Blood pressure and table salt

[John Bentley]

I read an article in the local newspaper today about preventing high blood pressure by lowering your salt intake. Now I am a veterinarian, and we get extensive education in animal physiology in veterinary school, or at least the one I attended. I have always heard that you could lower your risk of high blood pressure by lowering your salt intake, but I cannot see how that is possible if you have a normal heart, lungs, adrenals, and kidneys. Can someone explain how a healthy person can prevent high blood pressure by lowering salt intake? I tend to think it's one of those medical "facts" that has been accepted without being looked at too carefully.

[Pantastic]

I would say it is like diabetes. No no, stay with me.
A high sugar intake would not give you diabetes, but if you already had it, it would make it worse.
In a similar way, high salt intake would not give you high BP, but if your kidneys were not working properly, it would push up your blood pressure.

Key point here, many people don't know they have diabetes or high BP. So, on balance, maybe it's better to have a low salt diet cos you never know if your kidneys are working propa or not.

[Pragmatist]

Originally posted by John Bentley
I read an article in the local newspaper today about preventing high blood pressure by lowering your salt intake. Now I am a veterinarian, and we get extensive education in animal physiology in veterinary school, or at least the one I attended. I have always heard that you could lower your risk of high blood pressure by lowering your salt intake, but I cannot see how that is possible if you have a normal heart, lungs, adrenals, and kidneys. Can someone explain how a healthy person can prevent high blood pressure by lowering salt intake? I tend to think it's one of those medical "facts" that has been accepted without being looked at too carefully.

Doesn't blood pressure regulation have something to do with sodium/potassium ratio? I may be wrong about that, but I always assumed that it was the ratio of sodium to potassium intake that was important, and that the advice about lowering salt was just a misinterpretation of the idea of decreasing sodium intake and increasing potassium intake in a typical western diet.

It's not an area I know a lot about, so I may be completely wrong. It would be interesting to know if its true.

[Diogenes]

Originally posted by Pantastic
I would say it is like diabetes. No no, stay with me.
A high sugar intake would not give you diabetes, but if you already had it, it would make it worse.
In a similar way, high salt intake would not give you high BP, but if your kidneys were not working properly, it would push up your blood pressure.

Key point here, many people don't know they have diabetes or high BP. So, on balance, maybe it's better to have a low salt diet cos you never know if your kidneys are working propa or not.

Riiiiiiiight.. Supersize my order, but no salt please. I'm trying to watch my BP.. :D

( Guess what? It ain't the salt..;) )

[John Bentley]

Originally posted by Pantastic
I would say it is like diabetes. No no, stay with me.
A high sugar intake would not give you diabetes, but if you already had it, it would make it worse.
In a similar way, high salt intake would not give you high BP, but if your kidneys were not working properly, it would push up your blood pressure.

Key point here, many people don't know they have diabetes or high BP. So, on balance, maybe it's better to have a low salt diet cos you never know if your kidneys are working propa or not.

Ok, admit it. You've been reading Kumar's post, haven't you?

No, I understand your point, but the newspaper article specifically stated that lowering salt intake would help prevent high blood pressure (along with weight reduction, exercise, quitting smoking, etc.).

What made me post the thread was that after reading the article, I had a discussion with my wife (also a vet) about the assumption by most people that high salt in your diet will cause your blood pressure to rise. My contention is that people who have normal sodium metabolism, uptake, and excretion can eat as much sodium as they want, and it will not put them at risk for high blood pressure. She says it will, I say it won't. Anybody else want to chime in and help settle the dispute?

[John Bentley]

Originally posted by Pragmatist
Doesn't blood pressure regulation have something to do with sodium/potassium ratio? I may be wrong about that, but I always assumed that it was the ratio of sodium to potassium intake that was important, and that the advice about lowering salt was just a misinterpretation of the idea of decreasing sodium intake and increasing potassium intake in a typical western diet.

It's not an area I know a lot about, so I may be completely wrong. It would be interesting to know if its true.

Actually, blood pressure regulation is incredibly complex, and involves lots of different sensors and organs and hormones in your body. It does involve exchanging K for Na in the kidney tubules as part of the Na/K regulation. However, I would think that your intake of K would have to be artificially lowered with drugs (some diuretics do that), or intentionally lowered with diet before it would get so low that you have problems with it. It is the main intracellular ion so you get lots of it with any diet that includes cellular material. I can't think of any diet that doesn't include that off the top of my head.;)

[pupdog]

I've read that the foreign-diet studies that purported to show lowering sodium intake reduced odds of hypertension, but that another look at the data suggested those diets may have worked because they contained relatively higher amounts of calcium. This was reported in

Gary Taubes, 1998, The (political) science of salt: Science 281(5379):898-907 and some updated information in Science 288(5470):1319.

