Protocol and recruitment results from a 13-week randomized controlled trial comparing the effects of different doses of nitrate-rich beetroot juice on cognition, cerebral blood flow and peripheral vascular function in overweight and obese older people.

Nitrate-rich food can increase NO production and may induce positive effects on brain function. This study examined the feasibility of a randomized clinical trial (RCT) testing the effects of prolonged consumption of incremental doses of dietary nitrate (NO₃^-) in overweight and obese older participants. Secondary aims tested dose-dependent changes in cognitive, vascular and pulmonary functions and cerebral blood flow (CBF).

This was a single blind, four-arm parallel RCT conducted in 60 overweight and obese older participants. Eligible participants were randomized to:1) high NO₃^- (140 ml of beetroot juice (BJ) per day, ~800 mg of NO₃^-/day), 2) moderate NO₃^- (70 ml of BJ per day, ~400 mg of NO₃^-/day), 3) low NO₃^- (70 ml on alternate days, ~400 mg of NO₃^-) or 4) NO₃^- depleted (70 ml on alternate days, ~0.001 mg of NO₃). Measurements of cognitive, vascular and pulmonary functions and CBF were conducted at baseline and 13-weeks NO₃^- intake was assessed by six 24-h recalls, and by measuring NO₃^- intake biomarkers. Feasibility was assessed by obtaining qualitative feedback and evaluating trial recruitment, retention, compliance with study visits and measurement protocols.

Participant recruitment started in July 2018 and ended in April 2019. Of all the recruitment strategies that were used, advertisement of the study via Facebook generated the highest response rate. Sixty-two participants consented and were enrolled. Overall, characteristics of included participants matched our recruitment criteria.The findings from this study provide evidence of the acceptability and feasibility of an intervention investigating the effects of incremental doses of high-nitrate BJ over a prolonged period.The intervention study was registered with clinical trial ISRCTN registry (ISRCTN14746723) on 27 December 2018.