Arginine is a semi essential amino acid that can be synthesized in the body from other amino acids (eg citrulline, glutamine, glutamate, proline, ornithine). During times of physical stress however, such as following an injury or surgery, arginine is often in short supply and becomes essential in the diet.
Arginine is obtained from protein-rich foods such as nuts, seeds, egg yolk, red meat and pulses. It is also found in beetroot, onions, grapes and rice.
l-arginine versus d-arginine
Arginine is usually written as l-arginine on supplement labels, where the L stands for levo. This shows the supplement contains the natural isomer of arginine which rotates light to the left. Synthetic arginine will also contain the mirror image isomer, d-arginine, which rotates light to the right (dextrorotatory). D-arginine is largely inactive in the body but can be toxic in high doses as it is not broken down in the same way as l-arginine. Wherever I mention arginine here, I am referring to l-arginine.
What does l-arginine do?
The breakdown of l-arginine releases a number of active substances, including nitric oxide (a powerful blood vessel dilator), glutamate and agmatine (neurotransmitters) plus creatine (an energy storage molecule).
L-arginine is an important source of nitric oxide (NO) which is a powerful blood vessel dilator. NO is vital for regulating blood pressure in men and women, and normal erectile function in males.
As an amino acid, arginine is also involved in the production of insulin, glucagon growth hormone and antidiuretic hormone (vasopressin). It plays a role in collagen synthesis and wound healing and is therefore needed in greater amounts during recovery from surgery, injuries and burns.
Arginine is also used to make creatine phosphate, an energy-storing and energy-creating molecule which is a popular supplement to boost muscle strength and endurance.
Lack of arginine is linked with poor wound healing, hair loss, skin rashes, constipation and fatty liver changes.
Arginine for men
Arginine benefits men by dilating arteries and boosting blood flow to the penis through effects on nitric oxide, in a similar way to prescribed erectile dysfunction drugs. L-arginine can improve erectile function and is often combined with other pro-sexual supplements for maximum effect.
The combination of L-carnitine, L-arginine and niacin (vitamin B3) was tested in 51 patients attending an Italian erectile dysfunction clinic. After 3 months of treatment, a statistically significant improvement was found, with improved erections in 40% of cases, and at least a partial response in up to 77%.
The combination of l-carnitine, l-arginine and vitamin B3 also improved the response to prescribed medication for erectile dysfunction (vardenafil) in 40 men with erectile difficulties relating to diabetes.
A Japanese trial involving men with mild to moderate erectile dysfunction found the combination of Pycnogenol 60 mg together with L-arginine 690mg and aspartic acid 552 mg daily was significantly more effective than placebo. After 8 weeks, there was a marked improvement in ‘hardness of erection’ and ‘satisfaction with sexual intercourse’. A decrease in blood pressure and a slight increase in salivary testosterone were also found in those taking the active supplements.
Arginine and sperm health
As much as a quarter of the protein in seminal fluids is in the form of l-arginine which supplies nitric oxide and creatine to fuel sperm motility. In men with a low sperm count, and inactive sperm, l-arginine helped to improve sperm motility compared with placebo when used in combination with l-carnitine and ginseng or with l-citrulline and pine bark extracts (Prelox).
Arginine for women
L-arginine increases production of nitric oxide which plays an important role during sexual arousal in both men and women. L-arginine supplements have been shown to improve all aspects of female sexuality including interest, arousal and satisfaction. It can take up to six weeks for L-arginine to produce an optimum effect.
Arginine and blood pressure
By promoting blood vessel dilation, L-arginine can lower blood pressure. Results from 11 clinical trials involving 387 people with hypertension, found that doses of oral l-arginine ranging from 4g to 24g per day lowered blood pressure significantly more than placebo, by an average of 5.39/2.66 mmHg.
In those with borderline hypertension, reductions of 11/4.9mmHg have been recorded (at a total daily dose of 2.1g l-arginine sustained release) within one week, together with a 23% improvement in arterial elasticity. In those with normal blood pressure, there were no significant changes so it is unlikely to cause blood pressure to go too low.
Arginine and pre-eclampsia
High blood pressure during pregnancy (pre-eclampsia) has been treated with l-arginine to promote blood vessel dilation and improve blood flow through the placenta. The results from seven clinical trials involving 884 women at risk of pre-eclampsia, found that l-arginine reduced the development of pre-eclampsia by 56% compared with placebo, and reduced the risk of preterm birth by 52%. In women with established hypertension, L-arginine supplements reduced the severity of pre-eclampsia by 79%. It’s important to only take supplements during pregnancy under medical supervision, however.
Arginine and heart failure
L-arginine may improve congestive heart failure by promotion blood vessel dilation, increasing arterial blood flow, prolonging exercise duration and increasing the distance that can be walked.
Arginine and immunity
L-arginine plays an important role in wound healing and regulation of immune responses and inflammation. Data from 11 trials involving 321 people with reduced immunity (hospitalised due to cancer, pressure sores, burns, HIV or advanced age) found that taking l-arginine supplements significantly improve the immune responses of CD4⁺ T-cells and reduced the incidence of infections (pneumonia, abscess, sepsis, urinary or wound infections) compared with controls. https://www.ncbi.nlm.nih.gov/pubmed/25164444
A typical dose is 2g to 3g l-arginine up to three times daily. When taken for its beneficial sexual actions, it should ideally be taken one hour before sex.
It can take between two and six weeks for L-arginine to achieve its optimum effect.
l-arginine is often combined with l-citrulline from which l-arginine can be made in the body.
An Observed Safe Level risk assessment based on published clinical trial data found an absence of adverse effects for l-arginine at intakes of up to 20g per day in normal healthy adults. Doses above 20 g daily are therefore not recommended except under medical supervision (eg to treat resistant hypertension or heart failure).
Side effects are uncommon, but high doses or l-arginine may cause diarrhoea.
Reversible thickening and coarsening of the skin has been reported with long term use.
Some evidence has suggested that L-arginine helps replication of herpes viruses and may stimulate a recurrence of Herpes simplex infections (cold sores) although this is not proven.
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