The controversy was unsettled at the time of the later article.

[Dr. Imago]

Originally posted by John Bentley
My contention is that people who have normal sodium metabolism, uptake, and excretion can eat as much sodium as they want, and it will not put them at risk for high blood pressure. She says it will, I say it won't.

[ANECDOTE ALERT]

I'm 36-years-old, I have hypertension in my family history, I eat an absolute boat-loads of salt everyday, I exercise regularly (weights and aerobics), my BMI is about 23.1, and I currently have no major health issues going. My BP, which I regularly measure, is always 120-130/70-80.

[/ANECDOTE ALERT]

I still would not recommend eating a lot of salt, though, especially if you have CHF or other cardiac problems. Fact is, 90% of people diagnosed with hypertension is deemed to be "essential", which means we "essentially" don't know what causes it.

Check out this study (http://allhat.sph.uth.tmc.edu/) for what's currently considered to be the definitive info on the matter.

-TT

[Pragmatist]

Originally posted by John Bentley
Actually, blood pressure regulation is incredibly complex, and involves lots of different sensors and organs and hormones in your body. It does involve exchanging K for Na in the kidney tubules as part of the Na/K regulation. However, I would think that your intake of K would have to be artificially lowered with drugs (some diuretics do that), or intentionally lowered with diet before it would get so low that you have problems with it. It is the main intracellular ion so you get lots of it with any diet that includes cellular material. I can't think of any diet that doesn't include that off the top of my head.;)

Breatharian? :D

Seriously, thanks John.

[Dr. Imago]

I should clarify something...

If you have been diagnosed with hypertension, there is a clear benefit to reducing your sodium intake. Reducing your diet to total 2.4g of elemental sodium per day from all sources (or, roughly 5 gms of NaCl) results in a reduction of systolic blood pressure.

We're talking about sodium causing hypertension, which I don't think is the case.

-TT

[Rolfe]

I know this is my subject, but there's a reason for my silence on this particular point. I have a professor friend (Bob Michell, BSM) who has written extensively on exactly this matter, and every time I think I've got my head round what he said, it all evaporates again. Total blind spot. I'm sure if we could lure Bob here he'd explain it all though....

Rolfe.

[John Bentley]

Originally posted by Rolfe
I know this is my subject, but there's a reason for my silence on this particular point. I have a professor friend (Bob Michell, BSM) who has written extensively on exactly this matter, and every time I think I've got my head round what he said, it all evaporates again. Total blind spot. I'm sure if we could lure Bob here he'd explain it all though....

Rolfe.

Come on Rolfe, don't be chicken. Of course, if I'm wrong, I'll never hear the end of it from my wife. Again, as ThirdTwin carefully pointed out, I am saying that high sodium intake cannot predispose you to hypertension assuming you are healthy, and have a normal Na metabolism.

I want to hear from Rolfe. Rolfe. Rolfe.

[epepke]

Originally posted by John Bentley
I read an article in the local newspaper today about preventing high blood pressure by lowering your salt intake. Now I am a veterinarian, and we get extensive education in animal physiology in veterinary school, or at least the one I attended. I have always heard that you could lower your risk of high blood pressure by lowering your salt intake, but I cannot see how that is possible if you have a normal heart, lungs, adrenals, and kidneys. Can someone explain how a healthy person can prevent high blood pressure by lowering salt intake? I tend to think it's one of those medical "facts" that has been accepted without being looked at too carefully.

Some individuals are salt-sensitive. Most people are not.

[Bruce]

The body does what it can to maintain a consistent sodium concentration. When you take in excess sodium, the body sends a message to the (stomach, intestines?) to retain water in order to restore the concentration. The increased water rentention also aids the kidneys in filtering and flushing the excess sodium, however, tissues throughout the body swell because of the increased water and constrict blood vessels, raising the blood pressure.

The whole cycle can be prevented by lowering your sodium intake, but what always bothered me was how much do you lower it? Low sodium levels are much more devastating than excess. It causes blackouts, nervous system damage, and coma's. That's why doctors want you to drink Gatorade (salt water) when you are dehydrated. If you work out a lot, you need to keep you sodium level up because you sweat out even more sodium than you urinate.

I believe there are safer ways to lower your blood pressure than tampering with your sodium intake. There was a huge, unfounded fear of sodium that turned into mass hysteria in the '80's that is still passed along as rhetoric today. Notice that nobody uses the word "salt" anymore. Today it's called "electrolytes".

[John Bentley]

Originally posted by Bruce
The body does what it can to maintain a consistent sodium concentration. When you take in excess sodium, the body sends a message to the (stomach, intestines?) to retain water in order to restore the concentration. The increased water rentention also aids the kidneys in filtering and flushing the excess sodium, however, tissues throughout the body swell because of the increased water and constrict blood vessels, raising the blood pressure.

