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Why does low Na+ levels cause hypotension (low blood pressure). Alternatively, why does excessive intake of Na+ cause hypertension or high blood pressure?
From what I understand, there are two different mechanisms at play. Renin secretion from kidneys occur during low salt levels in blood and hence, under low sodium concentration, high amount of Renin secretion from kidneys should actually raise the blood pressure, via the Renin-Angiotensin loop, constricting the arteries. Under high sodium concentrations, low renin secretion should be accompanied by low pressure. If the osmotic entry of water into blood raising the blood volume and thus pressure, plays a role here, will not, on increase of blood volume, decreased Vasopressin increase urinary output and thus control the blood volume, not allowing it to cause any body changes? Why isn't the first effect (renin) significant here as compared to the second (osmotic entry).
Renin angiotensin is for regaining homeostasis. If you have lost salts, blood pressure and blood volume will decrease due to loss of fluids. But the renin angiotensin mechanism will try to undo this by stimulating uptake of Na+ and water. But still, they can not fully compensate for loss of Na+, INTAKE of Na+ is NECESSARY.
By the way, the main stimulus for triggering renin angiotensin is Blood volume and pressure rather than Osmolarity of blood. In conditions like hemorrhage where blood loss occurs but there is no change in osmolarity, Renin-Angiotensin will still respond (but ADH(vasopressin) will not as ADH responds only to change in osmolarity.) - biogirl
Alcohol, sodium sensitivity and blood pressure
Alcohol appears to have the potential for both beneficial and toxic effects on the heart. The "French Paradox," for example, refers to the protective properties that red wine may have vis-à-vis heart disease. Chronic heavy drinking, on the other hand, is a leading cause of several cardiovascular illnesses, including high blood pressure. High blood pressure, or hypertension, increases the risk for heart disease and stroke, both leading causes of death in the United States. A study in the December issue of Alcoholism: Clinical & Experimental Research has found that alcohol-induced sodium sensitivity may be one of the mechanisms underlying the association among heavy alcohol consumption, alcohol withdrawal, and high blood pressure.
"We know that chronic exposure to heavy amounts of alcohol elevates blood pressure and contributes to hypertension among alcoholics," said Cristiana Di Gennaro, a junior scientist at the University of Parma and corresponding author for the study. "We also know that sodium sensitivity is characterized by an increase of blood pressure, although not necessarily in the hypertensive range, when salt intake is elevated. In addition, sodium sensitivity has been shown to be an independent risk factor for cardiovascular disease. Our findings indicate that alcohol consumption may raise blood pressure through the induction of a sodium sensitive state."
"There is some evidence that for heavy drinkers, even when they don't drink, blood pressure is high," said Maurizio Trevisan, professor and chairman of the department of social and preventive medicine at the School of Medicine, University of Buffalo. "The day after they drink, for example, their blood pressure may be higher than normal. If they drink chronically, they are in sort of a constant level of withdrawal. This can occur even in people that drink normally, moderate drinkers, although the evidence is not as clear as it is for the heavy drinkers." What happens during these "mini-withdrawals," he said, is even more pronounced during extended or complete withdrawal.
Researchers examined 18 alcoholics (6 females, 12 males) entering in-hospital detoxification at the University of Parma in Italy. Their blood pressure and sodium levels were assessed during their first eight days of stay. During this time, each patient was on a fixed hospital diet that provided 150 mM of sodium per day (considered 'normal'). After one year of carefully monitored abstinence, study participants underwent a four-week phase of examination, which included measuring their blood pressure levels on three separate occasions. Then they were asked to adhere to a diet of 55 mM of sodium per day (considered 'low'), which was later supplemented with 205 mM (for a total of 260 mM, considered 'high') of sodium per day.
