Due to high blood pressure, my doctor has recommended I go on a low-sodium diet. So, that got me wondering what it is about sodium that drives this recommendation?
What does sodium do to a body that, by its presence or absence, affects blood pressure in humans?
The basic reason is osmosis, the tendency of solutes to move from an area of high concentration to one of low concentration across a permeable barrier. So, ingesting large amounts of salt results in a high sodium concentration in the blood stream. This in turn causes water to enter the blood vessels by osmosis. More water in the blood means a greater volume of liquid and, therefore, higher blood pressure.
This process occurs primarily in the kidneys, specifically in the part of the nephron called the loop of henle (the image below was taken from wikipedia and is originally from Grey's Anatomy):
With low salt concentrations, water exits the loop and is retained by the body. When sodium concentration is high, the opposite occurs, water enters the blood stream by osmosis and increases blood pressure.
As salt accumulates in thebody, it also indirectly increases the extracellular fluid volume for two basic reasons: 1. When there is excess salt in the extracellular fluid,the osmolality of the fluid increases, and this in turn stimulates the thirst center in the brain, making the person drink extra amounts of water to return the extracellular salt concentration to normal. This increases the extracellular fluid volume. 2. The increase in osmolality caused by the excess salt in the extracellular fluid also stimulates the hypothalamic-posterior pituitary gland secretory mechanism to secrete increased quantities of antidiuretic hormone. The antidiuretic hormone then causes the kidneys to reabsorb greatly increased quantities of water from the renal tubular fluid, thereby diminishing the excreted volume of urine but increasing the extracellular fluid volume. Thus, for these important reasons, the amount of salt that accumulates in the body is the main determinant of the extracellular fluid volume. Because only small increases in extracellular fluid and blood volume can often increase the arterial pressure greatly, accumulation of even a small amount of extra salt in the body can lead to considerable elevation of arterial pressure.
Progressive changes in important circulatory system variables during the first few weeks of volume-loading hypertension.
Salt will cause high blood pressure, but only under certain circumstance.
physiologic hormonal compensations for increased blood volume:
- Atrial natriuretic peptide -- increases sodium excretion, hence this is INCREASED with high blood volume
- Antidiuretic horomone -- ADH increases water reabsorption in the kidney, hence this will be DECREASED with high blood volume
- Renin/Aldosterone -- increases sodium reabsorption from ultrafiltrate back into blood, hence it will be DECREASED
these explainations are a bit reverse (saying that these horomones have these effects and that is why they are released) for the sake of simplicity, and I'm not discussing the mechanism of release of these horomones (aka under what circumstances they are released in the place where they are released from)…
while these horomones help with the kidney regulation of sodium balance and blood volume, this still depends on the kidneys being given the circumstance where they can be effective.
Pathologic circumstances, when elimination of excess sodium fails:
Some people simply have a higher sodium sensitivity and there are a variety of factors that have been statistically correlated to sodium sensitivity, but often the mechanism is unknown. Here are various factors statistically correlated to affect salt sensitivity: http://physrev.physiology.org/content/85/2/679
the above article shows that no organ systems need be compromised for excess sodium to raise blood pressure, but just for the sake of discussing more macroscopic things I want to discuss these organ systems based reasons for the kidney being unable to compensate for excess sodium in the diet=
- The kidney: A patient with renal disease may not be able to regulate the excretion of sodium. Even in normal humans, the kidney's capacity to excrete sodium declines with age, and smaller increases in salt intake induce a rise in arterial pressure, as GFR (the renal filtration of the blood sent to the kidney) falls by about 40%, though individual variations are wide and some people lose less.
Other than the kidney: Other diseases can also interfere with renal excretion of sodium. A problem with maintaining blood volume will cause constriction of the renal artery. This would occur before a drop in blood pressure would occur, as this is a way of preventing a drop in blood pressure. This occurs in congestive heart failure and liver cirrhosis.
- A patient with congestive heart failure may not have adequate renal perfusion. Hence, to maintain adequate blood pressure the renal artery is constricted.
- Also, liver cirrhosis may decrease renal perfusion because of the lack of blood proteins (proteins found inside the blood vessels that keep water in the blood vessels via osmosis) holding fluids in the intravascular space and having them escape into the extra-vascular (outside the blood vessels but still outside the cells of the body) space. Again, to maintain adequate blood pressure the renal artery is constricted.