The whole cycle can be prevented by lowering your sodium intake, but what always bothered me was how much do you lower it? Low sodium levels are much more devastating than excess. It causes blackouts, nervous system damage, and coma's. That's why doctors want you to drink Gatorade (salt water) when you are dehydrated. If you work out a lot, you need to keep you sodium level up because you sweat out even more sodium than you urinate.

I believe there are safer ways to lower your blood pressure than tampering with your sodium intake. There was a huge, unfounded fear of sodium that turned into mass hysteria in the '80's that is still passed along as rhetoric today. Notice that nobody uses the word "salt" anymore. Today it's called "electrolytes".


Wow, Bruce. Sorry Dude, but all of the above is just...well...wrong. Or at the least, skewed. I therefore invoke the Minor Deity (MD for short) Guyton to smite you with his sacrosanct physiology textbook.

[Hellbound]

Have to agree with John there.

Most Doctors will not tell you to drink Gatorade when dehydrated...they'll tell you to drink water. Regular water is absorbed into he tissues faster. The only time you'd want Gatorade (or more correctly, Lactated Ringer's IV) is if the person was drinking too much water and/or skipping meals, resulting in a loss of electrolytes.

Eating regular meals provides enough electrolytes (of which sodium is one) to allow function even under desert conditions. Typical fluid for rehydration is Normal Saline, which does have a small amount of salt in it. The salt is not to replace lost electrolytes, though, it's there to match the salt concentration of the fluid to that of the body (about .7% IIRC). This also allows for faster absorbtion.

Edited to add:

Not to mention the excessive amounts of sugars and carbohydrates in Gatorade, which all require additional water for the body to process. If dehydrating, sit in the shade, loosen clothing, and drink cool (not cold) fluids slowly if possible (nausea sometimes prevents fluid intake, requiring IV therapy).

[Bruce]

Originally posted by John Bentley
Wow, Bruce. Sorry Dude, but all of the above is just...well...wrong. Or at the least, skewed. I therefore invoke the Minor Deity (MD for short) Guyton to smite you with his sacrosanct physiology textbook.

When I originally wrote that, it started with "I'm a chemist, not a physiologist, but here's my half-assed guess:"

By the time I finished, I decided to remove the first sentence to see if I could impress anyone, just in case I guessed correctly. Alas, I guessed incorrectly and likely planted a seed of ignorance that will spread across the world by word-of-mouth until it's accepted as general knowledge.

My PhD powers are growing! Now all I need is some little round glasses and a goatee, then everyone will be too intimidated to argue with me. MWahahahaa.

The only people that can stop me are here on this forum.

You all have to sleep sometime, my pretties, and I'm still relatively young. :D

[John Bentley]

Originally posted by Huntsman
Have to agree with John there.

Most Doctors will not tell you to drink Gatorade when dehydrated...they'll tell you to drink water. Regular water is absorbed into he tissues faster. The only time you'd want Gatorade (or more correctly, Lactated Ringer's IV) is if the person was drinking too much water and/or skipping meals, resulting in a loss of electrolytes.



Just a mild quibble. The fluid of choice depends on the reason for dehydration. Different fluids would be needed for say, sweating, as opposed to vomiting, as opposed to diarrhea. Each type loses its own set of electrolytes that need replacement. And dietary changes such as drinking too much water or skipping meals would be unlikely to alter the blood's electrolyte balance unless taken to disease type extremes, such as diabetes insipidus (having to do with a hormone in the hypothalamus that controls water regulation in the kidneys, not sugar regulation) or complete starvation.

As my original premise states, I'm pretty sure that anyone with a normal blood pressure regulation system, healthy organs, etc., can eat a high salt diet without predisposing themselves to high blood pressure. Am I right? Or does my wife get gloating rights?

[yersinia29]

I'm no medical expert, but I think you guys are making this too complicated.

When sodium gets into your bloodstream, it draws water from the surrounding tissues to maintain the proper osmotic balance.

When water enters your bloodstream, it causes increased blood pressure because the blood vessels are carrying more fluid in a fixed space than they were previously.

[John Bentley]

Originally posted by yersinia29
I'm no medical expert, but I think you guys are making this too complicated.

When sodium gets into your bloodstream, it draws water from the surrounding tissues to maintain the proper osmotic balance.

When water enters your bloodstream, it causes increased blood pressure because the blood vessels are carrying more fluid in a fixed space than they were previously.

You would think it would be simple, wouldn't you? But this is where mammalian (at least land based mammals - which is all I really know a lot about) is so utterly cool. The body has so many incredible feedback and backup systems, to handle problems like this. When your fluid volume expands, baroreceptors in your carotid arteries and kidneys initiate a cascade of events that keep the blood pressure within narrow limits until the excess fluid can be dumped by the kidneys.

