsor Role: collaborator

Universitaire Ziekenhuizen KU Leuven

OTHER

Sponsor Role: lead

Responsible Party

Leen Antonio

Prof. Dr.

Responsibility Role: PRINCIPAL_INVESTIGATOR

Principal Investigators

Leen Antonio, MD, PhD

Role: PRINCIPAL_INVESTIGATOR

University Hospitals Leuven, Department of Endocrinology

Locations

University Hospitals Leuven

Leuven, , Belgium

Site Status: RECRUITING

Countries

Belgium

Central Contacts

Nick Narinx, MD

Role: CONTACT

nick.narinx@uzleuven.be

+3216348516

Facility Contacts

Nick Narinx, MD

Role: primary

nick.narinx@uzleuven.be

+3216348516

Other Identifiers

S67385

Identifier Type: -

Identifier Source: org_study_id