The amino acid arginine was first discovered in 1886 in lupin seedlings. It was then found in mammal protein in 1895 and is now known to be semi-essential for human beings. “Essential” amino acids are those that are necessary for life and which cannot be made by the body, hence are essential in the diet. Arginine is not one of these and so is “semi-essential”. However, arginine is considered essential for infants and people under the stress of trauma, infection or burns. While it is not strictly an essential amino acid for adults outside of these categories, the many uses of arginine make it a very desirable supplement.
Food sources
Arginine is found well supplied in protein from meat, fish, chicken, dairy products, nuts and seeds. It can also be found in barley, brown rice, buckwheat, chocolate, corn, oats, raisins and soy. As you can see, arginine is widely available and based on the fact that each gram of dietary protein contains 54mg of L-arginine, the estimates are that adults consuming a normal Western-style diet will be consuming between three and six grams of arginine daily.
Arginine in your body
Arginine is involved in a range of biochemical processes in your body but three of its key actions involve its impact on hormones and nitric oxide production. Like most amino acids, arginine can come as either L-arginine or D-arginine. Since it has a longer half-life and greater long-term effects, L-arginine is the preferred form.
Arginine has been shown to impact on the secretion of the intestinal hormone GLP-1, which in turn affects insulin secretion and therefore affects blood-glucose control. Arginine also triggers the release of growth hormone, which supports immune function by increasing the activity of immune cells including macrophages, natural killer cells, cytotoxic T cells and neutrophils.
The involvement of arginine in the formation of nitric oxide is only a small portion of the function of arginine, but it has received a lot of attention because of the effects of nitric oxide. Although it has a range of metabolic effects, nitric oxide is often noted for its capacity to relax the smooth muscle of blood vessels, making it useful for conditions such as cardiovascular disease and erectile dysfunction. Since arginine promotes nitric oxide manufacture, it too can be useful in these conditions.
Uses
Cardiovascular disease. As well as improving the function of blood vessels via nitric oxide production, arginine is useful in cases of atherosclerosis. There is evidence that arginine supplementation slows the progression of atherosclerosis, although whether it will actually reduce existing plaques is uncertain.
Studies do show that arginine leads to reduced clumping of platelets in the blood, therefore keeping blood flowing at the same time as relaxing blood vessels and promoting blood flow in that way. There is also some evidence that arginine supplementation can reduce overall cholesterol levels. Due to its capacity to relax and dilate blood vessels by promoting nitric oxide production, arginine has also been shown to lower blood pressure and some studies (although not all) show that it can be of help for people suffering angina.
Diabetes. A study in the September 2013 edition of the journal Endocrinology has shown that arginine may be a useful supplement for diabetics. In the study, researchers subjected lean and obese animals to a glucose tolerance test, which measured the body’s ability to remove glucose from blood over time. They found that arginine supplements improved glucose metabolism by as much as 40 per cent in both groups. Arginine was shown to increase the body’s production of glucagon-like peptide-1 (GLP-1), an intestinal hormone that plays an important role in regulating appetite and glucose metabolism by impacting on insulin secretion.
Mice without GLP-1 receptors were not affected to the same extent by arginine. So it does appear that it is via GLP-1 that arginine may have benefits for glucose metabolism.
Erectile dysfunction. The ability to achieve successful erection in men is at least partly dependent on the release of nitric oxide in the penis, causing relaxation of blood vessels and promoting blood flow to the region. In men where nitric oxide production is the issue causing them problems, arginine supplementation at around 5g per day for six weeks has yielded improved sexual function.
Taking L-arginine
Generally, arginine seems to be well tolerated at doses below 30mg daily, but if you are looking at supplementing with this amino acid at any quantity above a few grams daily in addition to food, seek the advice of your healthcare professional.
Broadly, around 9g a day seems to be useful in coronary artery disease, 5g daily for men with erectile dysfunction if abnormal nitric oxide metabolism is their problem, and around 12g a day for people with angina, although the evidence remains uncertain. Human doses to achieve improved blood-sugar metabolism are yet to be established.
Precautions
Generally, arginine is considered safe for humans, but because it does promote nitric oxide production, and this does relax blood vessels, hypotension (low blood pressure) could result from excessive intake of arginine.
Side-effects are rare and mild but some people can experience abdominal pain, bloating, diarrhoea or gout.
If you suffer from cold sores you should minimise your arginine intake. The Herpes simplex virus that causes cold sores has a high requirement for arginine in order to replicate. On the other hand, the amino acid lysine inhibits viral replication. A diet low in arginine and high in lysine may help prevent or treat herpes outbreaks.
- References available on request.