- burns, also because of loss of blood proteins--> leakage of intravascular fluid to extravascular space--> decreased blood volume and increased sympathetic nervous system output--> reduction of renal blood flow… same as for cirrhosis
In addition to reduction of salt in the diet, diuretics (ex. loop and thiazide) can help the body excrete even more sodium into the urine than what your body can do on it's own.
Diet Sodas, Artificial Sweeteners and Blood Pressure: What Gives?
Many people consider diet soda a good alternative to sugary sodas. After all, it's free of sugar and all its calories. But diet sodas contain a variety of ingredients that may increase your blood pressure or affect your overall heart health. So — it might not be a healthy choice after all.
Higher sodium, lower blood pressure. You read that right.
In another blow against decades of accepted medical wisdom, one of the most prestigious, long-running studies reports that lowering sodium intake doesn’t reduce blood pressure.
The study also implies that most Americans are consuming a perfectly healthy amount of salt, the main source of sodium. But those who are salt-sensitive, about 20 to 25 percent of the population, still need to restrict salt intake.
Consuming fewer than 2,500 milligrams of sodium daily is actually associated with higher blood pressure, according to the Framingham Offspring Study report, given today. The abstract is available at: j.mp/ebsaltr.
The American Heart Association recommends consuming no more than 2,300 milligrams of sodium daily, equal to a teaspoon of ordinary iodized table salt.
High blood pressure is a known risk factor for heart disease and stroke. Hence, lowering salt intake is supposed to lower blood pressure and thus reduce the risk of cardiovascular disease and stroke. But the study found that supposition to be unfounded.
Moreover, the lowest blood pressure was recorded by those who consumed 4,000 milligrams or more a day — amounts considered dangerously high by medical authorities such as the American Heart Association.
Those taking from 2,500 milligrams to 4,000 milligrams a day had very slightly higher blood pressure, but significantly below the low-sodium group. The average American consumes 3,400 milligrams of sodium a day.
Higher levels of calcium, potassium and magnesium were also associated with lower blood pressure. The lowest readings came from people who consumed an average of 3,717 milligrams of sodium and 3,211 milligrams of potassium a day.
The study is an offshoot of the groundbreaking Framingham Heart Study. Both are projects of the National Heart Lung and Blood Institute and Boston University. The new report was funded by the National Dairy Council and the Framingham Heart Study.
The new report was delivered in Chicago during the Experimental Biology meeting by Lynn L. Moore, an associate professor of medicine at Boston University School of Medicine.
The report directly contradicts advice from the American Heart Association, which recommends consuming less than 1,500 milligrams of sodium a day to reduce blood pressure and risk of heart disease.
The American Heart Association justifies its recommendation on a 2001 study in the New England Journal of Medicine . The study is cited in a “scientific statement” by the association.
This story was originally published at 8:30 a.m. Tuesday. It was most recently updated at 2:30 p.m.
The NEJM study examined 412 participants for 30 days. They were randomly assigned to eat either a control diet or the Dietary Approaches to Stop Hypertension (DASH) diet, which is rich in vegetables, fruits, and low-fat dairy products,in persons with and in those without hypertension.
The Framingham Offspring Study based its findings on a population of more than 2,600 men and women, whom it followed for 16 years. That means it can capture the long-term results of salt consumption, which the New England Journal of Medicine study couldn’t do because of its short duration.
Cheryl Anderson, a member of the American Heart Association’s Nutrition Committee, said the study appeared to have some weaknesses in data collection, according to its abstract. Anderson didn’t attend the presentation, because she was delivering her own at the same time.
The best standard for such studies of sodium intake is a 24-hour multiple urine collections protocol, which the study didn’t have, said Anderson, an associate professor in the Department of Family and Preventive Medicine at UC San Diego.
The study used dietary records, which aren’t as accurate as direct measurement, Anderson said.
And it’s also possible that some of those in the study may have changed their sodium intake because they developed high blood pressure, which would confound the correlation, she said.
“When I put it in the broader context of the general literature around dietary sodium assessment and blood pressure, particularly from what we know about clinical trials, (the study) didn’t bother me in any way,” Anderson said.
“Until I see the whole paper, this is not going in any way to disrupt my current thinking around that fact that high sodium intakes are likely to increase your blood pressure.”
Anderson pointed to studies that examined the relationship between sodium intake and the outcome of cardiovascular disease events. These include a study published in the journal BMJ in 2007, led by Nancy Cook of Brigham and Women’s Hospital, Harvard Medical School in Boston.
