Does It Work? What Effect Does L-arginine Have On Heart Disease?

BACKGROUND:A reader e-mailed asking whether there were any side effects from taking arginine for high blood pressure.

L-Arginine is an amino acid found in relatively high concentrations in seeds, soy, eggs, nuts, seafood and meats. It was first isolated from lupin seeds, which continue to be used as a source of arginine in animal feed.

Amino acids are the building blocks of proteins. Out of the 20 amino acids needed for almost all proteins, some can be made in the body while those called essential amino acids must be consumed in the diet. Arginine falls in the middle, being called a conditionally essential amino acid. Most of the time, the body makes enough for its needs, but under certain conditions additional dietary arginine may be required.

Arginine is an important source of nitrogen for the body. It is crucial for the body’s synthesis of nitric oxide (NO) – not to be confused with nitrous oxide (N2O), better known as laughing gas. NO plays a number of vital roles in the body, which include relaxing blood vessels, preventing platelet aggregation and having anti-oxidant effects. These discoveries have led to much interest in the role of arginine in promoting cardiovascular health by increasing NO levels.

EVIDENCE FROM STUDIES

In early studies, high doses of L-arginine were given intravenously to examine its effect on growth hormone. Researchers noted that people’s blood vessels dilated after the injections, leading to lower blood pressure. These effects were accompanied by increased blood levels of NO.

However, studies conducted with lower doses of oral arginine had inconsistent results. For example, two separate studies of patients with coronary artery disease found that those taking 6g of arginine per day could exercise significantly better than those taking placebo. Other studies, all relatively small, with patients with various types of heart problems showed similar benefits. In contrast, however, similar studies found no benefits. This became known as the “arginine paradox” – some heart patients benefit quickly and clearly from arginine food supplements, but others do not. One relevant factor seemed to be the stage of heart disease. Patients at early stages of heart disease seemed to benefit more from arginine supplements, while patients already stabilised on optimal medical treatment appeared to benefit little.

Recent research into this paradox has discovered that the body naturally produces substances which counteract arginine’s role in producing NO. These can be elevated in some people with cardiovascular disease for whom supplemental arginine can be beneficial.

PROBLEMATIC ASPECTS

Patients taking arginine in clinical studies had few side effects, with gastrointestinal problems occurring occasionally. Allergies to arginine can occur. Very large doses can lead to vomiting and breathing problems.

One of the largest and longest studies (9g of arginine per day for six months) was stopped after six people died. However, all people in the study had coronary artery disease and thus had some risk of heart problems. An investigation concluded that the deaths couldn’t be clearly related to arginine. However, it does point to the importance of careful monitoring of patients taking arginine for heart disease.

RECOMMENDATIONS

L-arginine is an important dietary amino acid with a role in cardiac health. Research shows that arginine supplements can help some people with heart disease, but not everyone. It appears to be more beneficial at the early stages of heart disease, when some changes are still reversible, but less so when disease has progressed. People stabilised on heart medications also appear to benefit less from L-arginine.

Overall, the evidence points to the importance of careful medical management of heart disease. Before commencing L-arginine for any heart condition, the matter should be discussed with a doctor.

Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University