Cysteine is a semi-essential amino acid.

It’s considered semi-essential because your body can produce it from other amino acids, namely methionine and serine. It becomes essential only when dietary intake of methionine and serine is low.

Cysteine is found in most high protein foods, such as chicken, turkey, yoghurt, cheese, eggs, sunflower seeds, and legumes.

N-acetyl cysteine (NAC) is a supplement form of cysteine.

Consuming adequate cysteine and NAC is important for a variety of health reasons, including for replenishing the most powerful antioxidant in your body, glutathione. These amino acids also help with chronic respiratory conditions, fertility, and brain health.

Here are the top 9 health benefits of NAC.

1. Essential for making the powerful antioxidant glutathione : NAC is valued primarily for its role in antioxidant production. Along with two other amino acids — glutamine and glycine — NAC is necessary to make and replenish glutathione. Glutathione is one of your body’s most important antioxidants — compounds that help neutralise free radicals that can damage cells and tissues in your body. It’s essential for immune health and for fighting cellular damage. Some researchers believe it may even contribute to longevity.

2. Helps with detoxification to prevent or diminish kidney and liver damage: NAC plays an important role in your body’s detoxification process. It can help prevent side effects of drugs and environmental toxins. In fact, doctors regularly give intravenous NAC to people with an acetaminophen overdose to prevent or reduce kidney and liver damage.

3. May improve mental health conditions and substance use disorder: NAC helps regulate levels of glutamate, the most important neurotransmitter in your brain. While glutamate is required for normal brain activity, excess glutamate paired with glutathione depletion can cause brain damage.This may contribute to mental health conditions such as bipolar disorder, schizophrenia, obsessive-compulsive disorder (OCD), and substance use disorder 

4. Helps relieve symptoms of respiratory conditions: NAC can relieve symptoms of respiratory conditions by acting as an antioxidant and expectorant, loosening mucus in your air passageways. As an antioxidant, NAC helps replenish glutathione levels in your lungs and reduces inflammation in your bronchial tubes and lung tissue. A review of multiple studies found that 600 mg of NAC twice a day significantly improved lung function and symptoms in those with stable COPD and that higher doses were more effective than lower ones.  People with chronic bronchitis can also benefit from NAC.In addition to relieving COPD and bronchitis, NAC may improve other lung and respiratory tract conditions — such as cystic fibrosis, asthma, and pulmonary fibrosis — as well as symptoms of nasal and sinus congestion due to allergies or infections 

5. Boosts brain health by regulating glutamate and replenishing glutathione: NAC’s ability to replenish glutathione and regulate brain glutamate levels can boost brain health. The neurotransmitter glutamate is involved in a broad range of learning, behaviour, and memory functions, while the antioxidant glutathione helps reduce brain cell oxidative damage that is associated with ageing 

6. May improve fertility in both men and women: Many male infertility issues increase when antioxidant levels are insufficient to address free radical formation in the reproductive system. The oxidative stress can cause cell death and reduced fertility. In some cases, NAC has been shown to improve male fertility. One condition that contributes to male infertility is varicocele — when veins inside the scrotum become enlarged as a result of free radical damage. Surgery is the primary treatment. In one study, 35 men with varicocele received NAC daily for 3 months after surgery. The combination of surgery and NAC supplementation improved semen integrity and partner pregnancy rate by 22% compared with the control group.  In addition, NAC may improve fertility in women with polycystic ovary syndrome (PCOS) by inducing or augmenting the ovulation cycle, although more research is needed.

7. May stabilise blood sugar by decreasing inflammation in fat cells: High blood sugar and obesity contribute to inflammation in fat tissue. This can lead to damage or destruction of insulin receptors and increase the risk of type 2 diabetes.

8. May reduce heart disease risk by preventing oxidative damage: NAC may reduce heart disease risk by reducing oxidative damage to tissues to the heart.  It has also been shown to increase nitric oxide production, which helps veins dilate and improves blood flow. This expedites blood transit back to your heart and can lower your risk of heart attacks

9. Ability to boost glutathione levels may improve immune function: NAC and glutathione also benefit immune health. Research on certain diseases associated with NAC and glutathione deficiency suggests that supplementing with NAC might improve — and potentially restore — immune function,  This factor has been studied most in people with HIV. In two studies, supplementing with NAC resulted in a significant increase in immune function, with an almost complete restoration of natural killer cells 

References

Mokhtari, V., Afsharian, P., Shahhoseini, M., Kalantar, S. M., & Moini, A. (2017). A Review on Various Uses of N-Acetyl Cysteine. Cell journal, 19(1), 11–17. https://doi.org/10.22074/cellj.2016.4872