L-arginine has previously been found to lower blood pressure and is often included in nutritional supplements recommended for heart patients.
But a small trial on middle-aged men shows that the amino acid may also benefit the heart through its effect on homocysteine, increasingly considered a marker for heart disease risk.
Observational studies have found that, on average, people with high levels of homocysteine in their blood are more likely to have a stroke. This means that L-arginine could have wider implications for heart health than currently believed.
Stroke is the third most common cause of death in developed countries. There are 125,000 cases of stroke in the UK each year and 60,000 deaths.
In a randomized, placebo-controlled, crossover study, researchers from Pennsylvania State University, Kraft Foods and INRA in France tested the effects of a daily 12g dose of L-arginine on 16 middle-age men with hypercholesterolemia.
After each treatment, the team measured blood circulation variables at rest and during two tasks designed to put the heart under stress.
L-arginine had a modest effect on blood pressure - enough to reduce heart disease risk but not enough to allow someone to stop taking blood pressure lowering medication.
However the researchers also found that its presence in the blood was inversely related to a change in plasma homocysteine.
"This study is the first to describe a haemodynamic mechanism for the hypotensive effect of oral L-arginine and the first to show substantial reductions in homocysteine with oral administration," say the authors in this month's issue of the Journal of Nutrition (135, pp212-217).
"We were not expecting the significant reductions in homocysteine, another cardiac risk factor that has received a lot of attention lately. That may be more important than modest BP reductions," lead author Dr Sheila West, assistant professor of Biobehavioral Health at Pennsylvania University, told NutraIngredients.com.
She added that some arginine-rich foods, such as beef, are high in saturated fat and methionine, an amino acid that increases homocysteine.
"If our findings on homocysteine lowering hold up, that could be an important new application for arginine."
The researchers are seeking funding to continue their work on the amino acid and are looking for opportunities to work with industry groups who want to conduct clinical trials of their arginine products.
"We are currently studying foods that are high in arginine such as pistachios and walnuts. These nuts combine L-arginine, fibre, antioxidant vitamins, and unsaturated fatty acids. All of these nutrients may work together to improve vascular health," said Dr West.
She noted that other research suggests that the blood pressure-lowering effects of arginine are larger in subjects with higher blood pressure.
In the current trial, subjects had blood pressure in the normal range, although not as low as it could be for optimal health.