L-cysteine: Benefits, Dosage, Side Effects, Foods (Science Based)
L-cysteine is an amino acid which is also sold as a dietary supplement. The benefits of L-cysteine are mostly due to the fact that it’s one of the building blocks of glutathione – one of the body’s main antioxidants. Scientific studies have shown that L-cysteine can help improve digestion, boost mental health, reduce pain, and help rid your body of toxins.
L-cysteine could also help you lose weight, reduce inflammation, and boost cardiovascular health. Many people take L-cysteine supplements because their benefits are experienced with very few side effects.
L-cysteine supplementation, is also available as a NAC supplement (also known as N-acetyl-L-cysteine).
In this article, you will learn about many of the benefits of L-cysteine. You will also find out how to take L-cysteine supplements to boost your health in general.
What is L-cysteine?
L-cysteine is an important amino acid that is required by your body in order to produce the antioxidant glutathione, “the mother of all antioxidants.”
N-acetyl-L-cysteine (NAC) is a precursor of L-cysteine and as such, you can take NAC supplements to boost cysteine levels.
In a review on the effects of N-Acetyl Cysteine (NAC), researchers said that NAC is a precursor of L-cysteine. The increase of L-cysteine then elevates levels of glutathione. This is an important antioxidant that destroys free radicals in the body and prevents oxidative stress. (1)
The journal Innovations in Clinical Neuroscience said that reducing oxidative stress benefits mental health and can prevent psychiatric disorders. Researchers described N-Acetylcysteine as an essential element of the immune system. (2)
L-cysteine supplements are available as 400 mg tablets, 500 mg capsules and tablets, or 600 mg capsules. N-Acetyl-L-cysteine (NAC) is also available as a powder in packs between 100 g and 1 kg.
L-Cysteine Overview: Benefits and Side Effects
Here is a brief overview of the many ways that L-cysteine supplements can benefit your health and prevent disease.
L-cysteine acts as a scavenger for free radicals in the body because it directly increases levels of glutathione. The activity of free radicals in your body is linked to chronic diseases, premature aging, and even cancer.
L-cysteine supplements improve mental health. There is medical research pointing to the fact that they can reduce the severity of psychiatric disorders. Some of these include depression, bipolar disorder, and OCD.
Some studies have also shown that L-cysteine supplements could reduce the symptoms of Alzheimer’s and Parkinson’s disease.
The detoxifying effect means that L-cysteine can help to keep your liver healthy.
There is also growing acceptance among medical professionals about the benefits of L-cysteine supplements and NAC supplementation. Doctors from the American Academy of Family Physicians report that the benefits of increasing glutathione through L-cysteine supplementation can include: (3)
- reducing the severity of flu infections
- improving lung health and improving the symptoms of chronic lung conditions
- treating stomach infections like the pylori bacteria
- improving fertility
Doctors also report that there are few recorded side effects from L-cysteine supplements. The recommended dose when taking L-cysteine is up to 1,200 mg per day.
Uses and Benefits of L-Cysteine
Let’s look in more detail at the more than 20 ways that L-cysteine supplements can boost your health.
L-cysteine Supplements May Increase Antioxidant Levels
The biggest benefit to your health that L-cysteine supplements provide is their role in boosting antioxidants.
Research into the benefits of taking L-cysteine supplements and NAC supplements has shown that glutathione protects cell function and prevents DNA damage. This has been linked to cancer prevention, boosting cognitive power, and preventing cardiovascular disease. (4)
One 2017 study on rats found that the antioxidant potential of L-cysteine helped to prevent damage to brain tissue. (5)
To help avoid infection, learn about more natural antioxidants in my previous article.
L-cysteine Could Help You Lose Weight
If you are trying to lose weight, then taking L-cysteine capsules daily could aid weight loss because they boost your metabolism and suppress hunger.
Research carried out in London in 2015 found that L-cysteine helps to reduce feelings of hunger in humans. The effect of L-cysteine supplementation helped to suppress a hormone called ghrelin – often called the “hunger hormone.” (6)
Researchers have noted that L-cysteine limits the complications of obesity like inflammation, high blood glucose, and also reduced insulin resistance. (7)
You can get some great ideas in my article on 12 simple tweaks for weight loss.
L-cysteine Can Help Protect Liver Health
L-cysteine supplements benefit your liver because they help prevent damage to liver tissue.
According to scientific studies into L-cysteine and liver support, there are many benefits to taking these amino acid supplements. Researchers found that L-cysteine helps to prevent scarring of liver tissue due to liver damage. (8)
Doctors view L-cysteine in the form of N-acetyl-L-cysteine as an effective treatment for preventing acute liver failure in cases of paracetamol poisoning. (9)
Learn about the 5 dangerous habits that can damage your liver that you must avoid.
L-cysteine Supplementation Can Help Detox
Another way that taking L-cysteine tablets can benefit your general health is that they remove toxins from your system.
Researchers discovered that the effect of cysteine on levels of glutathione helps prevent adverse effects of air pollution. For example, heavy metals like mercury, lead, and arsenic can damage your health over a number of years. L-cysteine supplementation can prevent and treat metal toxicity. (10)
There are other ways to keep your body healthy and detox every day.
