Nitrogen is fundamental to all life on Earth. Although the air we breathe is about 78% nitrogen, humans cannot directly use it from the atmosphere. Instead, our bodies must obtain nitrogen through food. This element plays an indispensable role in the human body, forming the backbone of molecules essential for growth, repair, and numerous biological processes.
Nitrogen’s Essential Role in Human Biology
Nitrogen is a core ingredient of amino acids, the building blocks of proteins. Each amino acid contains an amine group, a chemical structure with nitrogen. Proteins, assembled from these amino acid chains, perform diverse functions throughout the body.
Some proteins provide structural support, forming components of muscles, hair, nails, and skin; collagen is a prominent example, giving strength and elasticity to tissues. Other proteins act as enzymes, accelerating metabolic reactions in digestion, energy production, and cellular processes. Proteins also function as hormones, coordinating activities across body systems, and as antibodies, protecting the body from foreign invaders. Transport proteins, like hemoglobin, carry substances such as oxygen throughout the bloodstream.
Beyond proteins, nitrogen is a fundamental component of nucleic acids, specifically DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). These molecules are composed of nucleotides: a sugar, a phosphate group, and a nitrogenous base. The nitrogenous bases—adenine (A), guanine (G), cytosine (C), and thymine (T) in DNA, or uracil (U) in RNA—are responsible for genetic coding and diversity.
The arrangement of these nitrogenous bases forms the genetic code, providing instructions for cellular activities, including protein synthesis. DNA carries genetic information, while RNA is involved in converting this genetic code into proteins. Nitrogen is also present in other molecules, such as adenosine triphosphate (ATP), the body’s primary energy currency, and certain vitamins like B12.
Acquiring Nitrogen for Bodily Needs
Humans obtain nitrogen for these biological functions primarily through diet. Protein-rich foods are the main sources of nitrogen, providing the amino acids our bodies need. Dietary sources include animal products like meat, fish, eggs, and dairy, as well as plant-based options such as legumes, nuts, and seeds.
The body cannot synthesize all 20 types of amino acids it needs; nine are “essential” and must be obtained from food. When we consume proteins, our digestive system breaks them down into individual amino acids, which are absorbed and utilized to build new proteins and other nitrogen-containing molecules.
While humans cannot directly absorb atmospheric nitrogen, plants play a crucial role in making it available to us. Certain soil bacteria convert atmospheric nitrogen gas into usable forms like ammonium and nitrates through nitrogen fixation. Plants absorb these nitrogen compounds from the soil, incorporating them into their proteins and other organic molecules. When humans consume these plants, or animals that have eaten them, nitrogen enters our food chain.
Consequences of Nitrogen Imbalance
Maintaining adequate nitrogen balance is important for overall health; imbalances can lead to adverse effects. Insufficient nitrogen intake, typically from a lack of dietary protein, can result in protein deficiency.
Symptoms of protein deficiency include muscle wasting, weakness, impaired growth (particularly in children), and a weakened immune system, increasing susceptibility to infections. Fluid retention, such as swelling (edema) in the feet and abdomen, can also occur because proteins help maintain fluid balance in blood vessels. Other signs include brittle hair and nails, dry skin, fatigue, and mood changes. Severe protein deficiency can lead to conditions like Kwashiorkor, characterized by significant swelling and health complications.
Conversely, excessive nitrogen intake, often from very high protein diets, can pose risks, though less common in healthy individuals. The body processes excess amino acids by converting their nitrogen into ammonia, a toxic substance. The liver converts this ammonia into urea, a less harmful compound, which is excreted by the kidneys in urine. An overload of nitrogen can strain the liver and kidneys as they work to eliminate urea. In cases of impaired kidney or liver function, the body’s ability to convert ammonia to urea can be compromised, leading to ammonia buildup in the bloodstream. High ammonia levels can be harmful, affecting neurological function and potentially leading to liver damage.