Dietary L-arginine is found in both plant and animal products; during the past two decades it has also become popular as a
dietary supplement. Arginine is a ‘semi-essential’ amino acid — which means that it is produced in the body in limited amounts, but that an external
source is required during periods of maximal growth, severe stress, and injury. It serves as a precursor for protein, polyamine, creatine and nitric oxide biosynthesis.
What we can’t tell you
In the U.S. and some other industrialized countries, government agencies like the U.S. Food and Drug Administration have adopted
censorship as a method for intensifying their control over the supplement industry and its customers. Thus, FDA regulations
prohibit us from telling you that any of our products are effective as medical treatments, even if they are, in fact, effective.
Accordingly, we will limit our discussion of L-arginine to a brief summary of recent arginine research, and let you draw your
own conclusions about what medical conditions it may be effective in treating.
Arginine plays many roles in the body and has significant effects on:
- tissue growth, including muscle and bone
- wound healing
- energy metabolism
- modulation of vascular tone and cardiovascular function
- immune function
- response to infection
- hormone secretion
- insulin sensitivity
Some, but not all, of these physiologic effects result from arginine’s role as the sole source of the multifunctional messenger
molecule ‘nitric oxide’.
Arginine supplementation improves outcomes in animals with infections, wounds, burns, and other injuries, with no significant
detrimental effects. It functions as a secretagogue, stimulating the release of growth hormone, insulin-like growth factor type 1, insulin, and
prolactin. Arginine also stimulates T-cell and natural killer cell activity and influences pro-inflammatory cytokine levels.
Arginine enhances collagen deposition and tissue strength in artificial incisional wounds in rodents and humans. Arginine
supplementation has been proposed to normalize or enhance wound healing in humans.
In a randomized double-blind study of the effect of oral arginine supplementation on wound healing and T-cell function in
people more than 65 years of age, forty-five elderly, healthy volunteers received experimental wounds in one shoulder and
in the upper thigh. Daily supplements of 17 gm free arginine (in the form of arginine aspartate) were given to thirty subjects
for two weeks. The fifteen other wounded subjects received a placebo syrup. The results suggested that arginine supplementation
improves wound healing and immune responses.
Growth factors and muscle function
L-arginine supplements have been popular for years as promoters of growth hormone production in the human body. Clinical trials
to test this idea produced little more than confusion until it was realized that very large doses (around 40 grams per day)
are required when arginine is used by itself.
Dual amino-acid supplementation with L-arginine and L-lysine, on the other hand, increases growth hormone levels without the
need for large doses of either supplement. Studies using 1200-1500 mg of each supplement showed that significant increases
in growth hormone levels take place in the blood from 30 to 90 minutes after consumption. It appears that the best time to take arginine+lysine is when one is resting — not when one is about to exercise. Exercise
itself causes growth hormone levels to rise, and this effect nullifies the advantage gained from the supplements.
Muscle function in the elderly typically declines, regardless of the amount of exercise performed. Among the important causes
of this decline are deficiencies in the growth factor ‘IGF-1’ (insulin-like growth factor) and the amino acid ‘cysteine’.
Supplemention with arginine and N-acetylcysteine (NAC) can correct these deficiencies. A clinical trial in 2003 showed that
the muscular response to physical exercise in frail geriatric patients was ‘strongly enhanced’ by arginine+NAC supplementation.
IGF-1 is a key promoter of muscle growth in people of all ages — in fact, the growth effects of growth hormone and of anabolic
steroids like testosterone may result from the induction of IGF-1 production in the body rather than any direct effects on
the muscles by these hormones themselves. It is therefore of interest that the production of IGF-1 is promoted directly by
arginine at doses somewhat smaller than that required to raise growth hormone concentrations. One study showed that 17 grams/day
of arginine caused significant elevation of IGF-1 levels.
Bone injuries and osteoporosis
In experiments with guinea-pigs, it was shown in 2004 that high-dose arginine supplements taken orally for 4 weeks accelerated
the healing of bone fractures and resulted in stronger bones.
Experiments have demonstrated that the amino acids arginine and lysine, used in combination, stimulate the growth of bone
cells and improve the structure of collagen in osteoporotic bone tissue. Researchers concluded that “administration of these
amino acids may be useful in clinical treatment and prevention of osteoporosis.” Arginine by itself does not work — a clinical trial using 14.8 g/day of L-arginine in postmenopausal women showed no prevention
of bone loss. When the medical world eventually gets around to studying the arginine+lysine combination as an osteoporosis therapy, smaller
dosages will undoubtedly be used — like those mentioned above in ‘Growth factors and muscle function’.
Arginine is the body’s sole source of nitric oxide, a substance which serves as a messenger in the blood and regulates vascular
tone and blood dynamics. It is therefore not surpising that arginine has effects on processes that damage the cardiovascular
system. Compelling evidence shows that the administration of arginine reverses the damage to blood vessels and heart that
is associated with major cardiovascular risk factors (high cholesterol, smoking, hypertension, diabetes, obesity, insulin
resistance, and aging) and ameliorates many cardiovascular disorders, such as coronary and peripheral arterial disease, injuries
caused by blood clots, and heart failure.
Immunity, surgical complications
Thirty cancer patients undergoing major operations were studied in a clinical trial of 25 g/day of arginine as an immune booster
to prevent post-surgical complications. Supplemental arginine significantly enhanced immune responses, and the investigators
concluded: “As a nutrient substrate, arginine was nontoxic, and may benefit surgical patients who are at increased risk of
Are L-arginine supplements useful for the conditions and purposes mentioned above? We aren’t allowed to tell you, so you should
take a look at some of the references cited here, and then decide for yourself.