Holistic Health Supplements The Health Benefits of L-Cysteine By Cathy Wong facebook twitter Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health. Learn about our editorial process Cathy Wong Medically reviewed by Medically reviewed by Arno Kroner, DAOM, LAc on December 06, 2020 facebook twitter linkedin Arno Kroner, DAOM, LAc, is a board-certified acupuncturist, as well as an herbalist and integrative medicine doctor. He operates a private practice in Santa Monica, California. Learn about our Medical Review Board Arno Kroner, DAOM, LAc on December 06, 2020 Print Table of Contents View All Table of Contents Health Benefits Possible Side Effects Dosage and Preparation What to Look For Other Questions L-cysteine is a semi-essential amino acid found naturally in the human body. Abundant in protein-rich foods, L-cysteine is also sold as a dietary supplement (sometimes just called cysteine). Along with the amino acids glutamine and glycine, cysteine is a building block of the powerful antioxidant glutathione. The body can make cysteine from the amino acids methionine and serine, but if these are in short supply, supplementing with L-cysteine can fill the gaps. Among the uses promoted for L-cysteine are the easing of flu symptoms, the treatment of certain inflammatory diseases, and the management of diabetes. Amarita / Getty Images Health Benefits In alternative medicine, L-cysteine is used as a natural treatment for: AnginaCardiovascular diseaseChronic bronchitisDiabetesFluInflammationInflammatory bowel diseaseOsteoarthritis In addition, it is said to enhance lung health in people with chronic obstructive pulmonary disease (COPD) and help prevent colon cancer, boost sports performance, and promote detox. But despite the many purported health uses for L-cysteine, research on the effects of supplementation is limited. A 2018 literature review published the journal Molecules noted the amino acid's effectiveness is still unclear and further research is needed. With that said, the amino acid shows at least some potential benefit for certain health conditions. Here's a look at several key findings from the available research. Diabetes Research suggests that L-cysteine may aid in the treatment of diabetes by lowering blood sugar, reducing insulin resistance, and preventing blood vessel damage. A 2012 literature review published in the Canadian Journal of Physiology and Pharmacology found that cysteine-rich whey protein improves glucose metabolism in people and animals with type 2 diabetes. However, the study authors note that more research is needed. An earlier study published in Free Radical Biology & Medicine found that diabetic rats treated with L-cysteine experienced a significant decrease in blood-sugar levels and insulin resistance. It also appeared to inhibit blood vessel inflammation, a key contributor to heart disease among those with diabetes. While the study was based on animals and not humans, the amino acid shows promise for those with diabetes. Type 2 Diabetes Colitis A 2009 study from the Dutch journal Biochimica et Biophysica Acta suggests that L-cysteine shows promise in the treatment of colitis, a type of inflammatory bowel disease. In tests on pigs, scientists found that L-cysteine may help reduce colitis-associated inflammation of the gastrointestinal tract. The Lifelong Management of Ulcerative Colitis Free Radicals L-cysteine may help prevent exercise-induced overproduction of free radicals, a process shown to contribute to oxidative stress. In an experiment involving 10 male basketball players, the authors of a 2007 study published in Clinical Chemistry and Laboratory Medicine determined that one week of supplementation with L-cysteine helped boost antioxidant capacity and reduce free radical production. It's too soon to recommend L-cysteine supplements as a treatment for any condition. It's important to note that self-treating a chronic condition—especially a serious illness such as COPD or cardiovascular disease—and avoiding or delaying the use of standard care can have serious health consequences. If you're considering the use of L-cysteine supplements, consult your physician first to weigh the potential risks and benefits. Possible Side Effects Although little is known about the safety of long-term use of L-cysteine supplements, there's some concern that taking L-cysteine in combination with certain medications—such as prednisone and other drugs that suppress the immune system—may increase the potency of those medications and trigger adverse effects. The safety of L-cysteine in pregnant women, nursing mothers, children, and those with medical conditions or who are taking medications has not been established. Dosage and Preparation L-cysteine is available as a dietary supplement in capsule and powder form. It is often found in protein powders, including whey- and plant-based proteins. There is no standard dosage. Follow the recommendations on the supplement label. What to Look For Widely available for purchase online, L-cysteine supplements are sold in many natural-foods stores, drugstores, and stores specializing in dietary supplements. Dietary supplements are largely unregulated. To ensure the safety and quality of any supplement, look for an independent third-party seal on the label, such as U.S. Pharmacopeia, NSF International, or ConsumerLab. The label should not make any health promises that it can treat or cure a disease, according to U.S. Food and Drug Administration (FDA) guidelines. Many L-cysteine supplements are made from chicken feathers. This may be of a concern to some, including those who are vegetarian/vegan or who follow a kosher diet. Some manufacturers take steps to remove the feathers using kosher methods, in which case the product label will contain the kosher symbol. Some protein powders and supplements contain L-cysteine derived from whey protein. Whey is dairy, so kosher rules regarding dairy apply to these products. Other Questions What foods contain L-cysteine?L-cysteine is found in many foods including meat, dairy products, eggs, nuts, seeds, and legumes. It is also abundant in protein powders used in weight-loss and body-building shakes and smoothies. I've heard NAC is a beneficial supplement. Is L-cysteine the same thing?N-acetyl-L-cysteine (NAC) is similar to, but not exactly the same as L-cysteine. Chemically speaking, NAC is an acetylated variant and precursor of the amino acid L-cysteine. While L-cysteine is found in many food sources, NAC is not; it is only available through supplementation. The purported health benefits of NAC are also different than the benefits of L-cysteine. NAC show promise for treating psychological disorders, such as obsessive compulsive disorder, addiction, and trichotillomania. Is it true that L-cysteine is made from human hair?L-cysteine is abundant in human hair and, in the past, supplement manufacturers extracted the amino acid from hair collected at barbers and salons. This is no longer common practice. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Penn State Hershey, Milton S. Hershey Medical Center. Cysteine. January 1, 2017. Clemente plaza N, Reig garcía-galbis M, Martínez-espinosa RM. Effects of the usage of l-cysteine (l-Cys) on human health. Molecules. 2018;23(3). doi:10.3390/molecules23030575 Jain SK. L-cysteine supplementation as an adjuvant therapy for type-2 diabetes. Can J Physiol Pharmacol. 2012;90(8):1061-4. doi:10.1139/y2012-087 Sansone RA, Sansone LA. Getting a knack for NAC: N-acetyl-cysteine. Innov Clin Neurosci. 2011;8(1):10–14. Additional Reading Clemente Plaza N, Reig García-Galbis M, Martínez-Espinosa RM. Effects of the Usage of l-Cysteine (l-Cys) on Human Health. Molecules. 2018;23(3). pii: E575. doi:10.3390/molecules23030575. Jain SK. L-cysteine supplementation as an adjuvant therapy for type-2 diabetes. Can J Physiol Pharmacol. 2012;90(8):1061-4. doi:10.1139/y2012-087.