That study enrolled 744 participants with prehypertension, randomized to either a low-sodium diet or control. It included an original measurement of sodium and subsequent followups.
“The crude rate of cardiovascular disease was somewhat lower among those assigned to the sodium reduction intervention in stratified analysis) than corresponding controls,” the study stated. “After adjustment for baseline characteristics, particularly the imbalance in age, there were significant differences between groups.”
That study began with urinary measurements of sodium excretion, but in the final long-term followup questionnaire, the study used self-reported information on sodium intake.
Anderson said ideally, such studies outcomes would have followed the 24-hour urine collection protocol, but that has proven too difficult. People would need to be monitored for decades to detect the long-term effects of dietary sodium, and that would be prohibitively expensive.
“Are you going to give me money for 25 years to do that?” Anderson asked. “That’s why these studies haven’t been done. It’s because they’re logistically quite a challenge, from a funding perspective almost impossible.”
Moore, who delivered the report at the Experimental Biology meeting, said the putative link between higher sodium consumption, higher blood pressure, and cardiovascular disease and stroke wasn’t well understood. More recent evidence suggests the logic behind that link is flawed.
Early studies found that among those with high blood pressure, restricting sodium lowered blood pressure.
“A low-sodium diet has been popularized for a few decades, and I think it originally had to do with the observation that among people with high blood pressure, if you restrict their sodium intake, their blood pressure actually goes down.”
“I think that led to the inference that restricting your sodium intake in general (among the public) would actually reduce your risk of developing high blood pressure,” Moore said.
Further extrapolating, since higher blood pressure is a risk factor for cardivascular diseases, then lowering sodium would lower blood pressure and hence lower cardiovascular disease rates.
This chain-of-events thinking led to the recommendation that the general population cut its sodium intake. This belief has led to numerous initiatives to lower dietary sodium, including former First Lady Michelle Obama’s campaign to mandate “healthy” changes in school lunches. President Trump reportedly plans to drop some of those restrictions.
Meanwhile, evidence undermined the extrapolation, Moore said. The picture turned out to be much more complicated. People on the lowest-sodium diets actually appeared to have higher cardiovascular risk and risk of dying than those taking more sodium.
“There’s been consequently a lot of controversy over the last five or six years over this topic, but there is a growing body of evidence suggesting that the relationship between sodium and cardiovascular disease is actually J-shaped.”
Moore was referring to a pattern in which an extremely low level of the substance being measured produces a higher risk, which falls to a plateau and then rises again at the higher extreme.
This is the pattern found in an August 2014 study in the New England Journal of Medicine, which found a greatly elevated risk of death or major heart event at the dietary sodium level recommended by the American Heart Association.
The study also found that the average intake for Americans placed them near the bottom of the risk curve.
Anderson, the American Heart Association scientist, said that study was also flawed because it didn’t use a 24-hour urine collection protocol.
Moore said greater attention needs to be given to a hypothesis that people generally consume the amount of sodium they need. In other words, they are biologically driven to keep their consumption within a certain range.
The J-shaped curve implies that tampering with this drive could cause unforeseen health problems.
“There’s evidence that salt restriction has a lot of effects on other systems other than blood pressure,” Moore said. “You end up with higher levels of renin, rather than lower levels,” referring to an enzyme that helps raise blood pressure.
“Other studies have shown that cholesterol goes up, triglyceride levels go up,. So there are a number of effects on known risk factors for heart disease that are independent of blood pressure, that seem to be activated in a setting of salt restriction,” she said.
The 2010 Dietary Guidelines for Americans recommended that sodium intake be lowered to 2,300 milligrams per day for the general population. , The report is a joint project of the U.S. Departments of Health and Human Services and of Agriculture.
However, a 2013 report by the Institute of Medicine specifically declined to endorse that limit, in part because the quality of information was insufficient.
“Overall, the committee found that both the quantity and quality of relevant studies to be less than optimal,” the IOM report delicately stated.
But the carefully worded report also concluded that the bulk of the evidence indicates a correlation between higher levels of sodium intake and cardiovascular disease.
It also said there was insufficient evidence to conclude that lowering sodium intake below 2,300 milligrams per day either increases or decreases the risk of cardiovascular disease or death in the general population.
The 2015 version of the Dietary Guidelines for Americans repeats the recommendation to lower sodium intake to less than 2,300 milligrams.
