High blood pressure (hypertension) can limit the flow of blood to vital organs, such as the brain, heart, and kidneys. Long-term constriction of blood flow to the brain, as occurs in many elderly people, may be responsible for a significant loss of cognitive function, ranging from occasional "senior moments" to outright senile dementia. Fortunately, new research from Harvard Medical School shows that reducing blood pressure can improve blood flow to the brain1 and, in so doing, improve impaired cognitive performance.2 While this might seem obvious, many physicians have been hesitant to reduce blood pressure to recommended levels in elderly people with hypertension out of fear that long-term treatment could cut cerebral blood flow too much. But the new findings suggests that this fear is unfounded.1
Hypertension has been called the "silent killer," because — without overt symptoms (i.e., warning) — long-term hypertension can cause subtle damage that eventually leads to heart attack, stroke, dementia, kidney failure, or other devastating events. Hypertension occurs because the arteries that carry oxygen- and nutrient-rich blood from the heart to the rest of the body lose some of their flexibility. So, when the need for more blood increases, and the heart starts pumping more vigorously, the vessels remain somewhat constricted, increasing the pressure inside the arteries and limiting the amount of blood reaching the brain and other target organs. Exactly why hypertension occurs is largely unknown, although it tends to be associated with high cholesterol levels, smoking, obesity, and diabetes.
A group of researchers from Harvard evaluated the effects of conventional antihypertensive medications on blood flow in three groups of people: 1) "normotensives," people with normal blood pressure (<140/90 mm Hg) who were not taking any blood pressure-lowering drugs; 2) "controlled hypertensives," who required medication to keep their blood pressure within the normal range (<140/90 mm Hg); and 3) "uncontrolled hypertensives," whose systolic blood pressure remained >160 mm Hg despite aggressive antihypertensive treatment. Blood flow was measured in the carotid artery, which is located in the neck and serves as the main path blood takes on its way to the brain. Any resistance here restricts the amount of blood available to the brain, starving it of vital oxygen and nutrients and inhibiting its normal functioning.
After 6 months of treatment, using conventional antihypertensive drugs, such as lisinopril and hydrochlorothiazide, the subjects with uncontrolled hypertension achieved a 17 mm Hg decline in mean arterial blood pressure. This reduction was associated with a significant decrease in cerebral vascular resistance (CVR) combined with a significant increase in cerebral blood flow (CBF). CBF changed very little in the normotensive and controlled hypertensive groups. In other words, reducing blood pressure in people with serious hypertension improves the distensibility of their carotid artery, enhancing blood flow to their brain.
While this is certainly good news, antihypertensive drugs are often associated with annoying and/or dangerous side effects, ranging from headache to sexual dysfunction. As a result of these side effects, many people discontinue taking them. The pharmaceutical industry has been looking for safe, effective, tolerable antihypertensives for decades. Needless to say, they're still looking.
Far more preferable would be a natural way of controlling blood pressure that did not cause unpleasant or dangerous side effects. Arginine may be just the thing! Taking supplements of the amino acid arginine has been shown to control blood pressure safely, effectively, and naturally. What's more, in contrast to many conventional antihypertensive medications, arginine may actually enhance sexual function.3
Arginine for Natural Blood Pressure Control
Blood pressure in the brain and throughout the body is controlled largely by the molecules of nitric oxide (NO), a simple gas that performs hundreds of amazing physiological feats. Key among these is the modulation of the tone of the smooth muscles that surround blood vessels. When these muscles constrict, blood pressure rises; when they relax, it falls. The release of NO into vascular muscle cells causes them to relax. In the relative absence of NO, blood pressure goes up.4 By keeping NO levels in balance, the body maintains blood pressure within optimal limits.
Arginine (a.k.a,, L-arginine) works to normalize blood pressure and flow, because it serves as the principal source for molecules of NO. The body utilizes special enzymes (e.g., nitric oxide synthetase, NOS) to convert dietary arginine into nitric oxide. Increasing arginine intake stimulates NO formation and release, which in turn lowers elevated blood pressure, but has no effect on normal blood pressure. In one recent study from Italy, 13 hypertensive patients, who also had angina pectoris (chest pain due to occlusion of coronary arteries), were treated with arginine for 4 weeks. Compared to baseline levels, arginine treatment resulted in a significant decrease in mean systolic blood pressure (from 166 mm Hg to 146 mm Hg) as well as reduced angina and improved quality of life.5
Arginine Reduces Dementia Symptoms
As in other parts of the body, blood flow in the brain is under the control of NO. This is especially important in elderly people, who are most at risk to loss of cognitive function due to poor cerebral perfusion. Concentrations of NO and arginine both decrease with
If hypertension resulting from impaired NO function reduces blood flow to the brain, which can lead to impaired cerebral function, will normalizing NO activity improve cognitive function? According to one small Japanese study,2 it appears that it will.
Figure 1. Cognitive effect of arginine treatment (1.6 g/day) in 16 elderly people (mean age 79). Cognitive function was measured using the revised Hasegawa Dementia Scale (HDS-R). A perfect score = 30; scores <20 (shaded area) indicate dementia. * P <0.0001, 3 Months vs. Baseline and 3 Months vs. Post-treatment. Adapted from Ohtsuka and Nakaya, 2000.
In this study, 16 elderly people with cardiovascular disease (mean age, 79 years), who had been living in a nursing home for 2 to 4 years, were treated with relatively low doses of oral L-arginine (1.6 g/day) for 3 months. Their cognitive function was evaluated using the Hasegawa Dementia Scale (HDS-R) before treatment started, after 3 months of treatment, and finally 3 months after treatment stopped. The HDS-R is a widely used measure in Japan. A score of 30 on the HDS-R is considered normal, while a score of 20 or lower indicates dementia.
After 3 months of treatment with L-arginine, cognitive function improved significantly in all subjects from a mean of 16 to 23 (P <0.0001). Within 3 months of stopping L-arginine treatment, the HDS score returned to pretreatment levels (17) (P <0.0001) (Fig. 1). Lipid peroxide levels (an indicator of oxidative stress) also declined significantly during L-arginine treatment (P <0.001) compared with the Baseline and Post-treatment measurements. The authors hypothesized that L-arginine treatment improved cognitive function by increasing NO levels, by reducing oxidative stress, or both.
There are many good reasons to keep our blood pressure under control; reducing the risk of heart attack, stroke and kidney failure are the most commonly mentioned. Now we know that blood pressure control with arginine may also help preserve our cognitive function.References