During the first eight days of withdrawal, alcoholics on a 'normal' diet of sodium intake nonetheless demonstrated high sodium levels, weight gain, and increased blood pressure. A year later, and during exposure to the dietary sodium manipulations, the same group displayed much more significant changes in blood pressure and greater sodium sensitivity when compared to a group of teetotalers. In addition, changes in blood pressure during the early withdrawal period were related to sodium sensitivity during long-term abstinence. These findings suggest that salt sensitivity plays a key role in blood pressure regulation in early withdrawing alcoholics.
"Prior to this study," said Trevisan, "we knew about some of the conditions that increase sodium sensitivity. One of them is insulin resistance, another is being overweight. Now we have [yet] another factor that appears to increase someone's sodium sensitivity, that is, heavy alcohol consumption. It looks like heavy alcohol consumption for long periods of time appears to derange your sodium metabolism in a way that makes you more sodium sensitive."
"We do not know definitely whether sodium sensitivity is an acquired trait linked to alcohol abuse," added Di Gennaro, "or a genetic trait. "We do know, however, that sodium sensitivity remains significant after at least one year of alcohol abstinence in heavy alcoholics. We believe that our demonstration of an important interaction among alcohol consumption, sodium metabolism, blood pressure regulation and cardiovascular diseases extends further our knowledge about the impact of dietary and lifestyle factors on one of the most important causes of morbidity and mortality in western countries. Our findings also suggest that a dietary reduction of both alcohol and salt is warranted."
Trevisan agrees. "Everybody should benefit from a low-sodium diet anyway," he said.
Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.
The Secret Weapon Against High Blood Pressure
When it comes to high blood pressure, sodium seems to get all the attention. Cutting out salt is likely the first advice your doctor will offer if your numbers are high.
Sodium raises your blood pressure by pulling water into your blood vessels. This raises your total blood volume which, in turn, increases your blood pressure. Reduce your sodium and you lower your blood pressure.
But that’s easier said than done.
Many people struggle to stick to a low-sodium diet because everything ends up tasting so bland.
They may not know that there’s another side of the blood pressure equation. Most doctors don’t mention it. It’s potassium.
Sodium and potassium are the yin and yang of blood pressure. While sodium makes you retain water, potassium pulls water out. That lowers blood pressure.
It’s a process known as the sodium-potassium pump. When sodium moves out of a cell, potassium moves in. And vice versa.
When you get more potassium, it actually flushes sodium out of your body.
That means the key to healthy blood pressure isn’t low sodium, as you may have been told. It’s the balance between sodium and potassium that matters.
Why Caveman Had Healthy Blood Pressure
Thousands of years ago, when our caveman ancestors were hunter-gatherers, potassium was abundant. But sodium was scarce.
The Paleolithic diet delivered about 11,000 mg of potassium a day, but only about 700 mg of sodium. Our bodies evolved to operate at their peak when they get far more potassium than sodium.
But today, most of us get more sodium in our diets than potassium. The average American consumes between 2,500 and 7,500 mg of sodium a day. And we get only about 2,500 mg of potassium a day.
The result? High blood pressure.
The USDA recommends a daily potassium intake of 4,700 mg. Fewer than 2% of Americans achieve that.
You can eat less salt—if you like bland food. Or you can increase your potassium levels. Many fruits and vegetables have high levels of the mineral.
Top 7 Foods High in Potassium
Seven great sources of potassium are:
- Avocado. One avocado has about 975 mg of potassium.
- Tomato sauce. One cup has 728 mg.
- Watermelon. Two medium-sized wedges have 641 mg.
- Winter squash. One cup of butternut squash gives you 582 mg.
- Sweet potatoes. One sweet potato has 542 mg.
- Spinach. A cup of frozen spinach has 540 mg.
- Beets. One cup gives you 518 mg.
You’re probably wondering why we haven’t mentioned bananas. They are perhaps the food best known for being high in potassium. A medium-sized banana has 422 mg of potassium. That’s significantly less than the foods above.
You may also wonder why we don’t recommend supplements.