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How much sodium is too much?
The average American consumes about 1 ½ teaspoons of salt (3,400 milligrams of sodium) a day. Most of this comes from the highly processed foods that we routinely eat. For example, a slice of pizza has approximately 600 milligrams of sodium. A serving of canned chicken noodle soup delivers more than 800 milligrams.
The current Dietary Guidelines for Americans recommend that younger, relatively healthy individuals get no more than 2,300 milligrams of sodium (1 teaspoon of salt) a day, while everyone over age 51 and those with high blood pressure, diabetes, or kidney disease should take in 1,500 milligrams a day. One element of the American Heart Association‘s definition of ideal cardiovascular health is a diet that contains less than 1,500 milligrams of sodium a day. While there is some inconsistency in what the upper daily limit should be, what’s important right now is that most Americans should cut back on the amount of sodium they take in.
Earlier this month, New York City started requiring large chain restaurants to label salty dishes that contain more than 2,300 milligrams of sodium — the upper limit of what you should get over the course of a whole day. The salt-shaker-in-a-black-triangle “sodium bomb” warning is intended to nudge diners toward less salty and presumably healthier dishes.
Avoiding sodium bombs is one way to optimize long-term cardiovascular health. Recent evidence suggests that a single high-sodium meal can temporarily impair blood vessel function. So staying away from high-sodium meals is important for everyone, even for those who don’t have salt-sensitive blood pressure. Cutting down on daily sodium intake requires eating less processed foods and more fresh foods. Food items that contain a lot of sodium include cold cuts, many soups, and condiments such as ketchup and soy sauce.
It will be interesting to see if sodium labels in New York City restaurants will nudge New Yorkers toward healthier choices. Whether or not they do, it’s a good idea for almost everyone to cut back on sodium during the holidays and beyond.
William B. Farquhar, PhD, is professor and chair in the department of kinesiology and applied physiology at the University of Delaware. He studies the role of diet and exercise on human health.
A plant-based diet and hypertension
Hypertension is an insidious, common, and deadly disease, often detected incidentally at a routine doctor's visit or workplace health screening. Worldwide, it is estimated that one billion people have hypertension and approximately 80 million Americans 20 years of age and older are hypertensive.  The National Health and Nutrition Data Examination Survey found that only 54% of hypertensive adults in the United States had their high blood pressure controlled and 17% remained undiagnosed.  These findings translate into poor outcomes as the number of deaths due to hypertension increased by 35% from 2003.  In the Global Burden of Disease 2010 study, hypertension was identified as the number one risk factor worldwide for deaths and disability-adjusted life years.  In the United States, clinic visits, medications and the treatment of complications from hypertension, including heart failure, stroke, and renal disease now account for a substantial portion of the Medicare budget. 
First line therapies for all stages of hypertension include exercise and weight loss.  However, results from one small cross-sectional study suggest that a plant-based diet is the more important intervention. This study compared the blood pressure of sedentary vegans, endurance athletes (matched for body mass index with the vegan group) consuming a Western diet and running an average of 48 miles per week, and sedentary subjects consuming a Western diet. Blood pressure was significantly lower in the vegan group.  Although the benefits of exercise and weight loss seem to be inherently understood by most, the definition and perception of a “healthy” diet is one that has not yet reached consensus.
In the late 1930 s, Dr. Walter Kempner of Duke University introduced the “rice diet” as therapy for renal failure and hypothesized that “we could radically alter the patients' diets and thereby save lives.”  The rice diet was high in complex carbohydrates, consisting mainly of rice and fruit, and low in fat, protein (< 20 g/day) and sodium (< 150 mg/day). He first demonstrated its effectiveness in a diabetic, hypertensive patient with renal and congestive heart failure: post intervention, this patient exhibited decreased cardiac silhouette size as measured by chest X-ray, normalization of a left ventricular strain pattern on ECG, and improvement in hypertensive retinopathy. Similarly, in his first cohort of hypertensive patients, 107 of 192 patients demonstrated marked improvement, including decreased blood pressure, cholesterol levels, retinopathy, and cardiac silhouette size. Despite his findings, Kempner's work was not widely accepted by the scientific community, which favored randomized control trials to substantiate these findings.
