By Professor Mario Siervo, School of Population Health, Curtin University
Dietary nitrate should not be confused with organic nitrates, which are pharmacological compounds used primarily for the management of coronary heart disease.
Dietary nitrate is an essential nutrient for plant and animal physiology. In plants, dietary nitrate plays a key role in the nitrogen cycle and ensure their optimal growth.
In humans, dietary nitrate not only contributes to the regulation of nitrogen balance but also participates in several physiological functions including vascular tone regulation, immune response, and gut microbiota health.
Dietary nitrate significantly contributes to the generation of nitric oxide. NO is a soluble gas primarily produced by endothelial cells through the classical, enzymatic L-arginine-nitric oxide synthase (NOS) pathway.
However, an alternative non-enzymatic pathway called nitrate-nitrite-NO pathway also exists that converts dietary nitrate into NO through a two-step reduction process, helping maintain optimal NO production.
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When ingested, dietary nitrate is rapidly absorbed in the upper gastrointestinal tract and enters the bloodstream. While approximately 75% is excreted by the kidneys, the remaining 25% is actively concentrated in saliva by the salivary glands. The oral microbiome is crucial in this process, as bacteria on the tongue reduce salivary nitrate to nitrite.
Upon swallowing, some nitrite converts to NO in the acidic stomach environment. The remaining nitrite enters circulation, serving as a reservoir for NO generation, particularly when the oxygen-dependent NOS pathway is compromised during hypoxic or ischemic conditions.
Naturally occurring benefits
Dietary nitrate therefore represents an important alternative source of NO. Recently, it has emerged as a promising nutritional compound with significant cardiovascular benefits.
This naturally occurring molecule, abundant in green leafy and root vegetables like rocket, lettuce, spinach, beetroot and turnip, demonstrates potential for improving vascular function, reducing blood pressure, and enhancing skeletal muscle performance through its conversion to NO in the body.
The most well-documented cardiovascular effect of dietary nitrate is its ability to reduce blood pressure. Meta-analyses of randomised controlled trials have shown that dietary nitrate supplementation, typically through beetroot juice supplementation, can reduce systolic blood pressure by approximately 4 to 5 mmHg and diastolic blood pressure by 2 to 3 mmHg, with greater effects seen in individuals with elevated blood pressure.
Dietary nitrate supplementation has been linked to improved endothelial function, as measured by flow-mediated dilation (FMD), a marker of vascular health. Additional beneficial effects of dietary nitrate supplementation include a reduction of arterial stiffness, a key predictor of cardiovascular risk and inhibition of platelet aggregation.
Emerging evidence also suggests that dietary nitrate may improve cardiac efficiency by reducing oxygen consumption without compromising cardiac output, with potential benefits in patients with heart failure.
Key messages
- Dietary nitrate represents a natural and accessible approach to improve cardiovascular health.
- Promotion of the consumption of nitrate-rich foods should be considered part of comprehensive cardiovascular health management.
- As research evolves, dietary nitrate may become an important component of both primary and secondary cardiovascular disease prevention strategies.
The evidence
Several prospective cohort studies have also provided strong epidemiological evidence that higher vegetable nitrate intake is associated with reduced cardiovascular disease incidence and mortality.
These studies found that moderate vegetable nitrate consumption – approximately 60-140 mg/day – was associated with 15-27% lower risk of cardiovascular diseases, with benefits observed for ischemic heart disease, heart failure, stroke, and peripheral artery disease.
These protective effects appear to be independent of other lifestyle factors and partly mediated through blood pressure reduction, supporting the clinical findings from randomised controlled trials.
The evidence for cardiovascular benefits has increased interest in dietary nitrate supplementation as a complementary approach to cardiovascular health management.
Eating for health
Current data suggests that a daily nitrate intake of approximately 300-400 mg, equivalent to approximately 300ml of beetroot juice or about 200-300g of nitrate-rich vegetables, may be sufficient to achieve meaningful cardiovascular benefits.
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Plant-rich dietary patterns such as the Mediterranean and DASH (Dietary Approaches to Stop Hypertension) diets are widely recommended by authoritative associations and incorporated into clinical guidelines for both the prevention and management of cardiovascular diseases.
The cardiovascular benefits of these dietary patterns could be partly attributable to their high nitrate content as they can provide approximately 1000mg of nitrate, depending on vegetable choices.
Doctor’s orders
Health professionals and clinicians involved in the prevention and management of cardiovascular diseases could consider recommending increased consumption of nitrate-rich foods, particularly leafy greens like spinach, rocket, kale and lettuce, as well as beetroot as part of a heart-healthy diet.
This recommendation aligns with existing dietary guidelines that emphasise plant-based foods. For patients with established hypertension or cardiovascular disease, structured dietary approaches incorporating nitrate-rich foods may potentially serve as an adjunct to pharmacological therapy.
Author competing interests – nil
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