Characteristics: L-cysteine is a non-essential (conditionally essential) antioxidant amino acid that strengthens lung and brain function. The human body can usually make it from the amino acids, serine and methionine, but it needs enough folate, vitamin B6 and vitamin B12 to do this. L-cysteine is an important source of sulfur in human metabolism, and although it is classified as a non-essential amino acid, it may be essential for infants, the elderly, and individuals with metabolic disease. Along with two other amino acids, glutamine and glycine, L-cysteine is needed to make glutathione, a major antioxidant essential to human health. Supplementation with L-cysteine therefore increases the level of glutathione in the body, which is extremely important for the function of the lungs, the brain, and the detoxification of xenobiotics (foreign substances, drugs, poisons) in the liver. L-cysteine has the ability to dissolve mucus, making it easier to cough it up. In addition, it is involved in the regulation of the level of glutamate, the most important neurotransmitter in the central nervous system, and the formation of keratin, which is an essential part of our hair and nails.

Absorption: L-cysteine is transported by energy-dependent, mediated processes in the human intestine.

Dietary supplements: It is usually in the form of N-acetyl-L-cysteine (NAC). The body converts it to cysteine and then glutathione, a powerful antioxidant.

Natural sources: Many high-protein foods contain L-cysteine, although usually in small amounts. These foods include: chicken, turkey, duck, pork, yogurt, cheese, whey, eggs, sunflower seeds, legumes, oat bran, onions, garlic, and broccoli. The body makes L-cysteine from the amino acids serine and methionine, but it needs sufficient amounts of folate, vitamin B6, and vitamin B12 to do this.

Effect: L-cysteine acts as a scavenger of free radicals that cause cell damage through oxidative stress. Thanks to this, it can slow down the aging process and help prevent or treat several diseases. It supports immune function by increasing glutathione levels. Its thiol group (containing sulfur) has a high affinity for heavy metals; therefore it plays a key role in detoxification mechanisms in the body. It is recommended as an additional treatment for impotence in men or those with poor sperm quality. L-cysteine is also beneficial by helping to support the body's natural ability to manage and regulate normal blood sugar levels. NAC acts as an expectorant (clears coughs, thins mucus). In a clinical evaluation, the reduction of hair loss and its strengthening was confirmed due to the ability of L-cysteine to form disulfide bridges, which give keratin strength and rigidity.

Deficiency: L-cysteine deficiency is manifested by impaired antioxidant defenses, reduced ability to metabolize drugs or toxic compounds, and reduced immune function.

Recommended daily dose: Not defined.

Side Effects: Mild side effects include dry mouth, headache, dizziness, nausea, and vomiting.

Interactions: L-cysteine may interact with diabetes medications because blood sugar levels may drop too much.

Pregnancy: L-cysteine is commonly consumed in food. However, there is not enough reliable information about whether it is safe to use in large amounts during pregnancy.

Breastfeeding: L-cysteine is commonly consumed in food. However, there is not enough reliable information about whether it is safe to use in large amounts while breastfeeding.

Toxicity: Very high doses (more than 7 g) of L-cysteine can be toxic to human cells.


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