The first, major randomized control trial to evaluate diet and hypertension was the Dietary Approaches to Stop Hypertension (DASH) study of the mid-1990s. DASH, a controlled feeding study, examined three different diets: (1) a control diet, representative of a “typical” American diet, (2) the DASH diet, high in fruits and vegetables and low in saturated and total fat, and (3) a diet high in fruits and vegetables but otherwise similar to the control diet. Patients were given standardized meals, and their weight and dietary sodium intake were kept stable.  The DASH diet reduced both systolic and diastolic blood pressure by 5.5 mmHg and 3.0 mmHg, respectively, when compared to control. The diet high in fruits and vegetables but otherwise similar to the control diet also lowered blood pressure but not to the same extent as the DASH diet. The DASH collaborative research group stated that they could not identify the individual components of the DASH diet that made it effective, but other studies have shown that specific components of the DASH diet, such as fruits, vegetables, whole grains, and nuts were each associated with decreased blood pressure.  – 
The Coronary Artery Risk Development in Young Adults (CARDIA) study prospectively followed 5115 young (aged 18 to 30 years), black and white men and women over a 15 year time period and monitored them for the development of cardiovascular disease risk factors.  A CARDIA hypertension sub-study of 4304 subjects revealed a dose dependent inverse relationship between plant-based food consumption, including fruits, whole grains, and nuts, and blood pressure. The opposite relationship was found, however, with meat intake. Greater red and processed meat intake was associated with higher blood pressure. Accordingly, in a cross-sectional analysis of 11,004 British men and women in the European Prospective Investigation into Cancer and Nutrition-Oxford study, among four dietary types: (1) meat eaters, (2) fish eaters, (3) vegetarians, and (4) vegans, the vegans had the lowest prevalence of hypertension. 
Similarly, Borgi, et al.,  found a positive association between animal flesh consumption and hypertension risk in an analysis of three prospective cohorts [Nurses' Health Study I (NHS I), Nurses' Health Study II (NHS II), and Health Professionals Follow-up Study (HPFS)] totaling 188,518 participants with 2,936,359 person-years of follow-up. In this largest prospective study to date on animal consumption and incident hypertension, the positive relationship between animal flesh (including red and processed meat, poultry and seafood) and hypertension was independent of fruit, vegetable, and whole grain consumption. Whereas, red and processed meats were associated with increased hypertension risk in all three cohorts, poultry and seafood intake were correlated with higher rates in two (NHS II, HPFS). The findings of greater animal flesh (red meat, processed meat, and poultry) consumption and increased hypertension risk are consistent with other prospective cohort studies.  –  In the few published prospective studies of seafood consumption and hypertension risk, greater seafood consumption appears either positively associated with hypertension risk or neutral.  ,  , 
The first study to compare blood pressure among habitual vegans, lacto-ovo vegetarians, and non-vegetarians was the Adventist Health Study-2 (AHS-2) calibration sub-study, which included a cohort of 500 mostly white subjects.  Of note, non-vegetarian Seventh Day Adventists tend to consume less meat than persons consuming a typical Western diet.  , 
Nevertheless, the investigators found that vegans and lacto-ovo vegetarians had significantly lower systolic and diastolic blood pressure, and significantly lower odds of hypertension (0.37 and 0.57, respectively), when compared to non-vegetarians. Furthermore, the vegan group, as compared to lacto-ovo vegetarians, not only was taking fewer antihypertensive medications but, after adjustment for body mass index, also had lower blood pressure readings. Another sub-study of AHS-2 examined hypertension in a black population and found that the combined vegetarian/vegan group had significantly lower odds of hypertension (0.56) compared to non-vegetarians. 
Other studies found similar results. In a prospective cohort study of 1546 non-hypertensive subjects followed for three years, those consuming more phytochemical rich foods (plant-based foods) had lower risk of developing hypertension.  In a matched cohort study of 4109 non-hypertensive subjects followed for a median of 1.6 years, vegetarians had a 34% lower risk of developing hypertension than non-vegetarians.  In studies of 5046 and 1615 subjects encouraged to adopt a plant-based diet as part of a health improvement program for 30 days and 7 days, respectively, systolic and diastolic blood pressure fell significantly in both.  ,  In a study of 26 subjects with medically treated hypertension and then placed on a vegan diet for one year, blood pressure fell, and 20 of the 26 subjects were able to discontinue their anti-hypertensive medications.  In a cohort study of 272 non-hypertensive men followed for five years, greater plant protein intake was associated with lower blood pressure.  The totality of evidence taken from these studies indicates that plant-based diets have a meaningful effect on both prevention and treatment of hypertension.