L-cysteine Helps Reduce Pain and Inflammation
L-cysteine can help reduce the discomfort that many chronic inflammatory conditions cause.
Clinical research revealed that L-cysteine inhibits certain compounds that cause inflammation. Taking L-cysteine supplements helped to reduce inflammation in the stomach and also boost gut immunity. Researchers recommended L-cysteine as a treatment for inflammatory bowel disorders. (11)
N-acetyl cysteine (NAC) supplements also have an analgesic effect on nerve pain. Research from 2016 found that L-cysteine can reduce the frequency and severity of neuropathic pain. (12)
There are other foods to avoid to help prevent inflammation in the body.
L-cysteine Can Prevent Influenza and Flu Like Infections
By having the ability to boost your immune system, L-cysteine supplements can prevent flu infections.
Researchers found that L-cysteine in the form of NAC can prevent H5N1 influenza A virus infections. Research also revealed that, even if you do get the flu, cysteine helps reduce the severity and length of the respiratory infection. (13)
One study showed that taking N-acetyl cysteine supplements at a dose of 600 mg two times a day significantly improved the symptoms of the flu. The researchers concluded that L-cysteine supplements could reduce the risk of flu complications in the elderly and other high-risk individuals. (14)
Learn how to get rid of the flu faster by using natural treatments.
L-cysteine May Boost Lung Health
As well as reducing the severity of acute upper respiratory infections, L-cysteine supplement capsules can boost your lung health in general.
Research from 2017 found that N-acetyl-L-cysteine can reduce the symptoms of chronic obstructive pulmonary disease (COPD). Regular L-cysteine supplementation destroyed infection-causing bacteria in the lungs. (15)
Taking 1,200 mg a day of NAC can boost the effectiveness of antibiotics when treating chronic bronchitis. (16)
L-cysteine Can Help Manage Type 2 Diabetes
If you suffer from type 2 diabetes then regularly taking an L-cysteine supplement to increase glutathione can help manage your symptoms.
There are 2 ways that L-cysteine benefits diabetics – lowering blood glucose levels and increasing insulin sensitivity.
L-cysteine supplements and blood glucose levels
Some studies show that supplementing your diet with L-cysteine can help control blood glucose levels. Scientists have found that cysteine helps improve glucose metabolism and increase levels of glutathione. (17)
L-cysteine can lower insulin resistance
Research into using L-cysteine to control type 2 diabetes has found that supplements can help increase insulin sensitivity. As well as lowering blood glucose levels, L-cysteine also reduces inflammation in diabetic patients. (18)
There are other foods to control type 2 diabetes.
L-cysteine Promotes Good Mental Health
There is growing evidence to support that fact that L-cysteine supplements can have a positive effect on your cognitive abilities.
Research published in the journal Neuroscience found that L-cysteine has a neuroprotective effect. L-cysteine increases certain compounds that boost the health of nerve cells. (19)
L-cysteine supplements help treat Parkinson’s and Alzheimer’s disease
People with degenerative brain disorders like Parkinson’s disease and Alzheimer’s disease may benefit from L-cysteine supplements.
Research has revealed that people with Parkinson’s disease tend to have low levels of glutathione. Some evidence suggests that L-cysteine supplements could slow down the progress of Parkinson’s disease. (20)
Supplements containing forms of L-cysteine have also shown efficacy in treating Alzheimer’s disease. (21)
L-cysteine May Help With Depression
You can also use L-cysteine or NAC supplements to treat the symptoms of depression.
As far back as 1980, doctors discovered that L-cysteine can help to boost certain chemicals in the brain that are associated with mood. (22)
A review of 5 studies on the effect of L-cysteine in the form of NAC on depression found that it benefits people with depression. There were no adverse effects reported from using this product to treat depression (23)
If you suffer from depression, you can learn about other natural antidepressants.
L-cysteine May Prevent and Treat Psychiatric Conditions
Because L-cysteine improves mental health, it may also help treat psychiatric conditions.
A 2015 systematic review of the effects of N-acetylcysteine on the brain found that it is useful for many mental disorders. For example, NAC supplements of 2,400 mg to 3,000 mg per day can reduce symptoms associated with obsessive compulsive disorder, bipolar disorder, schizophrenia, and autism. (24)
L-cysteine Can Improve Your Obstructive Sleep Apnea Syndrome
A study on adults have shown that long-term L-cysteine supplementation can help treat sleep apnea. (25)
L-cysteine Can Boost Cardiovascular Health
Supplementing your diet with L-cysteine can also benefit your cardiovascular health.
A study from 2014 found that L-cysteine helped to lower blood pressure which is one of the risk factors for heart disease. In fact, when used in conjunction with hypertensive medication, the results were enhanced. (26)
There are other ways to keep your heart healthy.
L-cysteine May Boost Hair Growth
Taking L-cysteine regularly could help boost hair growth and boost the strength of hair.
Scientists say that cysteine is one of the precursors to keratin which is essential for strong hair. In one study, women who were experiencing hair loss due to the menopause were given L-cysteine along with medicinal yeast and vitamin B5. After 6 months, scientists noticed that hair grew back better. (27)
Other studies have shown that L-cysteine can help to improve the signs of alopecia. (28)
Learn about other supplements that can help to combat hair loss.
