Abstract
Nitrate-rich food increases nitric oxide (NO) production and may have beneficial effects on vascular, metabolic, and brain function. This pilot study tested the effects of prolonged consumption of a range of doses of dietary nitrate (NO3−), provided as beetroot juice, on cognitive function and cerebral blood flow (CBF) in overweight and obese older participants. The study had a 13-week single-blind, randomised, parallel design, and 62 overweight and obese older participants (aged 60 to 75 years) received the following interventions: (1) high NO3− (2 × 70 mL beetroot juice/day) (2) medium NO3− (70 mL beetroot juice/day), (3) low NO3− (70 mL beetroot juice on alternate days), or (4) placebo (70 mL of NO3−-depleted beetroot juice on alternate days). Cognitive functions were assessed using the Computerised Mental Performance Assessment System (COMPASS) assessment battery. CBF, monitored by concentration changes in oxygenated and deoxygenated haemoglobin, was assessed in the frontal cortex using near-infrared spectroscopy. The findings of this pilot study showed that cognitive function and CBF were not affected by supplementation with NO3−-rich beetroot juice for 13 weeks, irrespective of the NO3− dose administered. These findings require confirmation in larger studies using more sophisticated imaging methods (i.e., MRI) to determine whether prolonged dietary NO3− supplementation influences brain function in older overweight people.
Highlights
This paper focuses on cognitive function and cerebral blood flow (CBF)
The present study is the first to investigate the effect of 13 weeks of consumption of beetroot juice as a rich source of NO3 − on cognition and CBF in older overweight and obese individuals who are at greater risk of endothelial dysfunction and cognitive impairment
Findings from the present study provided no evidence that the 13-week ingestion of different doses of NO3 − in the form of beetroot juice had any beneficial effect on cognitive function in our participants
Summary
Ageing is associated with a progressive decline in cognitive, metabolic, and cardiovascular functions [1–3]. Vascular risk factors, including hypertension and obesity, are independently related to increased risk of cognitive decline and dementia in middle-aged and older adults [4]. 55 years or older) showed that higher baseline CBF was associated with a lower risk of cognitive decline and dementia diagnosis after a 6.5-year follow-up [10]. NO is produced via the activity of inter-connected enzymatic and non-enzymatic pathways [12] The former pathway utilises arginine as a precursor, which is converted into equimolar amounts of NO and citrulline by NO synthase, existing in three different function-specific isoforms (i.e., endothelial, inducible, and neuronal). NO is scavenged by reactive oxygen species, mainly superoxide, to form a potent oxidant called peroxynitrite [17] that reduces
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