The VIDAL Trial recruited in 20 GP practices across England that were matched and randomised in pairs using a number of indicators.

Our primary collaborators at the Cancer Prevention Trials Unit, Queen Mary University of London created and host our unique online data capture application, the ‘VIDAL App’. The VIDAL App is an interface designed to allow users at our sites to enter all trial related data directly onto our database online via our website.

The Trial is coordinated by a small team based at the London School of Hygiene & Tropical Medicine.

Aims & Outcomes 

The primary aim of the feasibility study is to establish the procedures required to conduct the main trial. Key determinants include recruitment rate, compliance rate (proportion adhering to allocated treatment over 2 years) and contamination in both double-blind placebo control and open control practices.

Secondary objectives include providing unbiased data on the incidence of adverse events, infections, prescriptions and frequency of GP visits across both arms and estimate the bias in these measures in participants allocated to vitamin D in the open control design. We will analyse the vitamin D levels at entry and at the 2-year follow-up in relation to allocated treatments and other potential determinants of vitamin D status, particularly self-reported sun exposure.

Evaluation of the costs associated with both designs is an additional outcome to facilitate decisions regarding the design of the main trial.

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