Nitric oxide levels fall with age — and this decline is linked to an array of age-related problems in areas like heart, brain, reproductive, and muscle health [1][2]. Nitric oxide acts as a critical signalling molecule in blood vessels: it prompts smooth muscle cells to relax, widening the vessel and improving blood flow throughout the body. As this capacity diminishes with age, blood pressure tends to rise and exercise capacity can decline [1].
Predatory supplement brands are quick to capitalise on this, spinning a story that their pill will reverse the decline. The clinical evidence tells a more nuanced — and ultimately more useful — story.
There is a cheap and remarkably effective whole-food approach to supporting nitric oxide — one that outperforms most supplements on the market and costs next to nothing per serving.
Table of Contents
- Why You Can't Just Swallow Nitric Oxide
- The Supplement Approach: L-Arginine and L-Citrulline
- The Nitrate Pathway: Beetroot Juice
- Tadalafil: A Different Kind of NO Booster
- Arugula: The Evidence-Based Whole-Food Alternative
- References
Why You Can't Just Swallow Nitric Oxide
Nitric oxide itself is an incredibly unstable gas — it cannot simply be swallowed. Raising nitric oxide levels in blood vessels requires indirect strategies. The intravascular half-life of nitric oxide is approximately 2 milliseconds [3] — it disappears almost as soon as it is made.
Pharmaceutical manufacturers addressed this problem decades ago. Prescription medications like GTN (glyceryl trinitrate) sprays and isosorbide mononitrate (ISMN) result in nitric oxide production where it is needed in the body. These are effective for acute management of conditions like angina. However, these are prescription medications, not suitable for general use, and come with important limitations.
There is an Achilles' heel with medications like ISMN: the body rapidly builds tolerance, and they lose much of their effectiveness over time [4]. That is because of the way these drugs work — they do not support the body's own nitric oxide system, they bypass it. They act more like short-acting jolts that force blood vessels to relax. Over time, the body adapts and stops responding as strongly. This tolerance problem is part of why researchers have looked at other strategies for sustaining nitric oxide levels over the long term.
Supplements on the market take a different approach. Instead of bypassing the body's natural pathway of nitric oxide production, they are intended to support it — supplying more of the raw materials out of which the body creates nitric oxide.
But the clinical results have not been as impressive as the marketing.
The Supplement Approach: L-Arginine and L-Citrulline
The most common ingredient in products marketed as "nitric oxide boosters" is L-arginine — an amino acid that is a key component of the primary pathway for nitric oxide production in the body [5].
Many human studies have examined L-arginine supplementation [6][7][8]. While L-arginine blood levels do rise, this has not reliably translated into athletic performance improvements or meaningfully raised nitric oxide levels.
L-citrulline is another option that has attracted research interest. It is converted to L-arginine after ingestion, and research has shown it is actually more effective than L-arginine itself at raising blood levels of L-arginine [9]. Could L-citrulline raise nitric oxide levels where L-arginine fell short?
The research has been underwhelming. A recent study tested L-citrulline in healthy young adults to see if it would increase time to exhaustion during exercise — it did not [10]. A 2019 meta-analysis did find that L-citrulline seems to slightly reduce blood pressure when the dose reaches at least 6 g/day [11], but the effect size is modest at best.
More recently, excitement has been building around nitrate supplements, which target a separately discovered pathway for supplying nitric oxide to cells.
The Nitrate Pathway: Beetroot Juice
Nitrate (with an 'a'), found naturally in foods like leafy greens, is converted into nitrite (with an 'i') by bacteria on the tongue, and further modified through digestion to eventually produce nitric oxide in the blood [12]. A popular supplement category targets this pathway using beet-derived products, since beets are rich in nitrate [13].
Clinical trials have produced encouraging results. A key 2014 study tested a daily dose of beetroot juice containing about 397 mg of nitrate against a placebo in patients with high blood pressure [14]. The beetroot juice significantly reduced blood pressure by around 8 points — an effect size comparable to blood pressure medication, which is meaningful for reducing the risk of strokes and heart attacks [14]. The study also found that beetroot juice improved blood vessel function by approximately 20% and reduced arterial stiffness [14].
Another study found that just one week of daily doses of beetroot juice containing 378 mg of nitrate significantly improved exercise endurance and blood pressure in elderly patients with heart failure [15].
However, beetroot products vary wildly in their nitrate content. Testing organisation ConsumerLab found that, among products tested, nitrate ranged from as much as approximately 500 mg to as little as 4.3 mg per serving — more than a 100-fold difference [16]. Beetroot powder supplements were particularly prone to having lower nitrate levels.
An analysis of 24 beetroot products found that only 5 contained a nitrate level of at least 300 mg per serving — the minimum level considered necessary for meaningful health effects [13].
That nitrate threshold cannot be delivered in a pill. Any supplement company selling a pill "nitric oxide booster" is providing, at best, a negligible dose of the active compound. To reach 300 mg of nitrate reliably, a liquid product like beetroot juice is needed — or the whole food itself.
Eating beets is generally preferable to an extract, since whole foods carry additional nutrients alongside the target compound. But beets come with a notable downside: they are among the highest food sources of oxalate [17]. Oxalate can inhibit the bioavailability of certain nutrients by binding to minerals and reducing their absorption [18], and it can contribute to kidney stones in susceptible individuals [17].
