Nitric oxide doesn’t give you energy the way caffeine or calories do, but it plays a real role in how efficiently your body produces and delivers energy. It’s a signaling molecule your body makes naturally, and it influences blood flow, oxygen delivery, and even how your cells generate fuel. When nitric oxide levels are low, fatigue is one of the first things people notice.
How Nitric Oxide Affects Your Energy
Nitric oxide works on energy through two main pathways, and they pull in opposite directions. First, it relaxes blood vessels, widening them so more oxygen-rich blood reaches your muscles and brain. More oxygen means your cells can produce more of the fuel they run on (ATP). Second, nitric oxide actually slows down part of the energy-production machinery inside your cells by competing with oxygen at the final step of mitochondrial respiration. At normal, low concentrations, this inhibition is mild and reversible, and it may help your body distribute oxygen more evenly across tissues rather than letting the most active cells hog it all.
Think of it less like a gas pedal and more like a traffic controller. Nitric oxide doesn’t create energy from nothing. It helps your body get the right amount of oxygen to the right places at the right time, which makes energy production smoother and more efficient. At higher concentrations, though, nitric oxide and its byproducts can irreversibly damage mitochondria, which is why balance matters.
What Happens When Nitric Oxide Is Low
Reduced nitric oxide levels are linked to chronic fatigue. Without enough of it, blood vessels can’t dilate properly, circulation drops, and your tissues receive less oxygen and fewer nutrients. The result is lower energy production at the cellular level. You may feel persistently tired even when you’re sleeping enough and eating well.
This connection showed up in Long Covid research. Italian scientists found that many Long Covid patients who experienced disabling exhaustion had an alteration in arginine metabolism. Arginine is the amino acid your body uses to make nitric oxide. When arginine is depleted, nitric oxide production falls, impairing both immune and vascular function. Low nitric oxide has also been associated with depression and elevated blood pressure, both of which compound the feeling of low energy.
The Exercise Performance Connection
Where nitric oxide’s energy effects show up most clearly is during physical activity. When you exercise, your muscles demand far more oxygen than at rest. Nitric oxide triggers vasodilation, the widening of blood vessels, to increase blood flow and match oxygen delivery to that demand. This is why nitric oxide boosters have become popular in sports nutrition.
The research on beetroot juice, which is high in nitrates your body converts to nitric oxide, shows measurable performance gains. Trained cyclists who supplemented with beetroot juice improved their time-to-exhaustion at high intensity by as much as 16%. In time trials, completion times dropped by roughly 2.7% to 2.8%, with power output improving alongside. At moderate intensities (60% to 80% of max capacity), supplemented athletes consistently lasted longer before exhaustion, sometimes by nearly two minutes. In competitive sports, even a 0.5% to 1.5% improvement is considered meaningful, so these numbers are substantial.
L-citrulline, another common nitric oxide booster, produced some of the most striking results for cellular energy. One study using magnetic resonance spectroscopy found that 6 grams per day of citrulline malate for about 16 days increased the oxidative rate of ATP production during exercise by roughly 34%, with a 20% faster recovery of the phosphocreatine system afterward. That’s a direct measurement of your cells making more energy, more efficiently.
Nitric Oxide and Mental Energy
Your brain consumes about 20% of your body’s oxygen despite being only 2% of your body weight, so blood flow matters enormously for mental sharpness. Nitric oxide is synthesized in the brain and plays a role in cortical arousal, learning, and memory. By relaxing blood vessels in the brain, it increases the delivery of oxygen and glucose that neurons need to fire.
Animal studies have consistently shown that nitric oxide supports cognitive function. When nitric oxide activity in the brain is impaired, whether from stress, diabetes, epilepsy, or aging, learning and memory suffer. Supplementing with arginine or nitric oxide donors has reversed some of these impairments in research settings. In Alzheimer’s disease, where toxic protein deposits disrupt brain function, arginine supplementation has shown potential for reducing cognitive decline. So while “mental energy” is harder to measure than physical performance, nitric oxide’s role in keeping your brain well-supplied with blood is well established.
L-Citrulline vs. L-Arginine
Both amino acids boost nitric oxide, but they aren’t equally effective. L-arginine is the direct precursor your body uses to make nitric oxide, which makes it seem like the obvious choice. The problem is that when you take arginine orally, enzymes in your gut and liver break down a large portion of it before it ever reaches your bloodstream. This presystemic elimination significantly limits how much actually becomes available for nitric oxide production.
L-citrulline takes a detour that turns out to be more efficient. Your body absorbs it readily, then converts it into arginine in the kidneys, bypassing that gut-and-liver bottleneck. In a pharmacokinetic study published in the British Journal of Clinical Pharmacology, oral citrulline raised plasma arginine levels more effectively than arginine itself at every dose tested. At 3 grams twice daily, citrulline was the only treatment that significantly increased urinary nitrate excretion, a marker of actual nitric oxide production in the body. It also improved the ratio of arginine to its natural inhibitor (ADMA) from 186 to 278, a roughly 50% improvement in the body’s capacity to generate nitric oxide.
Practical Dosing and Side Effects
Most of the exercise studies showing benefits used 6 grams per day of either L-arginine or L-citrulline malate. At that dose, arginine supplementation for just three days (combined with vitamins and amino acids) extended time to exhaustion during cycling from about 562 seconds to 707 seconds. In older adults, 5.2 grams per day of arginine with citrulline and antioxidants for three weeks increased cycling power output by about 21%. Strength gains have been documented too: 6 grams of arginine daily for 56 days improved one-rep max bench press and peak anaerobic power.
For food-based approaches, beetroot juice is the most studied option. Most trials used concentrated shots containing around 6 to 8 mmol of nitrate, typically consumed two to three hours before exercise.
Side effects from arginine and citrulline supplements are generally mild but real. They can include nausea, bloating, diarrhea, stomach pain, headache, and occasionally palpitations. Tolerance varies widely between people, and doses above 9 grams per day increase the likelihood of gastrointestinal issues. Splitting doses into smaller amounts taken throughout the day tends to reduce these problems.
The Bottom Line on Energy
Nitric oxide doesn’t give you energy in the way a cup of coffee does, by stimulating your nervous system. It works underneath that, at the level of circulation and cellular metabolism. By improving blood flow and oxygen delivery, it helps your body produce energy more efficiently, particularly during physical and mental exertion. The people most likely to notice a difference are those who exercise regularly, those with poor circulation, or those whose nitric oxide levels have declined due to aging, stress, or chronic illness. For the average person eating a diet rich in leafy greens and beets, nitric oxide levels are typically adequate. Supplementation offers the most noticeable benefit when there’s a gap to fill or a performance edge to gain.