There are a variety of mechanisms proposed by which plant-based nutrition leads to decrease in blood pressure. They include improved vasodilation,  –  greater antioxidant content and anti-inflammatory effects,  –  improved insulin sensitivity,  ,  –  decreased blood viscosity,  ,  altered baroreceptors,  modifications in both the renin-angiotensin,  ,  –  and sympathetic nervous systems,  ,  and modification of the gut microbiota. 
Long-term randomized controlled trials examining the impact of plant-based diets on various health outcomes, including hypertension, will further inform medical guideline creation and refine our understanding of the relationship between diet and disease. However, in lieu of such information and in the context of the data within this Special Issue, we believe that consuming a diet that is mostly or exclusively plant-based appears prudent for the prevention and treatment of hypertension.
What are the benefits of cutting down on sodium?
Eating less sodium can reduce your risk for high blood pressure and bloating,and stave off other effects of too much salt. And did you know that reducing sodium in the food supply could save money and lives?
One estimate suggested that if Americans moved to an average intake of 1,500 mg/day sodium, it could result in a 25.6 percent overall decrease in blood pressure and an estimated $26.2 billion in health care savings.
Another estimate projected that achieving this goal would reduce deaths from cardiovascular disease by anywhere from 500,000 to nearly 1.2 million over the next 10 years.
Finding The Link Between Fat And High Blood Pressure
How fat contributes to high blood pressure is the focus of a new study at the Medical College of Georgia that is part of a National Institutes of Health initiative to understand the relationship between obesity and cardiovascular disease.
"You have obesity and you have hypertension. Where is the link?" says Dr. Gregory A. Harshfield, principal investigator on the $1.4 million grant from the NIH's National Heart, Lung and Blood Institute that will study 160 adolescents, half lean and half overweight or obese, in pursuit of that link. Dr. Paule Barbeau, exercise physiologist, is a co-investigator
Obesity is a risk factor for high blood pressure, which is a major risk factor for cardiovascular disease.
The Augusta researchers and others leaders in the field of hypertension say that obesity may increase pressure by increasing volume rather than constriction.
"We think it's increased volume because of sodium handling," Dr. Harshfield says. "When we put people under stress, the normal response is to increase your blood pressure through vasoconstriction." The kidneys also hold onto sodium to help increase blood volume throughout the body. As the stress ends, so should these normal physiological responses.
But Dr. Harshfield's studies at MCG's Georgia Prevention Institute have shown that some people keep holding onto sodium long after the stress has gone, delaying a process called natriuresis, the body's way of eliminating sodium. His studies have shown this mechanism is impaired in about 30 percent of adolescent blacks and 15 percent of adolescent whites the prolonged, elevated pressures may contribute to the development of hypertension.
Fat, or adipose tissue, was once considered storage material only, says Dr. Barbeau. "Now we realize that it secretes all kinds of substances, such as angiotensinogen (which constricts blood vessels) and leptin. The more fat you have, the more of these substances you make."
And different fat depots secrete different substances. Subcutaneous fat, or fat under the skin, secretes leptin, an appetite suppressant also involved in functions such as reproduction and blood pressure regulation. Visceral fat, packed in and around the organs in the abdominal cavity, secretes angiotensinogen, which makes angiotensin II, a powerful vasoconstrictor that also directs the kidneys to absorb more sodium.
"When you gain weight, leptin is supposed to be secreted by the adipose tissue and that tells your brain, 'Don't eat that much,'" Dr. Barbeau says. "But for some reason, in obese people, that feedback loop doesn't work any more," she says, equating the scenario to a type 2 diabetic's resistance to insulin.
Another leptin-driven system seems to fail as well in the obese and contribute to hypertension. Leptin tells the brain to keep producing the neurotransmitter catecholamine which gears up the stress-triggered sympathetic nervous system. Catecholamine, in turn, is supposed to shut down leptin production, but, inexplicably, that doesn't happen either, says Dr. Harshfield.
The researchers say that stress increases angiotensin II levels and therefore blood pressure. Furthermore, in obese individuals, fat-produced leptin and angiotensinogen keep the blood pressure up by interfering with the natural process of sodium excretion that should occur when the stress is gone. The net result may be early development of hypertension and the damage it causes major organs such as the heart and kidneys.
