An erection is a blood-flow event. So is genital arousal in women. Nitric oxide is the signal that tells the blood vessels involved to relax and let blood in, which is why nitric oxide and sexual health are so closely tied, and why a change in sexual response can be one of the earliest signs that your circulation needs attention. This guide covers how the mechanism works, what helps it, what the research on supplements actually shows, and when a change is worth a GP visit.
On this page
What nitric oxide does in your blood vessels
The thin lining of your blood vessels, the endothelium, makes nitric oxide from the amino acid L-arginine, using an enzyme called eNOS. Nitric oxide tells the smooth muscle in the vessel wall to relax, the vessel widens, and more blood flows through. It lasts only seconds, so your body has to keep making it.
How nitric oxide relaxes a blood vessel
The vessel's lining makes nitric oxide. It tells the muscle around it to relax, and the vessel widens.
Lining making plenty
- Muscle relaxed
- Wider channel
- More blood flows in
Lining making less
- Muscle stays tighter
- Narrower channel
- Less blood flows in
- Muscle layer
- Lining
- Nitric oxide
- Lining makes nitric oxide
- Wall muscle relaxes
- Vessel widens, blood flows in
Simplified diagram, not to scale.
How to read it. Same vessel, different amounts of nitric oxide from the lining. In the genitals, that widening is what lets the tissue fill with blood.
There is a second route. Nitrate from vegetables is turned into nitrite by bacteria on your tongue, and your body turns that nitrite into nitric oxide. It does not depend on the vessel lining, which matters as you get older.
What reduces nitric oxide is a familiar list: ageing, smoking, high blood pressure, diabetes, high cholesterol, sitting most of the day, and the oxidative stress that comes with all of them. Each one damages the lining or uses up the nitric oxide it makes. There is more on what nitric oxide does in the body and on signs your nitric oxide may be low in our other guides.
Two ways your body makes nitric oxide
Both end the same way: the muscle in the vessel wall relaxes and the vessel widens.
Route 1 From protein foods
- Arginine from nuts, seeds, legumes, meat and fish. Citrulline from watermelon, which the body turns into arginine.
- The lining of your blood vessels turns arginine into nitric oxide.
- The vessel relaxes and widens.
Helps: exercise. Faster blood flow along the lining is one of its main triggers.
Route 2 From vegetables
- Nitrate in rocket, silverbeet, spinach, beetroot and celery.
- Bacteria on your tongue turn nitrate into nitrite.
- Your body turns nitrite into nitric oxide.
- The vessel relaxes and widens.
Blocks: antibacterial mouthwash, which kills the tongue bacteria.
Helps: real beetroot or its juice, at the amounts the trials used.
How to read it. Follow each route from top to bottom. The tags show the everyday habits with evidence for helping or blocking that route. Sources: Burnett 2006, Kapil 2013.
How an erection works, and where nitric oxide fits
The sequence, in plain English
Sexual stimulation makes nerves in the penis release nitric oxide. Nitric oxide raises a messenger inside the muscle cells called cGMP, the smooth muscle relaxes, and the spongy tissue fills with blood. As it fills, it compresses the veins that would normally drain it, so the blood stays. An enzyme called PDE5 then breaks down cGMP, the muscle tightens, and the erection ends.
Prescription erectile dysfunction medicines act on that last step, by slowing PDE5, which bpac NZ explains for New Zealand doctors. They don't make nitric oxide. They let the nitric oxide you have work for longer, which is why they need the signal to be there in the first place.
Why age and health conditions matter
A lining that makes less nitric oxide is a leading physical cause of erection problems. New Zealand's Goodfellow Unit puts it plainly for GPs: erectile dysfunction and endothelial dysfunction are closely linked, and treating the erection without looking at the vessels misses the point. Diabetes is the clearest case, because it damages both the lining and the nerves that release nitric oxide, which is why diabetes and erectile dysfunction go together so often.
