Vitamin D deficiency is considered a public health priority in the UK, with approximately 30-40% of the UK population being deemed vitamin D deficient during winter months. Current government strategies to improve vitamin D status amongst the UK population involve dietary supplementation, however, it has been shown that excess adiposity reduces the impact of dietary supplementation with vitamin D. One potential explanation for this observation is that vitamin D becomes sequestered in adipose tissue. We hypothesise that exercise may facilitate the mobilisation of vitamin D from adipose tissue and thus increase circulating vitamin D (25OHD) concentrations. Little is currently known as to whether a single bout of exercise affects vitamin D status, with a handful of studies demonstrating contradictory findings. This research will examine the effect of an acute bout of exercise (treadmill-based at 60% VO2 Max for 60 minutes) on vitamin D status (serum 25(OH)D) in healthy community-dwelling adults.

This study is a random crossover design and will require 34 participants to visit the University of Bath on 6 separate occasions in total.

Individuals who express an interest in taking part will be invited to attend an initial screening meeting at the University so that the eligibility can be assessed for the study, and the all procedures explained verbally. If the participant is eligible and is happy to participate in the study, they will attend a second visit prior to two trials to undertake a treadmill-based maximal exercise test (VO2 Max), resting metabolic rate measure and several measures will be taken to assess body composition. Trials will involve a 60-minute exercise bout at 60% of the participant's maximum oxygen uptake or a 60-minute resting period (both followed by a further hour of rest). The order in which these trials occur will be randomised for each participant and the participant will not be told of this order prior to the trials.

During both trials, a cannula will be inserted into a vein in the arm prior to exercise and 10ml blood samples will be drawn at baseline (pre-exercise) and immediately after the exercise session and 1 hour post exercise from the antecubital vein. The participant will return to the university the day after each trial for a 10ml venous blood sample (24hr post-exercise) which will be taken via venepuncture. In the 24 hours following a trial, participants will be provided with standardised meals in order to ensure energy balance. Other controls which will be applied during the study period will include the provision of factor 50 sunscreen (if the participant is undertaking trials between March and October) to aid in mitigating against the cutaneous synthesis of vitamin D, and guidance on avoiding any strenuous activity 24 hours prior to trial days. Participants will also be provided with a physical activity monitor (MotionWatch8, CamNTech) to wear during trial days after leaving the lab.

Inclusion Criteria:

• Healthy (see exclusion criteria)
• 25-65 years old
• Ability to travel to and from University of Bath campus

Exclusion Criteria:

• Current or recent use (within the last three months) of weight loss drugs, medication that would interfere with study outcomes, sunbeds, or dietary vitamin D supplementation
• Change in weight of more than 5% in the last six months, or a significant change in lifestyle in the last two months
• Positive responses to the Physical Activity Readiness Questionnaire (PAR-Q)
• Presence of coronary heart disease, chronic kidney disease, type 2 diabetes, stroke, heart failure, peripheral arterial disease, severe hypertension (blood pressure >180/110 mmHg)
• BMI <18kg/m2 or BMI >40kg/m2

Healthy, community-dwelling adults (aged 25-65 years old)