It’s because potassium supplementation can be tricky. If you take too much, it can trigger heart rhythm problems.
For this reason, the FDA limits potassium supplements to only 100 mg per pill. You would have to take 47 pills to get the recommended amount.
It’s best to stick to foods to get the potassium you need for healthy blood pressure readings.
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Sodium Intake and Hypertension
The close relationship between hypertension and dietary sodium intake is widely recognized and supported by several studies. A reduction in dietary sodium not only decreases the blood pressure and the incidence of hypertension, but is also associated with a reduction in morbidity and mortality from cardiovascular diseases. Prolonged modest reduction in salt intake induces a relevant fall in blood pressure in both hypertensive and normotensive individuals, irrespective of sex and ethnic group, with larger falls in systolic blood pressure for larger reductions in dietary salt. The high sodium intake and the increase in blood pressure levels are related to water retention, increase in systemic peripheral resistance, alterations in the endothelial function, changes in the structure and function of large elastic arteries, modification in sympathetic activity, and in the autonomic neuronal modulation of the cardiovascular system. In this review, we have focused on the effects of sodium intake on vascular hemodynamics and their implication in the pathogenesis of hypertension.
Keywords: arterial stiffness endothelial function hypertension salt intake salt-sensitivity sodium intake sympathetic activity.
Conflict of interest statement
The authors declare no conflicts of interest.
Relationship between high salt intake…
Relationship between high salt intake with diet, blood pressure, and arterial stiffness. Abbreviations:…
How Much Salt?
According to the American Association of Kidney Patients, lower salt usage means lower blood pressure. The association recommends less than 5g, or 100 nanomols of sodium daily, which translates into 2,300 mg per day. According to the Cleveland Clinic, salt should be restricted to no more than 1,500mg, which is considerably less—this recommendation originated with the American Heart Association. One teaspoon of salt contains about 2,400mg of sodium. Foods such as bacon, sausage, canned soups, snack foods and pickled foods all tend to be high in salt the Cleveland Clinic recommends you do not eat them if you have high blood pressure.
More than just raising blood pressure pursuant to accumulated body fluids, very low blood sodium levels and the resulting chemical imbalance in your blood can cause confusion, headaches, nausea or even coma and death. A moderate to low sodium diet helps protect you from the chronic conditions caused by too much sodium, including high blood pressure, blood vessel disease, and heart and kidney failure. The 2010 Guidelines for Americans recommends a maximum daily sodium intake of 2,300 mg for healthy adults under 51 years of age, and less than 1,500 mg for anyone 51 or older, who is sodium-sensitive or has existing conditions, such as heart or kidney disease.
The Facts on Sodium and High Blood Pressure
Everybody has sodium in their diet it's a fact of life. Sodium is an essential nutrient. Some of us, however, may be getting too much, and often we aren't even aware of where it's hiding in the foods we're eating. Learn why lowering your sodium intake may benefit your health.
Sodium Intake Adds Up
The good news first: Salt has many uses. It raises the boiling point of water, tenderizes meats and enhances the flavor of many foods. The bad news is that table salt contains 2,300 milligrams of sodium per teaspoon. For most people and children 14 years and older, the recommendation is to limit sodium to less than 2,300 milligrams per day. For those with existing blood pressure or other health concerns, the recommendation may be even lower. According to the Dietary Guidelines for Americans, children ages 1 through 3 are recommended to limit sodium intake to 1,200 milligrams per day 1,500 milligrams per day for children ages 4 through 8 and 1,800 milligrams per day for ages 9 through 13.
It would be difficult to consume that much sodium in one concentrated bite. Instead, sodium intake adds up throughout the day. And based on estimates by the Centers for Disease Control and Prevention, only a small amount of the average Americans' daily intake comes from adding salt to food at the table. Salt in processed and ready-to-eat foods delivers the majority of sodium in our diets.