Nitric oxide isn't the only signal involved. A review titled "Gas what" makes the case that other pathways contribute too, so low nitric oxide is one of several possible causes rather than the whole story. A GP can work out which apply to you.
Nitric oxide and women's arousal
The same machinery exists in women. The enzyme that makes nitric oxide, eNOS, is found throughout the female genital tract, and during arousal nitric oxide increases blood flow to the clitoris and vagina. That blood flow drives engorgement, sensitivity and lubrication.
Here the evidence is thinner, and it's worth being plain about that. Most of it is mechanistic or from animal studies. A small 2011 pilot applied a nitric oxide-releasing gel and measured a change in clitoral blood flow, but no benefit to sexual function was shown. Women's sexual response is also strongly shaped by hormones, especially across menopause, by relationships, and by mental health. If arousal or comfort has changed around menopause, a GP or women's health clinician has more to offer than any article about nitric oxide.
What nitric oxide can't do: desire
Nitric oxide is about the physical response, not wanting it. Desire comes mostly from hormones (testosterone and oestrogen), stress, sleep, mood, how things are in the relationship, and medicines. Some antidepressants and some blood pressure tablets lower libido or affect erections, which Healthify NZ lists. If a change followed a new prescription, that is the first thing to raise with your doctor, and the answer is never to stop the medicine on your own.
So "does nitric oxide increase libido" has a short answer: not directly. If desire is the problem, blood flow is the wrong place to start.
Erection changes can be an early warning for your heart
This is the most useful thing on this page, and it reframes the whole topic. The arteries in the penis are narrow, about a third the width of the coronary arteries. When arteries start to narrow, the smallest ones show it first. That is the artery-size hypothesis, and the research behind it is consistent.
Why erection problems often come first
In a study of 300 men with confirmed coronary artery disease, two thirds of those who also had erectile dysfunction had developed it before any heart symptom, on average about three years earlier. In a JAMA study of 9,457 men aged 55 and over, men who developed erection problems had a 25% higher risk of a cardiovascular event over the following years, after adjusting for the usual risk factors. The authors' phrase was that erectile dysfunction is "a harbinger of cardiovascular clinical events in some men".
In research, erection problems often came first
300 men with confirmed coronary artery disease. In two out of three, erection problems came before any heart symptom.
-
Erection problems begin
The first sign, in 67% of the men.
-
About 3 years
average gap, range 1 month to 14 years
-
Heart symptoms appear
Chest pain, then a diagnosis of coronary artery disease.
Research finding, not a rule for any one person. Source: Montorsi et al, European Urology, 2003.
How to read it. The gap is the useful part. Three years is time to find high blood pressure, high cholesterol or diabetes early and do something about them. Source: Montorsi 2003.
The New Zealand numbers
A population survey of New Zealand men aged 40 to 70 found about 38% had erectile dysfunction once adjusted for age: 24% of men in their 40s, 38% in their 50s and 60% in their 60s. Only 16% of the men affected had a medical diagnosis, and only 22% had been treated. Most New Zealand men with this problem haven't told a doctor, and so haven't had the heart check that should come with it.
When to see your GP
The check itself is ordinary: blood pressure, cholesterol, blood sugar, and a conversation. Our guides to nitric oxide and blood pressure and practical ways to lower high blood pressure cover what to do with the results.
How to support nitric oxide naturally
The lifestyle evidence here is stronger than the supplement evidence, and it isn't close.
Move more
Aerobic exercise is one of the main triggers for the vessel lining to make nitric oxide. In a two-year randomised trial of 110 obese men with erectile dysfunction, the group given a diet and exercise programme improved their erectile function scores, and 17 of 55 regained normal function compared with 3 of 55 in the control group. A meta-analysis of six trials found the same direction: changing cardiovascular risk factors improved erectile function. Treat it as general health, not training for anything.
Stop smoking, keep alcohol moderate
Smoking damages the vessel lining and destroys nitric oxide directly, in proportion to how much you smoke. The damage can partly reverse after stopping. Heavy drinking raises blood pressure and blunts the response. Quitline is free in New Zealand.
