Estimation of the optimum dose of vitamin D for disease prevention in older people: Rationale, design and baseline characteristics of the BEST-D trial

Abstract

BackgroundPrevious large trials of vitamin D for prevention of fractures and other disease outcomes have reported conflicting results, possibly because the doses tested were insufficient to maintain optimum blood levels of vitamin D (25[OH]D) predicted by the observational studies. This report describes the design and baseline characteristics of the BEST-D (Biochemical Efficacy and Safety Trial of vitamin D) trial which aims to establish the best dose of vitamin D to assess in a future large outcome trial. MethodsThe BEST-D trial will compare the biochemical and other effects of daily dietary supplementation with 100μg or 50μg vitamin D3 or placebo, when administered for 12 months, in 305 ambulant community-dwelling older people living in Oxfordshire, England. The primary analyses will compare 12-month mean plasma concentrations of 25(OH)D as well as the proportion of participants with a 12-month concentration >90nmol/L between participants allocated 100μg and participants allocated 50μg daily. Secondary analyses will compare the two active doses (both separately and when combined) with placebo. Additional end-points include biochemical assessments of safety, blood pressure, arterial stiffness, falls, fractures, heel and wrist bone density, grip strength and physical performance and echocardiographic assessments of cardiac function in a random sample of participants. ResultsAbout one-third of eligible participants agreed to participate in the trial. The mean age was 72 (SD 6) years with equal numbers of men and women. About one third reported a prior history of fracture or hypertension, one-fifth reported a prior cardiovascular event, and one tenth reported diabetes or a fall in the previous 6 months. ConclusionsThe results of this trial will help determine the optimum dose of vitamin D to test in a larger trial investigating whether vitamin D supplementation can reduce the risk of fractures, cardiovascular disease or cancer.