Incremental Doses of Nitrate-Rich Beetroot Juice Do Not Modify Cognitive Function and Cerebral Blood Flow in Overweight and Obese Older Adults: A 13-Week Pilot Randomised Clinical Trial

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.

Dietary nitrate and brain health. Too much ado about nothing or a solution for dementia prevention?

“…The review also highlighted the limitations of the studies (small sample size, short duration and use of healthy populations), which could have contributed to the limited efficacy of the dietary nitrate interventions. Since the publication of the review, additional studies (50,51,52,53,54,55,56) have been published on the topic; we have summarised in Fig. 2 a selection of studies that have investigated the effects of dietary nitrate on neurocognition and CBF following supplementation for at least 1 week and conducted in subjects at greater risk of cognitive impairment.…”

“…2 a selection of studies that have investigated the effects of dietary nitrate on neurocognition and CBF following supplementation for at least 1 week and conducted in subjects at greater risk of cognitive impairment. Only two studies have concomitantly measured both neurocognition, CBF or brain metabolites (50,51) , which was measured by magnetic resonance spectroscopy (51) and near-infrared spectroscopy (50) . Five studies (50,51,53,55,56) assessed changes in cognitive function, and three (51,55,56) reported significant changes in executive function, vigilance and motor skills.…”

“…Only two studies have concomitantly measured both neurocognition, CBF or brain metabolites (50,51) , which was measured by magnetic resonance spectroscopy (51) and near-infrared spectroscopy (50) . Five studies (50,51,53,55,56) assessed changes in cognitive function, and three (51,55,56) reported significant changes in executive function, vigilance and motor skills. Four studies measured CBF or changes in brain metabolites (50,51,52,54) and the two studies reporting significant effects on CBF measured by MRI (54) and near-infrared spectroscopy (52) were conducted in participants with cardiovascular conditions suggesting greater benefits of dietary nitrate supplementation in individuals with reduced NO production.…”

“…Five studies (50,51,53,55,56) assessed changes in cognitive function, and three (51,55,56) reported significant changes in executive function, vigilance and motor skills. Four studies measured CBF or changes in brain metabolites (50,51,52,54) and the two studies reporting significant effects on CBF measured by MRI (54) and near-infrared spectroscopy (52) were conducted in participants with cardiovascular conditions suggesting greater benefits of dietary nitrate supplementation in individuals with reduced NO production. Nevertheless, while some promising results have been reported, the evidence is still contrasting.…”

“…Nevertheless, while some promising results have been reported, the evidence is still contrasting. This could be because of the short study duration (longest duration was 13 weeks (50) ), small sample size (largest sample size was sixty-two participants (50) ) and recruitment of healthy individuals with no evidence of cognitive impairment.…”