Overview
The human body converts nitrate to nitric oxide (NO), which is a signaling molecule associated with several physiological functions involving blood pressure regulation, cardiovascular health, mitochondria production, calcium transport, oxidative stress, and skeletal muscle repair.[1] It plays a prominent role as a vasodilator, which means it relaxes blood vessels and improves blood flow.
Nitrate supplementation, whether in its pure form (e.g. sodium/potassium nitrate), or via foods (e.g. beetroot juice/powder), may temporarily reduce the body’s oxygen demand during exercise. A decrease in oxygen demand may result in improved exercise and muscular performance.[2][3]
How are nitric oxide levels assessed?
Direct
The most accurate method of assessing NO levels is to measure plasma nitrate and nitrite in your blood. The half-life of NO is incredibly short, existing for less than 0.1 seconds before it breaks down into nitrate and nitrite.[4][5] These two metabolites are measured as stand-in measures (i.e., surrogate markers) of NO production.
Researchers may not use this method due to inconvenience or cost concerns. Instead, they may opt to use indirect approaches.
Indirect
It is not uncommon for researchers to test the effects of a nitrate-rich supplement on secondary endpoints affected by NO levels. Below is a list of frequently used endpoints.
Heart stroke volume | Speed | |
Cardiac output | Max effort | |
Time trials | ||
Graded exercise tests | Open-ended exercise tests | |
VO2peak |
What affects nitric oxide levels?
Supplements
NO levels can be increased through direct nitrate ingestion. Obvious, right? But there’s a twist — nitrates do not exist as isolated dietary supplements due to the regulations surrounding high quantities of sodium nitrate. Instead, nitrate supplementation is typically achieved via nitrate-rich foods or beverages. Most studies deliver nitrates in the form of beetroot juice or powder.
Supplements like citrulline and arginine may also boost NO levels, but their overall effect is moderate to minor.[6] Plant isoflavones, such as soy isoflavones, may also influence NO production.
The table below displays an analysis of human studies and indicates how supplements may affect NO levels and production.
Food
Nitrates are found in various foods, notably beetroot and leafy green vegetables. Beetroot extract capsules do not provide enough nitrates to affect blood flow, but beetroot powder and juice are valid options.
Arugula/rocket, collard greens, dill, and turnip greens also have a high nitrate content.[7][8]
Hormones
Estrogen regulates blood flow by inducing the production of NO,[9] a potent vasodilator made by endothelial cells, which is a specialized cell type lining all blood vessels. After being produced in the endothelium, NO diffuses into the underlying smooth muscle cells that regulate vascular tone, causing them to relax and subsequently increase blood flow through the body. This process is called vasodilation.
