Cathy Wong is a nutritionist and health expert. Her work often appears in media such as First For Women, Woman's World and Natural Health.

Richard N. Fogoros, MD, is a retired medical professor and a board-certified physician and cardiologist.

L-cysteine ​​is an amino acid naturally present in the human body. It is one of the amino acids that form part of the powerful antioxidant glutathione. It is also found in many protein-rich foods and sold as a dietary supplement.

There is some evidence of the benefits of L-cysteine ​​supplements. It may help relieve flu symptoms, treat some inflammatory diseases, and help diabetic patients control their condition.

This article looks at the research behind the possible uses, although the benefits are still uncertain.

L-cysteine ​​can be used as a natural treatment for the following conditions:

L-cysteine ​​can also support the lung health of patients with chronic obstructive pulmonary disease (COPD), help prevent colon cancer, and improve athletic performance.

However, despite many claims about L-cysteine, there is still not much knowledge about the effects of using it. A review published in the journal Molecule in 2018 pointed out that the benefits of amino acids are still unclear and further research is needed.

L-cysteine ​​is found in many foods we eat. Pork chops, beef, chicken and tuna are all good sources. The same goes for oatmeal, eggs and yogurt. Adding more to your diet through pills and powders may bring health benefits, but scientists are still studying the evidence for the use of L-cysteine.

Studies have shown that L-cysteine ​​may help diabetes management because it can lower blood sugar, lower insulin resistance and reduce blood vessel damage. This is especially important for people with heart disease or genetic enzyme deficiencies that are more common in men. It is called G6PD for short and is associated with many complications.

A study published in the journal Diabetes in 2018 found that L-cysteine ​​helps counteract G6PD deficiency. High blood sugar can cause low G6PD levels and related blood and vascular problems, but L-cysteine ​​seems to restore these levels and improve function.

An early study published in the Canadian Journal of Physiology and Pharmacology found that cysteine-rich whey protein can improve glucose metabolism in patients with type 2 diabetes and animals. However, the study authors pointed out that more research is needed before widespread recommendation.

L-cysteine ​​may help prevent the production of free radicals associated with exercise, which can cause oxidative stress and damage cells. Amino acids act as antioxidants.

However, most clinical trials used to test L-cysteine ​​have focused on the effects of a related compound called N-acetyl-l-cysteine ​​(NAC). Some people are even interested in how to use NAC to help treat COVID-19 patients.

It is important to know that NAC is not approved by the Food and Drug Administration as a dietary supplement. The FDA considers NAC to be a drug.

This difference has caused controversy for many years because the FDA banned the sale of NAC as a drug for treating all diseases from hangovers to Alzheimer's disease. It can also be confusing because L-cysteine ​​itself is an approved supplement.

Little is known about the safety of long-term L-cysteine ​​products. Some people worry that taking L-cysteine ​​and other drugs that suppress the immune system (such as prednisone) at the same time may increase the efficacy of these drugs and cause negative effects.

The safety of L-cysteine ​​in pregnant women, breastfeeding mothers and children is unclear.

It is too early to say that L-cysteine ​​products can treat any health condition. It should be noted that self-treatment of chronic problems—especially serious diseases such as chronic obstructive pulmonary disease or heart disease—while avoiding or delaying medical treatment may have serious health effects. If you are considering using L-cysteine, please discuss the risks and benefits with your doctor first.

L-cysteine ​​can be used as a dietary supplement in capsule and powder form. It is usually found in protein powders, including whey protein and vegetable protein.

There is no standard dose. Please follow the guidelines on the product label.

L-cysteine ​​products are sold in many natural food stores, pharmacies, and dietary supplement specialty stores, and can be widely purchased online.

To ensure safety and quality, please look for an independent third-party seal on the label, such as NSF International or ConsumerLab. According to FDA guidelines, the label should not make any health promises that can treat or cure diseases.

Many L-cysteine ​​products are made from chicken feathers. This may cause concern for some people, including vegetarians, vegans, or those who follow a Kosher diet. Some products contain L-cysteine ​​derived from whey protein. Whey is a dairy product, so the kosher rules regarding dairy products apply to them.

Our body makes L-cysteine, and meat and other high-protein foods also contain healthy L-cysteine. Adding these naturally-sourced supplements may help people with diabetes and other health problems, but science has not yet determined.

Continue to study how L-cysteine ​​and related amino acids provide health benefits. Before adding L-cysteine ​​to your diet, be sure to discuss side effects, drug interactions, and other issues with your doctor.

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Richardson SR, O'Malley GF. Glucose 6-phosphate dehydrogenase deficiency. In: StatPearls. Published by StatPearls; 2021.

Parsanathan R, Jain SK. The protective effect of l-cysteine ​​on high glucose induces g6pd deficiency and endothelial dysfunction. diabetes. 2018; 67 (Supplement 1): 474-P. doi: 10.2337/db18-474-P

Jain SK. L-cysteine ​​supplements are used as an adjuvant treatment for type 2 diabetes. Can J Physiol Pharmacol. 2012;90(8):1061-1064. doi:10.1139/y2012-087

Pizzino G, Irrera N, Cucinotta M, etc. Oxidative stress: harm and benefits to human health. Oxidative medicine and cell longevity. 2017; 2017: e8416763. doi: 10.1155/2017/8416763

Shi Z, Puyo CA. N-acetylcysteine ​​against COVID-19: a review of the evidence. Clinical risk management. 2020; 16:1047-1055. Published on November 2, 2020. doi:10.2147/TCRM.S273700

Food and Drug Administration. Unproven Alzheimer's disease product. December 22, 2018.

Jain S. L-cysteine ​​supplementation increases blood levels of hydrogen sulfide and nitrite, and reduces insulin resistance and vascular inflammation in zucker diabetic rats. Current developments in nutrition. 2020;4(Supplement_2):405-405. doi: 10.1093/cdn/nzaa045_038

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