Tadalafil: A Different Kind of NO Booster
Tadalafil is an off-patent (and therefore inexpensive) pharmaceutical that takes a mechanistically distinct approach to the nitric oxide problem. Rather than adding nitrate from outside the body, it amplifies the signal that the body's existing nitric oxide is already sending.
Here is how it works: nitric oxide relaxes blood vessels by generating a messenger molecule called cGMP. The body produces an enzyme called PDE5 that degrades cGMP almost as quickly as it is made. Tadalafil blocks PDE5 — by preventing the breakdown of cGMP, it amplifies and prolongs the effects of the nitric oxide the body is already producing [19].
The medication was originally investigated as a treatment for cardiovascular conditions such as hypertension and angina, and has attracted attention because of eye-catching observational data. A study examining a large database of health records tracked outcomes for men prescribed tadalafil — or a similar PDE5 inhibitor — over 3 years. Compared with those not taking this drug class, tadalafil was associated with a 34% lower risk of death and a 27% lower risk of heart attack. Stroke risk was 34% lower and dementia risk fell by 32% [20].
A 2024 UK Biobank study reported similar findings: tadalafil was associated with a 28% reduced risk of death from all causes [21].
Importantly, these are observational studies. There is serious potential for healthy-user bias in this data. Tadalafil is most often prescribed for erectile dysfunction, and men who are prescribed it and continue taking it are, almost by definition, healthier than men with ED who go untreated. They are also engaged with the healthcare system, likely have better baseline cardiovascular function, and may have healthier lifestyles overall. Randomised controlled trial data is needed before conclusions about causation can be drawn — and that data does not yet exist. No current clinical guidelines recommend tadalafil for preventive cardiovascular care.
There are also important contraindications. Tadalafil can be dangerous in combination with nitrate medications like nitroglycerin or ISMN — the combination can cause a life-threatening drop in blood pressure [19]. Additionally, the actual effect of tadalafil on blood pressure is minimal — less than 1.5 mmHg and often less than 1.0 mmHg compared with placebo [22], which is a modest benefit for those primarily interested in blood pressure management.
Arugula: The Evidence-Based Whole-Food Alternative
Given the limitations of nitric oxide supplements and the oxalate drawback of beets, there is a whole-food alternative that the evidence strongly supports: arugula (also known as rocket).
Arugula is a natural food source of nitrates, just like beets — but unlike beets, it is low in oxalate [18]. More importantly, it is one of the highest-nitrate vegetables available, comfortably surpassing beets. A worldwide systematic review and meta-analysis of nitrate content in vegetables found that rocket (arugula) contains approximately 4,825 mg of nitrate per kg, compared with roughly 3,000 mg/kg for beetroot [23].
Running the numbers: at approximately 4.8 mg of nitrate per gram of arugula, hitting the evidence-based 300 mg threshold requires around 63 grams of arugula — roughly a medium salad. A simple preparation — arugula, olive oil, black pepper, and lemon juice — is a whole-foods approach to dietary nitrate that requires no supplements, no prescriptions, and no specialist products.
For most people, this is the most practical and evidence-backed strategy available for supporting the body's nitric oxide system: inexpensive, low-risk, and grounded in the same nitrate pathway that the beetroot juice research has validated. Arugula delivers more nitrate per gram than beetroot, without the oxalate burden, and requires no supplements, no prescriptions, and no specialist products.
The bottom line from the evidence: nitric oxide supplement pills are largely ineffective due to insufficient dosing and poor bioavailability. Beetroot juice in adequate doses (≥300 mg nitrate) does show meaningful effects on blood pressure and exercise capacity — but quality varies enormously between products. A daily arugula salad of approximately 63 g delivers the same nitrate dose in whole-food form, with a cleaner safety profile and at a fraction of the cost of commercial supplements.
References
1. https://pmc.ncbi.nlm.nih.gov/articles/PMC11504650
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC8348219/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC14594
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC4752190
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC9190231/
6. https://pubmed.ncbi.nlm.nih.gov/18708287/
7. https://jn.nutrition.org/article/S0022-3166%2822%2902486-5/fulltext
8. https://journals.physiology.org/doi/abs/10.1152/japplphysiol.00503.2010
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC2291275/
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC6369322/
13. https://pmc.ncbi.nlm.nih.gov/articles/PMC8512783/
14. https://pmc.ncbi.nlm.nih.gov/articles/PMC4288952/
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC4892939/
16. https://www.consumerlab.com/reviews/beetroot-nitrate-juice-powder-chew/beetroot/
17. https://www.imrpress.com/journal/FBL/8/6/10.2741/1082
18. https://pmc.ncbi.nlm.nih.gov/articles/PMC10486698/
19. https://www.ncbi.nlm.nih.gov/books/NBK603743/
20. https://www.amjmed.com/article/S0002-9343(24)00705-8/fulltext
21. https://onlinelibrary.wiley.com/doi/10.1111/acel.14334
22. https://pmc.ncbi.nlm.nih.gov/articles/PMC8845471/
23. https://www.sciencedirect.com/science/article/pii/S0147651323004384
