L-Cystine: What is L-Cystine and Why You May Need It in Your Diet

L-Cystine: What is L-Cystine and Why You May Need It in Your Diet


In the world of dietary supplements, the superstars have been vitamins and minerals. They are the ones that get a lot of publicity and attention. In fact, globally, vitamin and mineral supplements make up well over 50% of dietary supplements consumed. In Singapore, of the S$490 million spent on health supplements in 2017, vitamins took the lead.


Of course, there is more that our body needs. One class of dietary supplements that we can benefit from is amino acids. We tell you more about one type of amino acid – L-Cystine – and why you need to know about it and include it in your diet.

What is L-Cystine

L-Cystine is a semi-essential amino acid, so named because our bodies can make it from the amino acids serine and methionine but only in small amounts and not without enough folate, and Vitamins B6 and B12. Whatever other amounts of L-Cystine that we may need has to be derived from either our diets or from health supplements.


Along with two other amino acids – glutamine and glycine – L-Cystine is needed to manufacture glutathione which is a master antioxidant. We need antioxidants in general because they are substances that inhibit oxidation which is a chemical reaction that produces free radicals. Free radicals are unstable molecules that cause harm to our bodies by damaging our cells. As a result, they are linked to a variety of illnesses including diabetes, heart disease and cancer as well as to ageing.


Amongst antioxidants, glutathione is considered the most powerful. It is so vital to our health that researchers who study longevity believe that the level of this antioxidant in our cells may be a predictor for how long we will live. This, in no small way, lends to the importance of L-Cystine to our health.

Health Benefits of L-Cystine

Fights oxidative stress


As a precursor of glutathione, a super antioxidant, and as an antioxidant itself, L-Cystine can help fight oxidative stress.


Oxidative stress happens when there is an excess of free radicals in our cells. Free radicals are oxygen-containing molecules produced during normal chemical processes such as metabolism when oxygen in the body splits into single atoms with unpaired electrons. Because electrons do not like to exist in uneven numbers, these free radicals will seek out other electrons to pair with, damaging cells, proteins and DNA in the body in the process, and causing ageing and illnesses. Antioxidants mitigate this damage by giving an electron to a free radical so they do not scavenge from other electrons. In essence, antioxidants clean up free radicals.


As a result of its antioxidant properties, L-Cystine also supports immune function. Research suggests that L-Cystine supplements can improve immunological functions in diseases associated with a Cystine and glutathione deficiency. There are studies that show that L-Cystine has the ability to boost the immunity of HIV patients. There are also studies that suggest that L-Cystine can improve immune function in postmenopausal women.


L-Cystine may help prevent exercise-induced overproduction of free radicals as well although the sample size of the study is small. In a 2007 study, 10 male basketball players were given L-Cystine supplements for a week. The supplement helped boost antioxidant capacity and reduce free radical production in the participants.

Regulates glutamate levels


L-Cystine helps to regulate glutamate levels. Glutamate is the most abundant neurotransmitter in our brains and central nervous systems. It is involved in almost every major excitatory brain function (brain functions where the neuron fires an action potential or nerve impulse allowing messages to be spread through the neural circuit). As such, brain neurotransmitter glutamate is important to the signalling speed and information processing functions of the brain, impacting both learning behaviours as well as memory capacity.


Glutamate is also a metabolic precursor of gamma-aminobutyric acid (GABA), another neurotransmitter. GABA is the main inhibitory neurotransmitter in the central nervous system, necessary for decreasing the likelihood that neurons will fire an action.


There is some evidence that because L-Cystine affects glutamate levels, it can improve brain health. However, more research on humans need to be done for this to be conclusive.

Promotes detoxification


Toxic metals have pro-oxidative effects and they deplete glutathione levels. L-Cystine supplements help restore those levels. So, L-Cystine can help the liver detoxify a wide range of toxic metals, pollutants and drug reactions. It has long been used for treating paracetamol overdoses, reducing damage to the liver and kidney which can be fatal.

Relieves symptoms of some respiratory conditions


L-Cystine can break up mucus so that it is easier to cough up phlegm caused by respiratory and pulmonary conditions. Because of its mucolytic properties (ability to break down mucus), L-Cystine can reduce the severity and frequency of wheezing and respiratory attacks especially those caused by chronic bronchitis or allergies.


L-Cystine has been found to be effective against certain strains of influenza pneumonia as well because of its anti-viral properties. In addition, L-Cystine is thought to be useful in treating H1N1 although more research is needed.


L-Cystine has anti-inflammatory properties, helping it to reduce inflammation in the lungs of patients with chronic obstructive pulmonary disease (COPD) and improve airflow to the lungs.

Protects against hearing loss 

L-Cystine may have protective effects against noise-induced hearing loss. High levels of noise can induce oxidative stress in the cochlea by decreasing blood flow and stressing the mitochondria. Since L-Cystine can combat oxidative stress, it can neutralise these effects, protecting against hearing loss.


Studies on animals and human appear to bear out this fact. In a study, nearly 400 people were given oral doses of L-Cystine before being exposed to loud noises. It was found that the protective effects of the supplement against noise-induced hearing loss were more prominent in the group given the supplement compared to the control group which was given placebos. A Taiwanese study of male workers in noisy environments provided doses of L-Cystine suggested similar protective effects against noise-induced hearing loss.

