The Benefits of Taking L-Cysteine

Milk eggs and legumes on a table have l-cysteine in them

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L-cysteine is an amino acid commonly sold in dietary supplement form. Also found naturally in the human body, L-cysteine is available in many foods as well. Use of L-cysteine supplements is said to offer a variety of health benefits.


In alternative medicine, L-cysteine is touted as a natural treatment for the following health problems:

In addition, L-cysteine is said to enhance lung health in people with chronic obstructive pulmonary disease (COPD), the third leading cause of death in the United States.

Some proponents claim that L-cysteine can also help prevent colon cancer, boost sports performance, and promote detox.

Health Benefits

So far, research on the health effects of taking L-cysteine supplements is limited. However, there's some evidence that L-cysteine may offer certain health benefits. Here's a look at several key findings from the available research:

1) Diabetes

Animal-based research indicates that L-cysteine may aid in the treatment of diabetes. In a 2009 study published in Free Radical Biology & Medicine, for instance, diabetic rats treated with L-cysteine experienced a significant decrease in blood sugar levels and in insulin resistance. Additionally, L-cysteine appeared to inhibit blood vessel inflammation (shown to be a key contributor to heart disease among diabetes patients).

2) 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.

3) 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.

Food Sources

There are a number of foods that contain L-cysteine, including meat, dairy products, eggs, and legumes.


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.

Supplements haven't been tested for safety and due to the fact that dietary supplements are largely unregulated, the content of some products may differ from what is specified on the product label. Also keep in mind that the safety of supplements in pregnant women, nursing mothers, children, and those with medical conditions or who are taking medications has not been established.

Where to Find It

Widely available for purchase online, L-cysteine supplements are sold in many natural-foods stores, drugstores, and stores specializing in dietary supplements.

Using It for Health

Due to the limited research, 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.

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