L-Arginine Improves Blood Flow and Exercise Capacity
Amino acids perform a dizzying array of functions in the body. They can link together in long chains to form various kinds of proteins, such as enzymes (acetylcholinesterase, e.g., which breaks down the acetylcholine molecule), hormones (insulin, e.g., which regulates blood glucose levels), or structural proteins (collagen, e.g., which gives strength to skin, cartilage, and bone). They can also be converted to amino acid derivatives, such as serotonin, an important neurotransmitter that is derived from tryptophan.
Arginine helps preserve kidney function, boost the immune system, increase insulin sensitivity, promote cardiovascular health, and facilitate erections.
Without question, amino acids are vital for normal body functions and good health – either as individual molecules or in the form of proteins (about 20 different amino acids constitute the tens of thousands of different proteins in our bodies). Some amino acids play more prominent roles than others. Consider, for example, the functions that arginine fulfills in the body. Arginine helps, among other things, to preserve kidney function, boost the immune system, increase insulin sensitivity, and promote a healthy cardiovascular system – and it even helps men to achieve and maintain erections.
Arginine Improves Blood Flow
Many of the benefits derived from sufficient arginine intake stem from its ability to generate nitric oxide in the appropriate tissues, aided by an enzyme called nitric oxide synthase. Nitric oxide (NO) is a very small molecule, and it is highly mobile in moving within and between cells. After its synthesis from arginine, NO acts as a signaling molecule that induces a variety of responses in the body. One of the best-characterized functions of NO is to induce smooth muscle cells to relax.
Smooth muscle cells are found in blood vessels throughout the body (excluding the heart). When these cells relax in response to nitric oxide, the blood vessels expand (a process called vasodilation), blood pressure drops, and blood flow is improved. More blood is delivered to the tissues, which are thus better nourished with oxygen, glucose, and whatever else they may need. Collectively, the physical aspects of blood flow are called hemodynamics, and it could be expected that improved hemodynamics would lead to improved exercise capacity. Let us see about that.
Arginine Reduces Pulmonary Blood Pressure
Studies have demonstrated that oral supplementation with arginine offers substantial improvements in hemodynamics in patients with congestive heart failure (a decline in the heart’s ability to pump blood). Recently, the first study to assess the benefits of oral arginine in patients with pulmonary hypertension was performed.1 Pulmonary hypertension is high blood pressure in the arteries of the lungs.* This is a serious disease resulting from inadequate oxygen exchange between the lungs and the blood. It generally results in low oxygen levels in the blood.
The body has two circulatory systems – one for the entire body except the lungs, and one for the lungs. In the latter (the pulmonary system), blood flows from the heart to the lungs to be oxygenated, and then back to the heart to be pumped throughout the rest of the body.
Diseases such as chronic bronchitis, asthma, and emphysema may impede the flow of air in and out of the lungs (as can obesity), thus making pulmonary hypertension worse over time. These diseases are greatly aggravated, or caused in the first place, by smoking, which is the equivalent of voluntary self-administration of poison.
Supplementation with arginine offers substantial improvements in blood flow, and thus tissue oxygenation, in patients with congestive heart failure.
In the study, 19 patients (4 men and 15 women, average age 49 years) with clinically diagnosed pulmonary hypertension were evaluated to determine the effect of oral arginine supplementation on blood flow. The patients were given a single dose of arginine (0.5 g per 10 kg of body weight – equivalent to 3.5 g for a 70-kg, or 155-pound, person), and their cardiovascular response was measured over the next two hours.
Modest but significant differences were observed in pulmonary blood pressure, which decreased from 53 to 48 mm Hg (millimeters of mercury, the standard unit of measure for blood pressure). In addition, the researchers observed a 16% decrease, on average, in the resistance to blood flow in the arteries of the lungs. Thus, blood flow was substantially improved. Importantly, no changes in heart rate were detected between the treatment and control groups.
Arginine Increases Exercise Capacity
The same group of patients also participated in a separate study to measure exercise capacity (except for three individuals who could not tolerate the maximum exercise level, so 16 patients were left). For one week, nine patients in the treatment group supplemented their diets with 0.5 g of arginine per 10 kg of body weight three times daily (equivalent to 10.5g/day for a 155-pound person), and the other seven patients took placebo. After one week of this regimen, the researchers measured exercise capacity in all the patients by assessing their performance on a stationary bicycle: the patients pedaled at 55 rpm for one minute, and the work rate was increased incrementally until they reached their maximum exercise capacity.
One week of arginine supplementation increased peak oxygen volume by 8% and exercise capacity by 12%.
One of the measurements used in this study was the volume of oxygen consumed by each patient during a one-minute interval (referred to as the peak oxygen volume). Following arginine supplementation for one week, patients increased their peak oxygen volume by 8%, from 831 to 896 ml/min (milliliters per minute). In addition, the patients’ exercise capacity increased by 12%, meaning that they were capable of cycling at a higher resistance level than those in the control group (in whom both of these experimental measures remained unchanged during the study).
Nitric Oxide Reduces Hypoxic Stress
The results described above – improvements in blood flow, blood pressure, and exercise capacity – are believed to be due to the increased synthesis of nitric oxide brought about by arginine. If NO can help alleviate the problem of inadequate oxygen delivery to the body’s cells because of pulmonary hypertension, could it also help in cases of high-altitude hypoxia?
Hypoxia is a lack of oxygen, a condition that can become severe at very high altitudes. A group of researchers from Case Western Reserve University in Cleveland observed that natives of Bolivia and Tibet who live at 3900-4200 meters (12,800-13,800 feet) in the Andes or Himalayas produce higher levels of nitric oxide than Americans who live at low altitudes, near sea level.2 In fact, the Tibetans have nitric oxide levels approximately twice as high as those of lowland Americans. Not surprisingly, the oxygen saturation of their tissues during physical exercise is correspondingly higher at these elevations than it is in low-dwelling, acclimatized non-natives, such as Europeans and Chinese.
Nitric oxide increases hemoglobin’s oxygen-carrying efficiency, thus increasing oxygen delivery to the body’s cells.
Based on these observations, the researchers decided to investigate whether increasing exposure to nitric oxide improves oxygen uptake by the lungs in individuals with artificially induced hypoxia at sea level. They found that as the amount of nitric oxide in the air breathed by the hypoxic individuals increased, so did oxygen uptake (remember, the level of oxygen in the air didn’t change during the experiment, only the amount of nitric oxide the subjects were exposed to).
The researchers suggested that the nitric oxide interacts with hemoglobin in the red blood cells in such a way as to increase its oxygen-carrying efficiency, thus increasing the amount of oxygen that can be taken up and delivered to the body’s cells. This is further evidence of the value of nitric oxide – and hence of arginine supplementation – for improving oxygenation in cases where that is desirable or necessary.