You might not have heard of N-acetylcysteine, or NAC, but it may well be one of the most important supplements on your health-shop's shelves. It's well known in the medical world as a mucus-thinner as well as an antidote for paracetamol overdose, but recent research has also revealed a multitude of other possible uses for the sulphur-containing substance-from treating autism to preventing cancer.
The latest research suggests that NAC may have a role to play in treating autism. In a preliminary study, researchers from Stanford University in California looked at 33 autistic children aged from three to 11 years for 12 weeks, after giving half of them a placebo and the other half NAC. The dosages used were 900 mg daily for four weeks, followed by 900 mg twice a day for the next four weeks and then 900 mg three times daily for the final four weeks.
By the end of the trial, the children in the NAC group were experiencing significant improvements in symptoms of irritability, such as throwing, hitting and kicking, compared with the placebo group, while their average scores according to the 'Aberrant Behaviour Checklist' dropped by nearly half. The NAC-treated children also showed a decline in standardized measures of repetitive and stereotypical behaviours, such as rocking and finger-flapping (Biol Psychiatry, 2012; 71: 956-61).
Given that dangerous antipsychotic drugs are the standard treatment for irritability in autism, this is promising news for the 60-70 per cent of sufferers who are affected by it. Research is now underway to determine whether NAC is effective for other symptoms of autism and in larger groups of children.
Polycycstic ovarian syndrome, or PCOS, may also be improved by NAC. One study showed that many of the common symptoms, including excess body hair (hirsutism), insulin resistance and menstrual irregularity, can be treated just as effectively with NAC as with the drug metformin, which is commonly used to manage such symptoms. A dose of 600 mg of NAC three times daily was equally as effective as 500 mg of metformin three times daily, according to Turkish researchers (Eur J Obstet Gynecol Reprod Biol, 2011; 159: 127-31).
Another trial-carried out at the Infertility and Reproductive Health Research Center at Iran's Taleghani Hospital in Tehran-examined the effect of adding NAC to the standard clomiphene citrate (CC) drug treatment for infertility associated with PCOS. CC is used to stimulate ovulation and increase the chances of pregnancy.
The study involved 180 infertile PCOS patients who were split into two groups: one group received 100 mg of CC along with 1200 mg of NAC; the other received CC and a placebo. The results showed that both ovulation and pregnancy rates were significantly higher in the CC plus NAC group compared with the CC plus placebo group, and that NAC had no adverse effects (J Obstet Gynaecol Res, 2012 Apr 30; doi: 10.1111/j.1447-0756.2012.01844.x).
There is also evidence suggesting that NAC may be a useful supplement to take during the flu season for at-risk groups such as the elderly. An Italian study compared the effects of long-term NAC supplementation with a placebo in a group of 262 frail older adults. They were randomly given either 600 mg of NAC twice daily or a dummy pill during the period leading up to and including the flu season, for a total of six months.
The researchers reported that the NAC group were much less likely to come down with flu than the placebo group (25 per cent of those taking NAC developed flu symptoms compared with
79 per cent of those taking the dummy pill). What's more, flu episodes in the NAC group were, on average, much less severe (Eur Respir J, 1997; 10: 1535-41).
NAC may even have a part to play in preventing post-surgical complications. According to several studies, it's effective for preventing a common form of irregular heart beat (atrial fibrillation) that can occur after heart surgery. One meta-analysis that pooled the results of eight randomized controlled trials found that NAC reduced the incidence of postoperative atrial fibrillation by about 40 per cent (BMC Cardiovasc Disord, 2012; 12: 10).
Other evidence suggests that NAC might help to prevent lung-related complications in patients undergoing oesophagectomy (removal of part or all of the oesophagus) as part of their cancer treatment (Dis Esophagus, 2007; 20: 399-405).
Laboratory research has revealed that NAC has potential for both the prevention and treatment of certain types of cancer, including tumours of the lung, skin, head and neck, breast and liver. It appears to be directly anticarcinogenic in itself, but it also works by inhibiting the cancer-causing effects of certain compounds. Interestingly, animal and test-tube studies have also suggested that NAC can selectively protect normal cells-but not malignant ones-against chemotherapy and radiation toxicity (Altern Med Rev, 2000; 5: 467-71).
People with degenerative brain disorders such as Alzheimer's disease may also benefit from taking NAC.
A placebo-controlled trial conducted at the Albuquerque Veterans Affairs Medical Center in New Mexico studied the effects of six months of NAC supplementation in patients with probable Alzheimer's. On testing after three and six months of treatment, the NAC group showed improvements over the placebo group in nearly every outcome tested. However, the results were only significant for a small subset of cognitive (mental) tasks (Neurology, 2001; 57: 1515-7).
Other research-albeit in a mouse model of disease-has indicated that NAC could be useful for Parkinson's disease, too (Brain Res, 2000; 859: 173-5).
Even though NAC has been around for years, it appears that scientists are only just beginning to tap into its huge potential. Because of its mechanism of action (see box above), a whole host of diseases and conditions could, in theory, be helped by this seemingly super supplement.
Factfile: What is NAC?
NAC is a sulphur-containing compound derived from the amino-acid cysteine, which is found in most high-protein foods. It plays a crucial role in our body's natural defence system, as it increases levels of glutathione-the body's main antioxidant. Glutathione is critically important for detoxifying an array of toxic substances, such as xenobiotics (chemicals not normally found in the body) and various free-radical-generating molecules that can cause damage to the cells of the body. It is this detoxifying and cell-protecting effect that is thought to be behind NAC's benefits in numerous diseases and conditions.
NAC has been used and studied for decades, and appears to be safe at dosages up to 1200 mg twice daily. At these dosages, side-effects are unusual, but may include nausea, vomiting, diarrhoea, flushing and constipation. With much larger doses-such as those used to treat paracetamol overdose in hospitals-side-effects such as headache, ringing in the ears, chills, fever, hives and dangerous allergic reactions have been reported (Am Fam Physician, 2009; 80: 265-9).
In healthy people, NAC is generally not recommended in high doses as it may act as a pro-oxidant rather than an antioxidant, lowering levels of glutathione. Indeed, a dose of 1200 mg/day for four weeks, followed by 2400 mg/day for a further two weeks, had this effect in one small trial (Eur J Clin Pharmacol, 1992; 43: 639-42).