TL;DR:

Nitric oxide (NO) helps your blood vessels relax and improves circulation. It’s made in the lining of your arteries from arginine and citrulline, and is important for blood pressure, heart health, exercise performance, and even male vitality.

Human Growth Hormone (HGH) and Nitric Oxide.

What Is Nitric Oxide (NO)?

NO (nitric oxide) is a natural gas molecule produced by the endothelial cells — the cells lining your blood vessels.
Its job? To tell the smooth muscles around your arteries to relax, allowing blood to flow more easily.

Low NO means tight, stiff arteries — and that can lead to high blood pressure, poor circulation, and fatigue.
Your body makes NO from arginine, an amino acid found in foods like nuts, seeds, meat, and legumes. Citrulline can boost NO even more when combined with arginine.

NO and Blood Pressure

Reduced nitric oxide is common in conditions such as:

  • Chronic kidney disease
  • Diabetes and insulin resistance
  • Obesity
  • Aging

All of these are risk factors for resistant hypertension — blood pressure that doesn’t respond well to medication.

A meta-analysis (1) looked at 12 studies involving 492 people. It found that arginine supplementation increased flow-mediated dilation (FMD) — a measure of how well arteries widen when blood flow increases.
This widening is driven by nitric oxide release from the vessel walls.

Another study [2] found that a single oral dose of a nitric oxide supplement could lower blood pressure and improve vascular flexibility within hours.

Performance and Energy

Nitric oxide doesn’t just help the heart — it also boosts stamina.
A study in Aging [3] showed that arginine + citrulline supplementation in healthy older adults:

  • Lowered resting blood pressure
  • Improved cycling endurance
  • Enhanced oxygen use and recovery

In other words, more nitric oxide means better circulation and performance — even as we age.

Circulation and Peripheral Arteries

People with intermittent claudication — pain in the legs from poor circulation — may also benefit.
Researchers found that restoring nitric oxide with L-arginine improved walking ability and reduced leg pain [4].
Similar improvements in blood flow were seen in patients with heart failure [5].

Male Health and Vitality

Nitric oxide also supports erectile function by improving blood flow.
Research shows that arginine supplementation increases NO and can help men with mild erectile dysfunction (Future Sci OA, 2015).

Takeaway

Nitric oxide is your body’s natural vasodilator — it relaxes blood vessels, lowers pressure, and boosts performance.
Simple ways to support healthy NO levels include:

  • Eating arginine- and citrulline-rich foods (pumpkin seeds, watermelon, nuts, legumes)
  • Staying active and maintaining healthy weight
  • Arginine + citrulline supplements may help boost NO.

References:

  1.  Am J Clin Nutr  2009 Jan;89(1):77-84 Increase in fasting vascular endothelial function after short-term oral L-arginine is effective when baseline flow-mediated dilation is low: a meta-analysis of randomized controlled trials.
  2. J Clin Hypertens (Greenwich) 2014 Jul;16(7):524-9 Acute effects of an oral nitric oxide supplement on blood pressure, endothelial function, and vascular compliance in hypertensive patients
  3. Aging (Albany NY)   2019 May 29;11(10):3315-3332 Effect of chronic nitrate and citrulline supplementation on vascular function and exercise performance in older individuals
  4. J Am Coll Cardiol. 1998 Nov;32(5): 1336-44 Restoring vascular nitric oxide formation by L-arginine improves the symptoms of intermittent claudication in patients with peripheral arterial occlusive disease
  5. Eur J Appl Physiol 2016 Sep;116(9):1651-61. Oral nitrate and citrulline decrease blood pressure and increase vascular conductance in young adults: a potential therapy for heart failure
  6. Future Sci OA. 2015 Aug; 1(1): FSO53. Development and therapeutic applications of nitric oxide releasing materials to treat erectile dysfunction