Effect of Vitamin D3 Supplementation on Cardiometabolic Risk Factors in a Cohort of Overweight and Obese Adults in the United Kingdom (UK)

This study is a parallel randomised, double-blind placebo - controlled trial which will be conducted at the University of Chester, Chester, United Kingdom. Ethical permission has been obtained through the University of Chester Faculty Research Ethics Committee(855/13/AT/CSN). Participants, especially students/staff will be recruited from the University of Chester by email, posters/leaflets.

Males were chosen for this study due to their higher risk of developing cardiometabolic diseases compared to premenopausal women. The participants will be randomised to receive either a vitamin D supplement (5000IU (125µg)/d) or placebo for eight weeks. A computer generated random number sequence will be used to assign participants to the intervention and placebo group. Eligibility will be based on 25(OH)D assessment made at a screening visit before the baseline visit, and participants with plasma 25(OH)D level ≤ 75nmol/l will be invited to participate in the study. To ensure compliance with the intervention, participants will be sent reminders about the intervention appointments by email or phone calls. The study will be performed according to the declaration of Helsinki. All participants will provide written consent. Study participants will be instructed to store the study supplements at room temperature. All unconsumed supplements will be returned and counted to assess compliance.

MEASUREMENTS Dietary intake will be estimated at baseline and post intervention using a three day food diary and information about health conditions, medications and health related behaviors will be assessed by a pre-screen test questionnaire, physical activity will be evaluated as the average of the metabolic equivalent of task (MET-min/week) using the International Physical Activity Questionnaire. Participants will be assessed at baseline (day 0), days 28 and 56. The plasma samples will be batch analyzed at the end of the trial.

ANTHROPOMETRIC MEASUREMENTS Height (m2) will be measured without shoes at baseline, using a stadiometer to the nearest 0.1cm precision, Body weight (kg) will be measured without shoes at baseline through post intervention using a digital scale with participants wearing light indoor clothing, BMI will be calculated as weight in kilograms divided by the square of height in meters (kg/m2), and waist circumference at the iliac crest will be measured with a tape measure with the subject standing.

PULSEWAVE VELOCITY AND BLOOD PRESSURE MEASUREMENTS Participants will be given a glass of water and allowed to rest for 5 minutes in a supine position and afterwards the pulse wave velocity meter (Arteriograph) cuff, for measuring arterial stiffness and blood pressure will be placed tightly round the dominant arm. Overall, three measurements will be performed but only the mean of two measurements will be taken.