What Is L-cysteine? 7 L-cysteine Benefits + L-cysteine Foods

What Is L-cysteine? 

L-cysteine is classified as a “semi-essential” amino acid because it can be made in small amounts by the human body, but many people can still benefit from consuming more cysteine from their diets or supplements because of its numerous health benefits. The human body can usually manufacturer L-cysteine from the amino acids serine and methionine, but you need enough folate, vitamin B6 and vitamin B12 for that to be possible.


Along with two other amino acids, glutamine and glycine, L-cysteine is needed to make glutathione, the master antioxidant that’s crucial for your health. L-cysteine is usually the amino acid that’s in shortest supply for making glutamine, so it’s important that you get enough of this amino acid, even though it’s not considered essential.


Although L-cysteine is a minor scavenger of oxidative stress, its most important role is reviving glutathione, one of the most powerful antioxidants in the body. Longevity researchers believe that glutathione is so pivotal to your health that the level of this antioxidant in your cells may be a predictor for how long you will live. It’s the body’s most important antioxidant because it is within the cell, making it essential for maintaining a healthy immune system and fighting cellular damage. (2)