Short answer: No. Humans do not “use” the nitrogen in the air we breathe; it is largely inert in respiration and is exhaled without changing. Details
- What nitrogen does in breathing: The air we inhale is mostly nitrogen (~78%) and oxygen (~21%). The lungs absorb oxygen into the bloodstream to power metabolism, while nitrogen passes through the lungs largely unchanged and is expelled on exhalation. There is negligible metabolism or chemical uptake of nitrogen by human cells. This is why breathing pure nitrogen or very high-nitrogen mixtures can be dangerous (displacing oxygen) but nitrogen itself is not utilized in energy production or biomolecule synthesis in humans. [source context reflected in standard physiology and atmospheric composition understanding]
- Why we need nitrogen elsewhere: Although not metabolically used for energy, nitrogen is essential for building proteins, nucleic acids, and other biomolecules in our diet, because dietary nitrogen is incorporated into amino acids and nucleotides during digestion and metabolism. The nitrogen atoms in our body ultimately come from the nitrogen-containing molecules we ingest (primarily from plants and animal products that have assimilated nitrogen from the environment). In the atmosphere, nitrogen is abundant, but biological uptake happens after it is fixed into usable forms by bacteria and plants. [general biochemistry and ecology context]
If you want, I can tailor this explanation to a specific audience (high school biology, college physiology, or a quick one-page summary).