Eat for your blood vessels
Two routes, two kinds of food. Nitrate-rich vegetables feed the second route, and arginine foods feed the first. A Mediterranean-style pattern, built on vegetables, legumes, nuts, fish and olive oil, is the best-studied eating pattern for erectile function, and a trial that added a daily handful of nuts to a Western diet found a modest improvement in healthy men.
| Food | What it gives you |
|---|---|
| Beetroot | Nitrate Roasted, grated raw into salad, or a 250ml glass of juice. |
| Silverbeet, spinach, rocket | Nitrate A big handful of rocket carries about as much nitrate as the juice used in trials. |
| Celery and lettuce | Nitrate Raw, in salads and sandwiches. Lettuce counts too. |
| Watermelon | Citrulline, which becomes arginine In season, as it is. The flesh near the rind has the most. |
| Walnuts, almonds, pumpkin seeds | Arginine A small handful a day. Nuts were the food tested in the one erectile function trial. |
| Lentils, chickpeas, beans | Arginine Through the week in soups, salads and curries. |
| Salmon, sardines, mussels | Arginine and omega-3 fats Two or three fish meals a week. Canned is fine. |
| Cocoa and dark chocolate | Flavanols that protect nitric oxide A couple of squares of 70% or more. It is a food, not a dose. |
| Kiwifruit, oranges, capsicum | Vitamin C, which protects nitric oxide One or two a day. Kiwifruit is the easiest in New Zealand. |
How to read this. Nitrate foods feed the second route, arginine foods the first, and the vitamin C and cocoa foods help the nitric oxide you make last longer. Rotate them; none is a dose. Sources: dietary patterns and erectile function, 2025; the FERTINUTS nut trial.
Beetroot and blood flow
Beetroot gets the attention because it works at food amounts. Across 16 trials, dietary nitrate and beetroot juice lowered systolic blood pressure by about 4.4 mmHg, and in a four-week trial in people with high blood pressure a daily 250ml glass of juice brought systolic pressure down by about 8 mmHg. The point is blood flow and blood pressure, not erections; no beetroot trial has measured those. And the effect needs real beetroot or its juice. Most beetroot powders deliver a fraction of the nitrate the trials used.
One habit works against the vegetable route. In a trial of 19 volunteers, a week of antibacterial mouthwash cut the mouth's nitrite production by 90% and raised blood pressure within a day. Keep it for when your dentist recommends it.
Sleep, stress and weight
Short sleep, chronic stress and extra weight all raise blood pressure and wear on the vessel lining. The blood pressure guide ranks them by how much each moves the number. Taurine has its own role in circulation, covered separately.
What the research says about nitric oxide supplements
This section is a literature summary. It is here because people search for it, and because the honest answer protects you from spending money on the wrong thing.
L-arginine
A 2019 meta-analysis of 10 randomised trials, 540 men with mild to moderate erectile dysfunction taking 1.5 to 5 grams a day, found an improvement compared with placebo. An earlier trial of 50 men found the improvement only in men who started with low nitric oxide markers, which fits the mechanism: if the lining is already making enough, more raw material does little. Much of swallowed arginine is broken down in the gut and liver before it reaches the circulation, which is why researchers turned to citrulline.
L-citrulline
The evidence is one small study. Cormio and colleagues gave 24 men with mild erectile dysfunction 1.5 grams a day for a month: 12 of 24 reported improved erection hardness on citrulline, against 2 of 24 on placebo. The weaknesses are real. It was single-blind, every man got placebo first, it wasn't randomised, and 24 men is 24 men. It is a reason for a bigger trial, not a result to buy on.
The big picture
A 2024 network meta-analysis pooled 15 randomised trials, about 1,000 men, across the supplements sold for erectile dysfunction. Its own summary was "a background of general ineffectiveness of most nutraceutical interventions". L-arginine showed some signal, mainly alongside prescription treatment in men with a physical cause.