"How stress interacts with fat in the production of damage to the kidneys is what we are looking at primarily," Dr. Harshfield says. "I think what we are going to see is that in the high-fat kids, the stress will produce greater sodium retention and longer levels of elevated blood pressure."
The MCG researchers began recruiting the 15- to 19-year-olds this fall, a mixture of black and white males and females. Each participant engages in a protocol developed by Dr. Harshfield that includes two hours of rest followed by an hour-long stressful video game, then two more hours of rest. Blood pressure and sodium excretion are measured throughout. Participants are put on a diet for three days prior to the test protocol to regulate their sodium levels. They also get a dual-energy X-ray absorptiometry, or DXA, study to measure body fat, and an MRI at MCG Medical Center to assess visceral fat in the abdominal cavity, as well as studies to look at the size of the heart's pumping chamber and kidney function.
"This is a logical place to go with the work we already are doing," Dr. Harshfield says, which is why he opted to pursue the proposal request from the National Heart, Lung and Blood Institute for novel approaches to help clarify the biologic basis of obesity-related cardiovascular problems such as hypertension and atherosclerosis.
Today more than 60 percent of Americans are either overweight or obese and Drs. Harshfield and Barbeau have seen some of the ill effects in the young people who come to the Georgia Prevention Institute with hopes of being a healthy participant in a study only to learn they already have high blood pressure or other problems.
"This is a highly meritorious application from an established productive (principal investigator) and outstanding investigative team," reviewers of the grant proposal wrote. "The goal of this study is to test a hypothesis that links adolescent obesity to cardiovascular disease through impaired stress-evoked pressure natriuresis. This is an interesting and novel hypothesis, and will be adequately approached by the proposed studies. Whether or not the hypothesis turns out to be correct, important new data will result from the proposed study."
Materials provided by Medical College Of Georgia. Note: Content may be edited for style and length.
Should we all eat less salt?
At an individual level, the benefit of reducing salt on blood pressure may be small. However, at a population level, this small reduction can have a significant benefit on public health. 7 For this reason, reducing salt is encouraged by most dietary guidelines. To reach the 5 g of salt per day recommendation set by EFSA, both individuals and the food industry will need to commit to improving dietary choices and reducing the salt content of products, respectively.
Many EU countries have made progress in industry-led salt reduction campaigns, but more work is needed if we want to reach the target set by EFSA. 8 There also remains some key challenges to help improve public knowledge and awareness on the importance of salt reduction. 9
Salt intake in Europe and across the globe remains well above recommended levels. The high prevalence of high blood pressure and the increased risk of disease it brings emphasises the importance of salt reduction campaigns for both industry and individuals.
High blood pressure and diet
Making changes to your diet is a proven way to help control high blood pressure. These changes can also help you lose weight and lower your chance of heart disease and stroke.
Your health care provider can refer you to a dietitian who can help you create a healthy meal plan. Ask what your blood pressure target is. Your target will be based on your risk factors and other medical problems.
The low-salt Dietary Approaches to Stop Hypertension (DASH) diet is proven to help lower blood pressure. Its effects on blood pressure are sometimes seen within a few weeks.
This diet is rich in important nutrients and fiber. It also includes foods that are higher in potassium, calcium, and magnesium and lower in sodium (salt) than the typical American diet.
The goals of the DASH diet are:
- Limit sodium to no more than 2,300 mg a day (eating only 1,500 mg a day is an even better goal).
- Reduce saturated fat to no more than 6% of daily calories and total fat to 27% of daily calories. Low-fat dairy products appear to be especially beneficial for lowering systolic blood pressure.
- When choosing fats, select monounsaturated oils, such as olive or canola oil.
- Choose whole grains over white flour or pasta products.
- Choose fresh fruits and vegetables every day. Many of these foods are rich in potassium, fiber, or both.
- Eat nuts, seeds, or legumes (beans or peas) daily.
- Choose modest amounts of protein (no more than 18% of total daily calories). Fish, skinless poultry, and soy products are the best protein sources.
Other daily nutrient goals in the DASH diet include limiting carbohydrates to 55% of daily calories and dietary cholesterol to 150 mg. Try to get at least 30 grams (g) of daily fiber.
Check with your provider before you increase the potassium in your diet or use salt substitutes (which often contain potassium). People who have kidney problems or who take certain medicines must be careful about how much potassium they consume.
HEART HEALTHY DIET
Eat foods that are naturally low in fat. These include whole grains, fruits, and vegetables.