Semi-essential (conditionally essential) amino acids can be formed from other amino acids in the body. For example, the synthesis of cysteine is partially possible from the essential (necessary for life) amino acid methionine, and tyrosine can be formed from the essential amino acid phenylalanine.
Under certain conditions – e.g., age, growth phase, illness, or physical activity – semi-essential amino acids can become essential to the body.
In newborns, for example, arginine, cysteine, histidine and tyrosine are essential amino acids during the first days of life.
For children, tyrosine is essential in addition to the essential amino acids, since at this age the body’s own production from phenylalanine is not yet possible.
Conditionally essential amino acids include:
- Arginine*
- Asparagine*
- Cysteine
- Glutamine*
- Glycine*
- Proline*
- Tyrosine
If the body lacks an amino acid or an endogenous agent formed from it, such as a hormone, is no longer sufficiently produced, important body functions are no longer optimally ensured.
* These amino acids are specified in other literature as non-essential.