Safety: who should be careful
Arginine, citrulline and hawthorn all affect blood vessels, so they can add to medicines that do the same.
- Nitrate heart medicines or prescription erectile dysfunction medicines. GTN spray, isosorbide, sildenafil and similar all lower blood pressure. Talk to your doctor before adding any nitric oxide supplement.
- Blood pressure medicines. Arginine and citrulline can add to their effect. Dizziness on standing is the sign.
- After a heart attack. A randomised trial of arginine after heart attack was stopped early because more people died in the arginine group. Avoid it unless your cardiologist agrees.
- Heart medicines generally. Hawthorn may interact with digoxin and some blood pressure medicines.
- Cold sores. Arginine may trigger outbreaks in people who get them.
- Pregnant or breastfeeding. Get advice first.
Supporting healthy circulation every day
We make a nitric oxide formula, and this is the one place in the article it appears, on purpose. Biosphere Nitric Oxide is built to support healthy circulation and blood flow, and to support healthy blood pressure, as part of a heart-healthy lifestyle. Each 6.5g scoop contains L-citrulline malate 2:1 2,000mg, L-arginine 1,000mg, taurine 500mg, hawthorn berry extract 500mg, vitamin C 300mg and vitamin D 200 IU, taken twice daily.
It's not magic, and it won't do what medication does. It's something to do alongside, aimed at the cause rather than the symptom.
Our co-founder Andrew on who it's for: people who want to improve their blood flow and support their own nitric oxide, most often older New Zealand men watching their blood pressure. Citrulline leads because it has the most evidence behind it. It's twice a day because nitric oxide doesn't hang around.
It's not a treatment for erectile dysfunction or any medical condition, and it's not a substitute for seeing your GP. If you take prescription medicines, check with your doctor first. Learn about Biosphere Nitric Oxide.
Frequently asked questions
What is the link between nitric oxide and sexual health?
Nitric oxide relaxes the smooth muscle in blood vessel walls so more blood can flow in. Erections, and clitoral and vaginal engorgement, depend on this. Anything that harms the vessel lining, such as smoking, diabetes, high blood pressure or inactivity, can reduce nitric oxide and affect sexual response.
Does low nitric oxide cause erectile dysfunction?
Reduced nitric oxide activity is one of the main physical mechanisms behind erectile dysfunction, usually because of blood vessel or nerve problems. But erectile dysfunction has many causes, including hormones, medicines, stress and relationship factors. A GP can work out which apply to you.
Can erectile dysfunction be a sign of heart disease?
Yes. Studies show erection problems often appear a few years before heart symptoms, because the arteries in the penis are small and show narrowing earlier. New erection problems are a good reason for a heart-health check with your GP.
Does nitric oxide increase libido?
Not directly. Nitric oxide affects the physical blood-flow response, not desire. Libido depends more on hormones, sleep, stress, mood, relationships and some medicines.
What foods boost nitric oxide?
Nitrate-rich vegetables (beetroot, silverbeet, spinach, rocket, celery), watermelon for citrulline, nuts, legumes, fish, cocoa, and vitamin C foods like kiwifruit and citrus. A Mediterranean-style diet is the best-studied eating pattern for blood vessel health.
Is beetroot good for blood flow?
Beetroot is high in dietary nitrate, which the body converts to nitric oxide. Trials show beetroot juice can modestly lower systolic blood pressure, which reflects improved blood vessel function. The effect comes from real beetroot or its juice, not a pinch of powder.
Does nitric oxide matter for women's arousal?
Yes. The same nitric oxide pathway helps increase blood flow to the clitoris and vagina during arousal. Women's sexual response is also strongly shaped by hormones, especially around menopause, and by emotional and relationship factors.
Are L-arginine and L-citrulline safe?
They're generally well tolerated at common doses, but they can lower blood pressure. Talk to your doctor first if you take blood pressure medicines, nitrate heart medicines or prescription erectile dysfunction medicines, have had a heart attack, or get cold sores.
