In Sub-Saharan Africa, current strategies are struggling to control the burgeoning hypertension epidemic but dietary interventions such as inorganic nitrate or folic acid supplementation could represent promising strategies for reducing blood pressure (BP).
Dietary inorganic nitrate, found in large quantities in green leafy vegetables and beetroot, serves as a substrate for the pleiotropic gasotransmitter nitric oxide (NO) and has attracted considerable interest in the past decade as a nutritional antihypertensive agent.
Given that dietary nitrate and folic acid operate, at least in part, through separate mechanisms, it is possible that they may elicit additive or synergistic effects on BP. However, prior to this study, there was no data on the combined effects of consuming both.
A team of researchers from Newscastle University, in the UK, and Kilimanjaro Christian Medical University College, in Tanzania, carried out a double-blind randomised controlled feasibility trial to discover the effects of each of the supplements, alone or in combination, on BP in Tanzanian adults with high BP.
Using a sample of nearly 50 adults, they found a significant decrease in BP in those given high-nitrate beetroot juice group, whereas changes were not significant in the those given the combined supplements.
Their report, published in 'The Journal of Nutrition', concludes: "Dietary inorganic nitrate represents a potential nutritional strategy to lessen the hypertension epidemic in Sub-Saharan Africa. These findings support the rationale for future long-term investigations exploring the efficacy of dietary nitrate for lowering BP and attenuating cardiovascular disease risk in this setting."
The study
Forty-seven middle-aged and older participants (age: 50–70 y, BMI: 26.3–29.1 kg/m2) were randomly assigned to three conditions for a period of 60 days.
The three groups were supplemented with: High-nitrate beetroot juice (∼400 mg nitrate) and folic acid (5 mg) (N + F), high-nitrate beetroot juice and placebo (N + P), or nitrate-depleted beetroot juice and placebo (P + P).
Clinic and 24-hour ambulatory BP and measurements of compliance in plasma (nitrate and folate concentrations) and saliva (nitrate and nitrite) were obtained at baseline, then after 30 days, and 60 days.
Results
Baseline resting systolic and diastolic BP (mean ± SD) was 151.0 ± 19.4 mm Hg and 91.8 ± 11.7 mm Hg, respectively. Compliance to the interventions was high (>90%) in all groups which was confirmed by the significant increase in nitrate and folic acid concentrations in plasma and saliva samples in the treatment arms.
After 60 days, 24-h systolic BP dropped by −10.8 ± 9.8 mm Hg (P < 0.001), −6.1 ± 13.2 mm Hg (P = 0.03), and −0.3 ± 9.7 mm Hg (P = 0.83) in the N + P, N + F, and P + P groups, respectively.
There was a significant decrease in 24-h diastolic BP in the N + P group (−5.4 ± 5.0 mm Hg, P = 0.004), whereas changes were not significant in the N + F (−1.8 ± 8.1 mm Hg, P = 0.32) and P + P (1.6 ± 8.3 mm Hg, P = 0.43) groups.
Prior research
In their seminal study, Larsen et al. reported a 3.7 mm Hg decrease in diastolic BP after 3 d supplementation with sodium nitrate. Subsequently, Webb et al. reported a ∼10.4 mm Hg and ∼8.0 mm Hg reduction in systolic and diastolic BP, respectively, 2.5–3 h after acute ingestion of nitrate-rich beetroot juice. Similar benefits have also been reported in a group of African-American women.
A recent meta-analysis reported overall reductions in systolic and diastolic BP of 4.8 mm Hg and 1.7 mm Hg, respectively, after dietary nitrate supplementation. Folic acid has also attracted attention as a potential BP-reducing nutritional compound.
It has been demonstrated to improve endothelial function and reduce BP: effects which may be underpinned by improved NO synthase coupling, scavenging of superoxide, and a reduction in homocysteine.
Source: The Journal of Nutrition
Siervo. M., et al
"Nitrate-Rich Beetroot Juice Reduces Blood Pressure in Tanzanian Adults with Elevated Blood Pressure: A Double-Blind Randomized Controlled Feasibility Trial"