Cysteine is referred to as a semi-essential amino acids. We refer to it as semi-essential because the body is capable of producing cysteine from other amino acids methionine and serine. When dietary intake of methionine and serine are low, cysteine becomes an essential amino acid.
Cysteine can be sourced from many high-protein foods like chicken, eggs, sunflower seeds, and legumes. However, food sensitivities or medical conditions that prevent them from getting their sufficient amount of cysteine. When that happens, that’s the right time to consider supplementation. N-Acetyl Cysteine, N-Acetyl L-Cysteine or simply NAC is a supplement form of cysteine. NAC supplements are recommended over L-cysteine as it is better absorbed by the body.
NAC is gaining popularity for the fact that it’s vital for many purposes, among them are replenishing antioxidant stores and fertility.
NAC is primarily known for one thing and that is to jump start the processes involved in producing glutathione, the body’s most abundant and most powerful antioxidant. Together with amino acids glutamine and glycine, NAC is a primary component of glutathione. 
Glutathione is the body’s first line of defence against free radicals that damage tissues and cells in your body. It is also vital for having optimum immunity against bacteria, helping to lower the risks of infections.
When the liver is exposed to excessive toxin levels, glutathione is used to help remove said toxins. However, this also causes glutathione levels to drop. Having adequate levels of glutathione is critical to liver function, and as we mentioned earlier, NAC supports glutathione production. 
Our kidneys also benefit from NAC by mitigating inflammation which can lead to kidney failure, especially for patients with weak kidney organs. 
NAC is involved in the regulation of glutamate levels, one of the most important neurotransmitters in the brain. Studies show excess glutamate, together with glutathione depletion, can result to brain damage. If not treated, this can lead to mental health conditions such as obsessive-compulsive disorder (OCD), schizophrenia, and addictive behaviour. 
Studies show NAC supplementation can help with those conditions.
Some reports suggest infertility issues increase when antioxidant levels are too low to fight free radical damage in the reproductive system. This can lead to cell death and reduced fertility.
Some scientists agree NAC can help with fertility problems, citing positive effects on semen quality after 26 weeks of supplementation in men with infertility problems. 
For women with polycystic ovary syndrome, a condition that makes it difficult for women to have children on top of other symptoms, NAC has been shown to improve ovulation, pregnancy rates, as well as live births compared to placebo. 
Oxidation happens to heart tissue and can lead to increased risks of strokes, heart disease, and heart attacks. Taking NAC supplements could help lower these risks by means of protecting heart tissues from oxidative damage. It can also boost nitric oxide production which can help improve blood flow and manage blood pressure. 
As we mentioned earlier, glutathione can help strengthen the immune system, and NAC supplements can augment glutathione stores. It also appears that people with an impaired immune system benefit the most from NAC supplements, with some studies showing a significant increase in immune function. 
Other studies suggest an anti-carcinogenic effect to NAC supplementation, demonstrating its ability to not only induce cancer cell death, but also block cancer cell replication. 
Insulin helps remove sugar from the bloodstream. Chronic elevated sugar levels can contribute to insulin resistance, a state where insulin has difficulty scavenging sugar, and can result to Type 2 Diabetes. Some researchers suggest taking NAC supplements can balance blood sugar levels by decreasing inflammation in fat cells that leads to higher insulin sensitivity. 
Cysteine is a semi-essential amino acid that can be found in high protein sources such as eggs, legumes, and meat. It is involved in various processes inside the body including detoxification, immune system response, and blood sugar management. N-Acetyl Cysteine or NAC is the supplement form of Cysteine which is available in powder and capsule form.