When should I see a doctor about erection problems?
If they're new, getting worse, or happen alongside chest pain, breathlessness, diabetes or high blood pressure, or after starting a new medicine. Don't stop or change prescribed medicines without medical advice.
References
- Burnett AL. The role of nitric oxide in erectile dysfunction: implications for medical therapy. Journal of Clinical Hypertension, 2006. pmc.ncbi.nlm.nih.gov
- Kapil V, et al. Physiological role for nitrate-reducing oral bacteria in blood pressure control. Free Radical Biology and Medicine, 2013. doi.org
- bpac NZ. Erectile dysfunction. Best Practice Journal, April 2008. bpac.org.nz
- Goodfellow Unit. Erectile and endothelial dysfunction: thinking differently about treating ED. goodfellowunit.org
- Gas what: NO is not the only answer to sexual function. A review. pmc.ncbi.nlm.nih.gov
- Endothelial nitric oxide synthase regulation in female genital tract structures. pmc.ncbi.nlm.nih.gov
- Vascular modifications of the clitoris induced by topic nitric oxide donor gel: preliminary study. Journal of Sexual Medicine, 2011. academic.oup.com
- Healthify NZ. Medicines and sexual problems. healthify.nz
- Montorsi F, et al. Erectile dysfunction prevalence, time of onset and association with risk factors in 300 consecutive patients with acute chest pain and angiographically documented coronary artery disease. European Urology, 2003. europepmc.org
- Thompson IM, et al. Erectile dysfunction and subsequent cardiovascular disease. JAMA, 2005. jamanetwork.com
- Quilter M, Hodges L, von Hurst P, Borman B, Coad J. Male sexual function in New Zealand: a population-based cross-sectional survey of the prevalence of erectile dysfunction in men aged 40 to 70 years. Journal of Sexual Medicine, 2017. sciencedirect.com
- Healthify NZ. Erectile dysfunction. healthify.nz
- Esposito K, et al. Effect of lifestyle changes on erectile dysfunction in obese men: a randomized controlled trial. JAMA, 2004. jamanetwork.com
- Gupta BP, et al. The effect of lifestyle modification and cardiovascular risk factor reduction on erectile dysfunction: a systematic review and meta-analysis. Archives of Internal Medicine, 2011. jamanetwork.com
- Association between improved erectile function and dietary patterns: systematic review and meta-analysis. pmc.ncbi.nlm.nih.gov
- Effect of nut consumption on erectile and sexual function in healthy males: the FERTINUTS randomised controlled trial. pmc.ncbi.nlm.nih.gov
- Siervo M, et al. Inorganic nitrate and beetroot juice supplementation reduces blood pressure in adults: a systematic review and meta-analysis. Journal of Nutrition, 2013. pubmed.ncbi.nlm.nih.gov
- Kapil V, et al. Dietary nitrate provides sustained blood pressure lowering in hypertensive patients: a randomized, phase 2, double-blind, placebo-controlled study. Hypertension, 2015. pubmed.ncbi.nlm.nih.gov
- Rhim HC, et al. The potential role of arginine supplements on erectile dysfunction: a systemic review and meta-analysis. Journal of Sexual Medicine, 2019. pubmed.ncbi.nlm.nih.gov
- Chen J, et al. Effect of oral administration of high-dose nitric oxide donor L-arginine in men with organic erectile dysfunction. BJU International, 1999. europepmc.org
- Cormio L, et al. Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology, 2011. europepmc.org
- Nutraceutical interventions for erectile dysfunction: a systematic review and network meta-analysis. Journal of Sexual Medicine, 2024. academic.oup.com
- Schulman SP, et al. L-arginine therapy in acute myocardial infarction: the VINTAGE MI randomized clinical trial. JAMA, 2006. jamanetwork.com
- Mayo Clinic. L-arginine. mayoclinic.org
- National Center for Complementary and Integrative Health. Hawthorn. nccih.nih.gov
Last reviewed: 10 October 2026. Next review: October 2027.