Sodium is prevalent in many of the foods we eat and in excess can be harmful to our health. However, a number of studies show that decreasing sodium intake can lower blood pressure. Consuming less than 2,300 milligrams of sodium per day for adults can have an additional impact of lowering blood pressure, especially when combined with the Dietary Approaches to Stop Hypertension, or DASH, eating plan, a fruit and vegetable-centered diet that is lower in sodium and fat. Good sources of potassium &mdash an important mineral of the DASH diet which has been shown to help decrease blood pressure &mdash include potatoes, sweet potatoes, squash, beans and orange juice.
Sodium's Hidden Sources
Beware: Sodium isn't only in salty snacks or the table shaker. Many of the already prepared foods and meals you consume at restaurants, cafes and grab-and-go items at grocery stores have sodium, because it's an inexpensive way to add flavor and is an effective way to preserve foods. Even foods with low to moderate sodium content can lead to a high sodium diet if you consume too much of them.
Topping the list for highest percentage of our daily sodium consumption are items such as bread, cold cuts and cured meats, pizza, fresh and processed poultry, soups, sandwiches (including burgers), cheese and pasta.
How to Reduce Sodium Intake
The best way to combat high sodium in your daily diet is to watch your intake of highly processed foods. Read the Nutrition Facts label and look for the Daily Value of sodium in the foods you eat. And consider these satisfying options to keep sodium under control: fruits and vegetables, unsalted nuts, legumes and whole grains (including brown rice, oats and barley).
Sodium sensitivity and blood pressure
Many people still believe that salt intake is the main culprit in high blood pressure, but even the American Heart Association has moved on from this myth.
Hypertension is a serious and dangerous condition of elevated blood pressure, and an indication that something is out of balance. One-third of the world’s population has high blood pressure, which is responsible for almost 50 percent of cardiovascular deaths. Normal pressure is considered less than 120 mmHg systolic and 80 mmHg diastolic (120/80) that level and above is abnormal. Prehypertension is considered 120-139/80-89, and hypertension above that level.
Elevated blood pressure is part of the chronic disease model, whereby excess body fat promotes chronic inflammation and carbohydrate intolerance, leading to poor health and fitness, including hypertension. In some cases, h ypertension may be a side-effect of various drugs including NSAIDS (non-steroidal anti-inflammatory drugs), oral contraceptives, sympathicomimetics, anti-migraine and anti-dementia drugs, corticosteroids, antidepressants, antineuropathic, drugs for epilepsy, Parkinson’s disease, and others.
In most cases, improving lifestyle can reduce abnormally elevated blood pressure to normal without the need for medication — this is recommended as the first approach to treatment. Reducing excess body fat, typically caused by carbohydrate intolerance and corresponding elevations of insulin, often can bring desirable results relatively quickly, as this may be the most common cause of hypertension. This means eliminating all refined carbohydrate, especially sugar, from the diet.
During the Two-Week Test when carbohydrate intake is very low, elevated blood pressure may reduce rapidly, with those on medication potentially developing abnormally low blood pressure (hypotension), which can be dangerous. Asking your health practitioner to monitor your blood pressure during these lifestyle changes is important. In some people, blood pressure adaptation may take longer.
Just how long it takes for blood pressure to normalize, of course, depends on the individual. In short, those who become healthier and fitter sooner can reduce high blood pressure faster. In those with chronic inflammation, arterial stiffness — hardening of the arteries, or arteriosclerosis — often develops, which can make reductions in blood pressure a slower process, taking weeks, months, or longer (especially in those with diabetes or other diseases). Regular monitoring, especially when on medication, is essential.
Most sodium consumed is sodium chloride found in various types of salt. While sodium is an important nutrient, one of the key electrolytes we all require, when the body’s hormones and other metabolic balance is off, too much sodium can raise blood pressure due to a condition called sodium sensitivity. But like other causes of hypertension, probably most cases can be remedied with a healthy lifestyle.
