L-cysteine: benefits, side effects and precautions


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

There is some evidence for the benefits of L-cysteine supplementation. This can help ease flu symptoms. It can also help treat some inflammatory conditions and help diabetics cope with the disease. This article explores the investigation of possible use cases, although these remain undefined.

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What is L-cysteine used for?

L-cysteine can be used as a natural treatment for conditions including:

L-cysteine may also support lung health in people with chronic obstructive pulmonary disease (COPD), help prevent colon cancer, improve athletic performance, and promote detoxification.

But despite the numerous claims about L-cysteine, there is still not extensive knowledge of the effects of its use. A 2018 review published in the journal Molecules notes that the amino acid's benefits are unclear and more research is needed .


L-cysteine is found in many foods that we eat. Pork chops, beef, chicken, and tuna are good sources. As well as oatmeal, eggs, and yogurt. Adding more pills and powders to your diet can provide health benefits, but scientists are still looking for evidence on the use of L-cysteine.


Research shows that L-cysteine can help treat diabetes by lowering blood sugar, reducing insulin resistance, and limiting blood vessel damage. This can be especially important for blacks who have higher levels of diabetes, heart disease, and a genetic type of enzyme deficiency that is more common in men. It's called G6PD for short and is associated with many complications .

A 2018 study published in the journal Diabetes found that L-cysteine helps make up for G6PD deficiency. High blood sugar levels can help reduce G6PD levels and blood and blood vessel related problems, but L-cysteine appears to restore these levels and improve function.

An earlier study published in the Canadian Journal of Physiology and Pharmacology found that cysteine-rich whey protein improves glucose metabolism in humans and animals with type 2 diabetes. However, the study authors noted that more is needed. investigation.

Free radicals

L-cysteine can help prevent the production of exercise-related free radicals, which have been shown to contribute to oxidative stress . It acts as an antioxidant .

However, as the Molecules authors pointed out, most of the clinical trials used to test L-cysteine have focused on the effects of a related derivative called N -acetyl-1-cysteine (NAC). Recently , there has been interest in how NAC can be used to treat people with COVID-19 .

It is important to know that NAC is not approved by the FDA as a dietary supplement. The FDA considers NAC to be a drug. The difference has sparked many years of controversy because the FDA bans the sale of NAC as a cure for everything from hangovers to Alzheimer's. It can also be confusing because L-cysteine itself is an approved supplement.

Possible side effects.

Little is known about the long-term safety of L-cysteine products. There is some concern that taking L-cysteine at the same time as other medications that suppress the immune system, such as prednisone, may increase the effects of these medications and cause negative effects.

The safety of L-cysteine in pregnant women, nursing mothers, and children is unknown.


It is too early to say that foods with L-cysteine can cure any disease. It's important to note that self-medication for a chronic problem, especially a serious medical condition like COPD or heart disease, while refusing or delaying a doctor's appointment can have serious health consequences. If you are considering using L-cysteine, first discuss the risks and benefits with your doctor.

Dosage and preparation

L-cysteine is available as a dietary supplement in capsules and as a powder. It is often found in protein powders, such as whey and plant proteins.

There is no standard dosage. Follow the directions on the product label.

What to look for

L-cysteine products, widely available for purchase online, are sold in many health food stores, drug stores, and supplement stores.

To ensure safety and quality, look for independent third-party prints on the label, such as NSF International or ConsumerLab. There should be no health promises on the label that it can treat or cure diseases as recommended by the FDA.

Many foods with L-cysteine come from chicken feathers. This may be of concern to some, including vegetarians, vegans, or those on a kosher diet. Some foods contain L-cysteine, derived from whey protein. Whey is milk based and therefore kosher rules apply.


Our bodies produce L-cysteine and healthy amounts are found in meats and other protein-rich foods. Adding supplements to these natural sources can help people with diabetes and other health problems, but the science is not over yet.

How L-cysteine and related amino acids can benefit health is being investigated. Be sure to discuss side effects, drug interactions, and other concerns with your doctor before adding L-cysteine to your diet.

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