Improves hair quality

L-Cystine is important for hair health. As one of a few amino acids that can form disulphide bonds in the body, it helps to hold keratin strands within the hair together, helping hair with its fibrous properties that enable it to retain moisture. L-Cystine also helps to maintain the texture and thickness of hair. That is why many topical hair products have L-Cystine as a major ingredient.


A German study found that L-Cystine can decrease hair loss while improving hair growth. People who suffered massive hair loss were divided into two groups. One was treated with a combination of L-Cystine, millet seed extract, and pantothenic acid while the other group was given a placebo. After three months, those treated with the L-Cystine combination showed a decrease in hair loss and their natural hair growth was restored.

Protects skin


L-Cystine helps skin that has been damaged by the sun by aiding in the formation of enzymes in skin cells. These enzymes keep the p53 gene active. p53 is a tumour suppressing gene that can detect changes in the skin’s DNA that might cause cancer and can shut down these cells. L-Cystine is also important for the formation of the caspases that dissolve the cell when it dies.



Health benefits that require more research

Some have suggested that L-Cystine can improve male fertility, balance blood sugar levels, support digestive health and treat psychiatric disorders but more evidence is required before these claims can be conclusive.


Sources of L-Cystine


Apart from being produced in small quantities by the body, we can get L-Cystine from high protein foods as well as supplements. One major source of dietary L-Cystine is animal proteins including meats such as chicken, turkey, duck, pork, veal, lamb, beef bison, and fish like bluefish, yellowtail, salmon and tuna as well as eggs and dairy products, for example, yoghurt and cheeses (ricotta and cottage cheese). Plant-based L-Cystine can be found in nuts, seeds like sunflower seeds and pumpkin seeds, oat bran and legumes like beans, soybeans and lentils. Vegetables that have L-Cystine are onions, garlic and broccoli.

Buying L-Cystine Supplements


L-Cystine as a dietary supplement comes in capsule, tablet and powder form. It can often be found in protein powders including whey and plant-based proteins.

California Gold Nutrition, L-Cystine, AjiPure, 500 mg, 60 Veggie Capsules

Sourced exclusively from Ajinomoto, a Japanese food and biotechnology corporation, this health supplement is produced via their patented Ferment-A-Pure Technology and is pharmaceutical grade. A vegan-friendly option which contains no animal products, it is also free of gluten, GMO and soy.

DHC Japan L Cystine White 240 Whitening Supplements 180 Tablets

Apart from promising to lighten the skin, this supplement is also said to suppress the production of melanin which can be caused by lack of sleep, stress and UV rays. Melanin is responsible for hyperpigmentation that causes spots, freckles and uneven skin tone as well as for darkening complexion.


L-Cystine also enhances the production of proteins, glutathione, taurine, coenzyme A and other inorganic sulfates in the body. Apart from L-Cystine, the tablets contain 50mg of Vitamin E to improve blood circulation and promote the skin's healthy metabolism.

Hythiol-C Plus Vitamin C SS Seiyaku supplement 180 tablets L Cystine 240mg

This supplement helps to rid the skin of melanin deposits and prevent the production of more melanin that causes skin blemishes. It also aids the metabolic functions of the liver and converts nutrients into energy, curing fatigue and listlessness.

Chocola BB Lucent C 180 tablets Vitamin C L-Cystine Eisai acne age-spots

Launched by Japanese company Eisai, the Chocola BB line of health supplements and beauty products was created to enhance women’s beauty and health. These tablets aim to lighten blemishes and brown spots on the skin, two of the most common skin problems among women.


Oxidation in pigment cells of the skin can cause excessive melanin products resulting in poor complexion and dark skin. The tablets which contain both Vitamin C and L-Cystine are designed to combat these effects. The added Vitamins E, B2 and B6 in the formula help to improve blood flow to the epidermis and improve skin metabolism to restore skin health.

Now Foods, L-Cystine, 500 mg, 100 Tablets

From the US-owned and operated Now Foods comes this L-Cystine supplement which also contains Vitamins B6 and C which help to aid the body’s production of L-Cystine. The non-GMO tablet is also soy free, nut free, gluten free, dairy free, egg free, Halal and Kosher. NPA A-rated GMP certification, every aspect of the Now manufacturing process is examined, including their laboratory and testing methods, for stability, potency and product formulation.

Dosage of L-Cystine

N-Acetyl Cystine (NAC) is the form of L-cystine that is found in nutritional supplements. Doses of around 500 to 600mg are generally safe. The safety of supplements for pregnant women, nursing mothers, children and those with medical conditions or who are taking medications have not been established though some studies indicate it can be safe for pregnant women.


However, very high doses of L-Cystine – seven grams or more – can be toxic to human cells. L-Cystine supplements should not be taken with other medications that suppress the immune system, oxiconazole (an antifungal medication), nitroglycerin and isosorbide (medication for high blood pressure), or activated charcoal. Because of the potential for side effects and interactions with medications, the supplements should only be taken under the supervision of a doctor.


Some may experience side effects from L-Cystine supplements including dry mouth, headache, dizziness, nausea, vomiting and diarrhoea. Adverse dermatological effects such as elevated blood pressure, fatigue, muscle pains, insomnia, nasal congestion, runny nose, restlessness, vivid dreams, and irritability have also been reported.