The Effects of Vitamin D Supplementation on Aerobic Fitness in Athletes

Study Overview
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Brief Summary
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The primary aim of the study is to identify if vitamin D3 supplementation influences VO2max in athletes. Secondary aims are to determine if vitamin D3 supplementation impacts on measures of muscle function, lung function, body composition, immune function and the self-reported incidence of upper respiratory tract infection. This double-blind, randomised, placebo-controlled trial is of parallel design and will aim to recruit a total of 50 athletes randomised into either a placebo or treatment group for a 12-week intervention.

Official Title
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The Effects of Vitamin D Supplementation on VO2max in Athletes: a Randomised, Double-blind, Placebo-controlled Trial

Conditions
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Aerobic Fitness (VO2max)

Intervention / Treatment
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* Dietary Supplement: Vitamin D
* Dietary Supplement: Placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Athletes whose sport does not primarily consist of an anaerobic component Apparently healthy Over the age of 18 Exclusion Criteria: Resting arterial hypertension Individuals who are not an athlete at a University/local sports team Athletes who predominantly utilise anaerobic energy systems Athletes under the age of 18 Those that have consumed a supplement containing vitamin D (greater than 400IU/day) or iron supplements for up to 30 days prior to starting the study Those with health conditions identified by the screening questionnaire Individuals that are on prescribed medication that is known to affect vitamin D metabolism Those following a vegan diet Those with a physical disability that would prevent successful completion of the exercise test Those who have either had a sun holiday in the 4 weeks prior to starting the study Those planning a sun holiday during the intervention period

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Vitamin D3 3000IU (75μg)<br>Treatment solution delivered via oral spray once daily for 12-weeks | Dietary Supplement: Vitamin D<br>* 3000IU (75 μg) vitamin D in a commercially available oral spray solution<br>* Other names: vitamin D3;|
| Placebo Comparator: Placebo<br>Placebo solution delivered via oral spray once daily for 12-weeks | Dietary Supplement: Placebo<br>* Placebo oral spray solution manufactured to mimic the vitamin D oral spray<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Aerobic fitness (VO2max) | A medical screening questionnaire will be completed prior to the test. Athletes resting blood pressure will be measured twice to rule out resting hypertension. After a standardised warm-up, starting speed will be 8/km/hr at 1% incline, until 17/km/hr, after which incline will increase by 1% every minute until VO2max is met. A metabolic cart (Metalyzer 3B) will measure the athlete's ventilation (oxygen uptake and carbon dioxide output) throughout the test. The test will be terminated when two of the following criterion are met*: Respiratory exchange ratio reaches/exceeds 1.15 AND VO2 plateau observed OR Heart rate within 10bpm of age-predicted maximum * Except when volitional exhaustion occurs Athletes will be asked to refrain from strenuous activity for 24 hours prior to VO2max testing in order to control for last bout effects. Post-exercise lactate concentration (age and gender adjusted) will further-verify that VO2max was attained using a Lactate Pro device. | At baseline and at 12-weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Hand grip strength | Hand grip dynamometry will be used to assess athletes grip strength. This will be measured on both dominant and non-dominant hands three times. The athlete will be asked to hold the device and grip as tightly as possible whilst holding the device alongside their body. There will be a 10 second rest period between measurements. | At baseline and at 12-weeks | 
| Vertical jump height | Athletes will be asked to reach upwards as far as possible, from a standing position and mark this point on a wall. After this they will be asked to perform a counter-movement jump a total of 3 times with a 10 second rest-period between jumps, reaching as high as possible and making a mark each time. Vertical jump height is calculated from the difference between standing reach height and the best height reached when performing a counter-movement jump. | At baseline and at 12-weeks | 
| Lung function | Forced expiratory volume at 1 second (FEV1) and forced vital capacity (FVC) will be measured. A calibrated Carefusion® MicroLab portable spirometer will be used to measure these variables.The athletes will need to take a maximal inhalation and then perform a full exhalation as fast as possible into a disposable mouthpiece. This procedure will be repeated three times and an average taken at each time-point. The timing of repeats will be at the athletes discretion. | At baseline and at 12-weeks | 
| Nutrient intake | Dietary vitamin D and calcium intake will be estimated using a validated food frequency questionnaire at one time point (baseline only). This is due to studies highlighting equivocal variation in dietary vitamin D intake throughout the year. 24hr recalls will be completed at baseline and at 12-weeks in order to derive mean nutrient intakes for the vitamin D and placebo treatment groups respectively. | At baseline only/ at baseline and at 12-weeks | 
| Self-reported upper respiratory illness | An online questionnaire will allow athletes to record if they have any symptoms that are associated with upper respiratory infections. The athlete will be asked to mark a series of boxes to indicate how many symptom(s) if any that they have had each week. | Once per week up to week 12 | 
| Physical activity levels | The 'Modified Recent Physical Activity Questionnaire' produced by the Medical Research Council (a validated physical activity questionnaire) will be completed on two occasions to estimate physical activity levels. | At baseline and at 12-weeks | 
| Body composition | Body composition will be measured using the BodPod, employing air plethysmography (displacement of air) to accurately measure percentage fat mass and percentage fat-free mass. | At baseline and at 12-weeks | 
| Vitamin D status | 25-hydroxyvitamin D (25(OH)D) will be quantified, in serum, using liquid chromatography-tandem mass spectrometry (LCMS/MS). Other biomarkers of vitamin D metabolism (adjusted calcium and parathyroid hormone) will be quantified using a clinical chemistry analyser and commercially available enzyme-linked immunosorbent assay. | At baseline and at 12-weeks | 
| Immune function | A range of immune markers such as interleukin-6, cathelicidin (LL-37) and C-reactive protein will be measured using a commercially available multiplex immunoassay. | At baseline and at 12-weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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fitness, vitamin D, athletes