L-cysteine Promotes Good Digestive Health
L-cysteine supplements can help make your digestion work better.
Medical research has shown that L-cysteine is effective in treating chronic digestive conditions. Scientists say that levels of intestinal glutathione are reduced in people with inflammatory bowel disease. This leads to inflammation and digestive upset. (29)
Studies have shown that L-cysteine supplements help to reduce gut inflammation. These also produce substances in the intestines that are connected to the immune system. The overall effect was that L-cysteine has the potential to reduce digestive upset. (30)
If you feel that your digestion doesn’t work properly, please read this article to naturally treat many digestive conditions.
L-cysteine Can Help Treat H. Pylori Infections
L-cysteine may help treat H. pylori strains of bacteria that cause peptic ulcers and abdominal discomfort.
When examining the protective effect of N-acetylcysteine (NAC), researchers discovered that they help to treat H. pylori infections. NAC supplements also helped to reduce stomach acidity and alleviate gastrointestinal discomfort. (31)
Find out how to use probiotics as a natural remedy for H. pylori infections.
L-cysteine Supplements Can Improve Male Fertility
L-cysteine also has a positive effect on the male reproductive system and can improve fertility in men.
Scientists discovered in 2016 that the ability of N-acetyl-L-cysteine to increase antioxidants has an effect on sperm quality. NAC supplements helped to improve the elasticity and viscosity of semen. The improved semen parameters resulted in increased pregnancy rates. (32)
Learn about ways to increase the length of time that sperm can live to increase fertility.
L-cysteine May Treat Polycystic Ovary Syndrome (PCOS)
Taking L-cysteine supplements could prove useful in treating symptoms of polycystic ovary syndrome. PCOS causes abdominal cramping, irregular periods, and infertility in women.
A review of the benefits of L-cysteine in 2017 reported that it can help alleviate PCOS symptoms. Scientists found that the antioxidant potential of L-cysteine reduces metabolic syndrome, prevents insulin resistance, and help manage blood glucose levels. These are all common complications of polycystic ovary syndrome. (33)
L-cysteine May Have Anticancer Properties
Because L-cysteine increases the number of free radical scavengers in the body, it has a potential use in preventing various cancers. Some research also points to the fact that L-cysteine can also boost the effectiveness of some cancer treatments.
A lab study found that N-acetylcysteine inhibits the growth of certain cancer cells. Cysteine helps prevent cancer cells from multiplying and growing. The scientists concluded that NAC treatment could have a therapeutic effect in treating certain types of tumors. (34)
Another lab study has shown that L-cysteine could assist in inhibiting the growth of gastric cancer tumors. However, more research needs to be done on using N-acetyl cysteine supplementation to treat cancer. (35)
Side Effects of L-cysteine (N-acetyl Cysteine, NAC)
The benefits of L-cysteine supplements and NAC supplements are that they are effective without producing many side effects. In fact, few people report any side effects when taking L-cysteine supplements.
However, you may experience some mild side effects as your body gets used to L-cysteine. The website Drugs.com reports that some reactions to L-cysteine can include the following: (36)
- Mild nausea
- Upset stomach or abdominal discomfort
- Vomiting
- Skin rashes
Precautions When Taking L-cysteine Supplements
L-cysteine supplements are well-tolerated by most people. However, you should speak to your doctor if you are taking certain medications.
For example, because L-cysteine supplements can benefit your blood pressure, you should find out if they will interfere with blood pressure drugs. Also, L-cysteine can thin the blood and may interact with blood-thinning medication.
Food Sources of L-cysteine
L-cysteine is metabolized in your body to become cysteine.
L-cysteine doesn’t naturally occur in food sources. Because cysteine is an amino acid, it naturally occurs animal protein and in some plant protein.
Plant-based cysteine sources
Cysteine occurs in nuts, seeds, whole grains, soybeans, garlic, onions, oats, and legumes.
Animal protein sources of cysteine
Important sources of cysteine and other essential amino acids include turkey, chicken, duck, and pork. There are also levels of cysteine in dairy products and eggs.
L-Cysteine Dosage
There is no recommended daily allowance for taking supplements containing L-cysteine. Some manufacturers recommend taking 500 mg or 600 mg L-cysteine 2 or 3 times a day. You can also use NAC supplements as they also cause the body to produce glutathione.
Doctors on WebMD recommend different doses of L-cysteine (N-acetylcysteine) for specific conditions.
- To reduce the severity of flu infections: Take NAC 600 mg two times a day.
- To treat psychotic disorders: Take L-cysteine 1,200 mg to 2,400 mg a day.
- To treat chronic bronchitis: Take up to 600 mg twice a day.
How to Choose the Best L-cysteine Supplement
It is important to choose good quality L-cysteine supplements to get the best health benefits.
Some of the factors to look for when choosing the best L-cysteine capsules include the following:
- The amount of active or pure L-cysteine
- The number of capsules in each serving
- L-cysteine capsules with as few, if any, fillers as possible
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