While those who have sodium sensitivity don’t usually feel it, this condition can sometimes manifest as slightly tight or swollen fingers after exercise, or excess water weight. There is no laboratory test for sodium sensitivity, but a dietary sodium challenge can help you discover if you’re sodium-sensitive. This would be indicated by a change in blood pressure of 5-10 percent (or at least 5mmHg) in response to a change in sodium chloride intake.
The chart below is an actual example of what can happen in a sodium-sensitive person during this challenge — blood pressure quickly trends downward when sodium is restricted from the diet, and rises when added back. During sodium restriction, the use of sodium chloride salt is avoided, along with high-sodium foods, which, in addition to most packaged and fast foods, includes smoked, cured, and salted meats and fish such as bacon and other sliced meats, and sardines, caviar and anchovies. The use of potassium chloride salt (also called salt substitute), which is low in sodium, is allowed in moderation.
Sodium sensitivity can develop for various reasons:
- Dysfunction of the sodium-regulatory mechanisms, particular in the kidneys, and the adrenal hormone aldosterone. This can be triggered by excess stress, raising the hormone cortisol.
- Excess body fat and associated chronic inflammation and carbohydrate intolerance (insulin resistance), which can create stress, and raise insulin, causing arterial stiffness, not allowing vessels to expand properly, raising blood pressure.
- A genetic mutation that can cause sodium sensitivity can adversely affect sodium metabolism and mechanisms affecting dilation of the arteries.
In addition, smaller numbers of people with normal blood pressure can be sodium-sensitive, a problem that can increase the risk for cardiovascular disease, asthma, osteoporosis, stomach cancer and kidney problems. Determining this sensitivity requires more complex assessments.
The recent recommendations by the Institute of Medicine for sodium chloride salt intake is up to 5.8 g (2.3 g, or 2300 mg, of sodium) for younger adults, a bit less for older adults. This is just over one teaspoon of salt daily. This amount of sodium would be too much for a person performing a sodium challenge.
Contrary to conventional wisdom, sodium deficiency is a frequent problem as well. It’s called hyponatremia, and is 10 times more common than heart attacks. In addition, writing in the journal Current Opinion in Nephrology and Hypertension (2013 Diagnostic tools for hypertension and salt sensitivity testing), Robin Felder and colleagues state that “ a low-salt diet may not be beneficial to everyone and may paradoxically increase cardiovascular risk by raising blood pressure in some individuals.” This problem is called inverse salt sensitivity.
Athletes, and others who sweat a lot, may be more susceptible to increased sodium loss (sweat contains high amounts of sodium and little potassium). Increased high-intensity training can also cause excess sodium loss through the urine due to hormone imbalance.
Reducing blood pressure naturally by improving overall health can help other accompanying health issues, and is the first line of treatment. This is directed at reducing and maintaining body fat to normal levels, which reduces carbohydrate intolerance and insulin, something most easily accomplished by avoiding junk food, especially sugar and other refined carbohydrates. Improving health to lower blood pressure is usually effective enough to avoid or eliminate medication. In some cases, this may mean reducing sodium intake to levels that don’t raise blood pressure (see chart).
Once again, for those already on prescription drugs for high blood pressure, getting your health practitioner’s help is important for careful monitoring and reducing or eliminating medication as needed. This is important, as better eating can reduce blood pressure, and medication continues doing the same. Lowering blood pressure too much with medication is dangerous it can impair health, especially for the brain.
Studies have demonstrated the benefits of improved lifestyle for optimal health and fitness, and addressing hypertension is no exception. In difficult cases, sodium sensitivity should also be considered.
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Funding: NIH’s National Heart, Lung, and Blood Institute (NHLBI) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) German Federal Ministry for Economics and Technology/DLR Forschung unter Weltraumbedingungen American Heart Association Renal Research Institute TOYOBO Biotechnology Foundation Interdisciplinary Center for Clinical Research Erlangen and Deutsche Forschungsgemeinschaft.