Exercise Training and Vitamin D Metabolism (Hybri-D)

The Impact of Hybrid-type High-intensity Interval Training on Vitamin D Metabolism in Adults With Overweight/Obesity

The prevalence of Vitamin D deficiency is significantly higher in adults with overweight/obesity compared to those with normal body mass index (BMI). The "entrapment" of Vitamin D in adipose tissue due to impaired lipolytic stimulation and/or adipose tissue dysfunction has been proposed as the driving mechanism. Exercise training has been proposed as a promising strategy to increase mobilization of Vitamin D from adipose tissue, given its well described role in stimulating lipolysis. Indeed, a recent study revealed that participation in moderate-intensity cardiovascular type exercise over winter can mitigate the decline in 25-hydroxyvitamin D [25(OH)D] in adults with overweight/obesity, independent of weight loss. The aim of this study is to investigate the impact of hybrid-type high-intensity interval training over winter on vitamin D metabolism, in adults with overweight/obesity.

Study Overview

• Status: Recruiting
• Conditions: Vitamin D; Obesity & Overweight
• Intervention / Treatment: Other: Exercise training; Other: Control

Detailed Description

Thirty adults with overweight/obesity (both males and females) who will meet the inclusion criteria will be randomly assigned to either an Exercise group (n=15) or a Control group (n=15). The Exercise group will participate in three hybrid-type high-intensity interval training sessions per week over a 12-week period, while receiving a balanced diet. The Control group will receive a balanced diet but will not participate in exercise training. Both groups will provide a resting blood sample and undergo assessment of their body composition (via bioelectrical impedance analysis), daily dietary intake (via dietary recalls) and physical activity level (via accelerometry) at baseline (prior to intervention), 6 weeks and 12 weeks.

• Study Type: Interventional
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Dimitrios Draganidis, PhD; Phone Number: +302431047078; Email: ddraganidis@uth.gr
• Study Contact Backup: Name: Ioannis G Fatouros, PhD; Phone Number: 2431047047; Email: ifatouros@uth.gr

Study Locations

• Greece
  • Karyes
    • Trikala, Karyes, Greece, 42100
      • Recruiting
      • Department of Physical Education and Sport Science, University of Thessaly
      • Contact: Ioannis G Fatouros, PhD; Phone Number: 2431047047; Email: ifatouros@uth.gr
      • Contact: Athanasios Z Jamurtas, PhD; Phone Number: 2431047054; Email: ajamurt@uth.gr
      • Sub-Investigator: Eytychia Giouvri, BSc

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• BMI = 25-35 kg/m2
• Absence of musculoskeletal injuries
• Absence of chronic health-related complications
• Non-smokers

Exclusion Criteria:

• Consumption of Vitamin D supplements
• Consumption of anti-inflammatory drugs, statins and/or steroids

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Exercise group; Exercise group will participate in three hybrid-type high-intensity interval training sessions per week over a 12-week period, while receiving a balanced diet	Other: Exercise training; Receive a balanced diet and participate in three hybrid-type high-intensity interval training sessions per week over a 12-week period
Active Comparator: Control group; Control group will receive a balanced diet but will not participate in exercise training	Other: Control; Receive a balanced diet but abstain from any type of exercise training

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in calcium concentration	Calcium concentration will be determined in serum	At baseline, 6 weeks and 12 weeks
Change in albumin concentration	Albumin concentration will be determined in serum	At baseline, 6 weeks and 12 weeks
Change in 25-hydroxyvitamin D concentration	25-OH-VD will be quantitatively determined in serum	At baseline, 6 weeks and 12 weeks
Change in plasma Vitamin D binding protein concentration	Vitamin D binding protein concentration will be determined in plasma	At baseline, 6 weeks and 12 weeks
Change in aspartate aminotransferase (SGOT) concentration	SGOT concentration will be determined in serum on a Clinical Chemistry analyzer	At baseline, 6 weeks and 12 weeks
Change in alanine aminotransferase (SGPT) concentration	SGPT concentration will be determined in serum on a Clinical Chemistry analyzer	At baseline, 6 weeks and 12 weeks
Change in gamma-glutamyl transferase (γ-GT) concentration	γ-GT concentration will be determined in serum on a Clinical Chemistry analyzer	At baseline, 6 weeks and 12 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in dietary intake	Dietary intake habits will be assessed through dietary recalls	At baseline, 6 weeks and 12 weeks
Change in physical activity level	Physical activity will be assessed via accelerometry	At baseline, 6 weeks and 12 weeks
Change in body composition	Body composistion will be assessed via bioelectrical impedance analysis (BIA)	At baseline, 6 weeks and 12 weeks
Change in reduced glutathione concentration	Reduced glutathione concentration will be determined in blood erythrocytes	At baseline, 6 weeks and 12 weeks
Change in oxidized glutathione concentration	Oxidized glutathione concentration will be determined in blood erythrocytes	At baseline, 6 weeks and 12 weeks

Collaborators and Investigators

• Sponsor: University of Thessaly
• Investigators: Principal Investigator: Dimitrios Draganidis, PhD, University of Thessaly

Study record dates

Study Major Dates

• Study Start (Actual): November 10, 2025
• Primary Completion (Actual): January 31, 2026
• Study Completion (Estimated): July 20, 2026

Study Registration Dates

• First Submitted: December 9, 2025
• First Submitted That Met QC Criteria: December 9, 2025
• First Posted (Actual): December 23, 2025

Study Record Updates

• Last Update Posted (Actual): May 26, 2026
• Last Update Submitted That Met QC Criteria: May 22, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: obesity; overweight; vitamin D; 25-hydroxyvitamin D; high-intensity interval training
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Overweight; Obesity; Motor Activity; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Exercise
• Other Study ID Numbers: UTH_2612_8.10.2025

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No