Vitamin DFREEDOMNCT07268742
Free Vitamin D and Steroid Metabolism in Endocrine Disorders
An observational study of Vitamin D and Vitamin D and Calcium Homeostasis, run by Universitaire Ziekenhuizen KU Leuven at 1 site in Belgium.
Trial 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. Read more about this study
- Who is it for?
- Ages 18 years and olderHealthy volunteers can take part
- Conditions the study is for
- Vitamin D, Vitamin D and Calcium Homeostasis
- What is being tested?
- Blood draw for the laboratory assessment
- How many people
- 930 participants
- Where
- 1 siteBelgium
- Study dates
- 1 Jun 2024to Oct 2029
- Phase
- Observational
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Study population: * Healthy controls: community sample * Other cohorts: recruited from UZ Leuven (Academic medical center/tertiairy care center)
- General inclusion Criteria:
- 18 years or above
- General exclusion Criteria:
- Below 18 years of age
- Individuals incapable of providing informed consent
- Cohort inclusion criteria
- 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
- Cohort exclusion criteria
- 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
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Belgium1 site, 1 recruiting
- Recruiting
University Hospitals Leuven
Leuven, 3000
Nick Narinx, MD, +3216348516, nick.narinx@uzleuven.be
About this study
Official title: Free Fraction Vitamin D Measurements to Improve Understanding of Steroid Metabolism in Endocrine Disorders
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.
Read more
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
- Being tested
- Blood draw for the laboratory assessment
- Keywords
- Vitamin D, Free vitamin D, Free hormone hypothesis
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Blood draw for the laboratory assessmentOther
Blood draw for the laboratory assessment
| Study group | Role | What they receive |
|---|---|---|
| Healthy Controls | 1. 264 individuals, consisting of;
* 132 men
* 132 women
2. Intervention - Single venous blood draw Receives: 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 Receives: 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 Receives: 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 Receives: 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) Receives: 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 Receives: Other: Blood draw for the laboratory assessment |
What is being measured
The primary outcome is the main question the study is designed to answer.
Direct measurement of free 25-hydroxyvitamin D3 levels
- 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).
Measured: - 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
- Calculation 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).
Measured: - 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
Assessment of correlation between measured (Primary Outcome) and calculated (Secondary Outcome 1) free 25-hydroxyvitamin D3 levels
Measured: - 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
Laboratory assessment of different vitamin D metabolites;
- 25-hydroxyvitamin D3
- 3-epi-hydroxyvitamin D3
- 1(alpha).25-dihydroxyvitamin D3
- 1(beta).25-dihydroxyvitamin D3
- 3-epi-1.25-dihydroxyvitamin D3
- 24.25-dihydroxyvitamin D3
- 25-hydroxyvitamin D2
- 1.25-dihydroxyvitamin D2
Measured: - 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)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted8 Dec 2025
- Study start1 Jun 2024
- Primary completionOct 2029 (estimated)
- Study completionOct 2029 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Vitamin DStudies of the same condition, open and under way.
- More trials run by Universitaire Ziekenhuizen KU LeuvenThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Cohort
- Time perspective
- Prospective
- Enrolment
- 930 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Universitaire Ziekenhuizen KU Leuven
- Sponsor type
- University, hospital or other
- Collaborators
- KU Leuven
- Responsible party
- Principal investigator, Leen Antonio, Universitaire Ziekenhuizen KU Leuven
- Investigators
- Leen Antonio, MD, PhD, Principal investigator, University Hospitals Leuven, Department of Endocrinology
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07268742
- Sponsor's protocol ID
- S67385
- Acronym
- FREEDOM
- Status last verified
- Dec 2025
- First submitted
- 21 Nov 2025
- Last updated
- 8 Dec 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 8 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Free Fraction Vitamin D Measurements to Improve Understanding of Steroid Metabolism in Endocrine Disorders
- ClinicalTrials.gov ID
- NCT07268742
- Acronym / sponsor ID
- FREEDOM / S67385
- Conditions
- Vitamin D, Vitamin D and Calcium Homeostasis
- Keywords
- Vitamin D, Free vitamin D, Free hormone hypothesis
- Study type
- Observational
- Recruitment status
- Recruiting
- Enrolment
- 930 participants (estimated)
- Lead sponsor
- Universitaire Ziekenhuizen KU LeuvenUniversity, hospital or other
- Collaborators
- KU Leuven
- Study start
- 1 Jun 2024 (actual)
- Primary completion
- Oct 2029 (estimated)
- Study completion
- Oct 2029 (estimated)
- First posted
- 8 Dec 2025 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Study design
- Observational model
- Cohort
- Time perspective
- Prospective
- Number of arms
- 6
| Arm | Type | Receives |
|---|---|---|
| Healthy Controls | – | Other: Blood draw for the laboratory assessment1. 264 individuals, consisting of; * 132 men * 132 women 2. Intervention - Single venous blood draw |
| Obesity | – | Other: Blood draw for the laboratory assessment1. 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 |
| Chronic Kidney Disease | – | Other: Blood draw for the laboratory assessment1. 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 |
| Pregnancy | – | Other: Blood draw for the laboratory assessment1. 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 |
| Primary Hyperparathyroidism | – | Other: Blood draw for the laboratory assessment1. 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) |
| Complex calcium/phosphate disorders | – | Other: Blood draw for the laboratory assessment1. Individuals with complex calcium and phosphate homeostasis disorders 2. Intervention - Single venous blood draw |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
- Study population
- * Healthy controls: community sample * Other cohorts: recruited from UZ Leuven (Academic medical center/tertiairy care center)
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Blood draw for the laboratory assessmentBlood draw for the laboratory assessment | Other | Chronic Kidney Disease, Complex calcium/phosphate disorders, Healthy Controls, Obesity, Pregnancy, Primary Hyperparathyroidism |
Primary outcome
Direct measurement of free 25-hydroxyvitamin D3 levels
Time frame: - 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)
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).
3 secondary outcomes
Calculation of free 25-hydroxyvitamin D3 levels
Time frame: - 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
Time frame: - 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
Time frame: - 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)
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 8 Dec 2025.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Leen Antonio, MD, PhD principal investigator
University Hospitals Leuven, Department of Endocrinology
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
An observational study of Vitamin D and Vitamin D and Calcium Homeostasis, run by Universitaire Ziekenhuizen KU Leuven at 1 site in Belgium.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 8 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Belgium. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Nick Narinx, MD (+3216348516, nick.narinx@uzleuven.be), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Direct measurement of free 25-hydroxyvitamin D3 levels (time frame: - 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)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 8 Dec 2025.