First, your heart rate slows and heart muscle contraction force goes down. The venous and lymphatic components of your vasculature expand to accomodate the extra fluid. In response to a hormone released from the kidneys (and subsequently converted to another form in the lungs - don't ask me why), the muscles in the walls of small arteries relax, the arteries expand, thus further expanding the available intravascular fluid space and making it easier for the heart to pump the blood around without raising the pressure. All of this happens within seconds to minutes after the baroreceptors detect an increase in blood pressure. In other words, the vascular space is not fixed, but is in fact very dynamic and changes rapidly from second to second. For more long-term control (on the order of minutes to hours), your kidneys dump the excess fluid and excess salt. This is, in part, a response to a hormone that was released from your hypothalamus as soon as a rise in blood pressure was detected.

Believe it or not, that's a greatly over-simplified version of blood pressure control. The body is just such an amazing, self-regulating machine. It's so complex, that it's amazing it works at all, and that it can handle such a wide range of damage. Evolution rocks!

[TillEulenspiegel]

I don't think theres any study that shows that sodium is the primary cause of hypertension. A more complete picture of a subject would probably revel that they engage in other lifestyle choices that demonstrate a propensity for causing hypertension. Those being that their diet and exercise regimen are probably not the ideal. Like a high fat diet , which is more then understandable in todays society and a less then active exercise routine.

So many factors have an impact on the overall health of the subject, but I believe that sodium intake can be adjunctivley causal, over a period of time in concert with other factors. The fact that after diagnosis it is wise to mantain a lower salt intake then before.

[Camillus]

I can remember one of my physiology lecturers bemoaning the complexity of BP control and our lack of understanding of it. He seemed to think the evidence suggested that salt had no impact on your BP until you hit about 50 and then it might contribute to hypertension in some people.

[Rorimack]

Originally posted by John Bentley
[B]You would think it would be simple, wouldn't you? But this is where mammalian (at least land based mammals - which is all I really know a lot about) is so utterly cool. The body has so many incredible feedback and backup systems, to handle problems like this. When your fluid volume expands, baroreceptors in your carotid arteries and kidneys initiate a cascade of events that keep the blood pressure within narrow limits until the excess fluid can be dumped by the kidneys. (...)

You would think it would be _that_ simple, wouldn't you? ;)

What you have written is true: it is the typical reaction if the blood pressure increases temporary.

But if this increase is continous (like eating a salt-rich diet), then the receptors simply adjust their sensitivity to the new standard. Because of this resetting, a chronical increase of blood pressure doesn't mean that the chemoreceptors constantly detect it as "high blood pressure".

[materia3]

Some us seem to be talking ourselves out of low salt intake to lower blood pressure particularly if we are hypertensive although recent findings are bringing back the older notions that sodium restriction can help prevent HTN as well. Over the past two or three years there has been some impressive research under the acronym DASH (Dietary Approaches to Stop Hypertension) which can be accessed in MedLine and elsewhere that may be worth a look.

Here's part of one recent abstract:

Am J Cardiol. 2004 Jul 15;94(2):222-7.


A further subgroup analysis of the effects of the DASH diet and three dietary sodium levels on blood pressure: results of the DASH-Sodium Trial.

Bray GA, Vollmer WM, Sacks FM, Obarzanek E, Svetkey LP, Appel LJ; DASH Collaborative Research Group.

Pennington Biomedical Research Center, Baton Rouge, Lousiana, USA. brayga@pbrc.edu

This study presents an extensive analysis of the effects on blood pressure (BP) of changes in sodium intake over a wide array of subgroups, including joint subgroups defined by age and hypertension status, race or ethnicity and hypertension status, and gender and race or ethnicity. Participants were given 3 levels of sodium (50, 100, and 150 mmol/2,100 kcal) for 30 days while consuming the Dietary Approaches to Stop Hypertension (DASH) diet (rich in fruits, vegetables, and low-fat dairy) or a more typical American diet. Within each diet and subgroup, there was a general pattern such that the lower the sodium level, the greater the mean reduction in BP. Sodium reduction from 100 to 50 mmol/2,100 kcal generally had twice the effect on BP as reduction from 150 to 100 mmol/2,100 kcal.

The influence of age on the effect of sodium reduction was particularly strong in nonhypertensive patients: -3.7 mm Hg systolic for <45 years and -7.0 mm Hg for >45 years with the typical diet and -0.7 and -2.8 mm Hg with the DASH diet. Reduced sodium intake and the DASH diet should be advocated for the prevention and treatment of high BP, particularly because the benefits to BP strengthen as subjects enter middle age, when the rate of cardiovascular disease increases sharply.

[John Bentley]

Originally posted by materia3
Some us seem to be talking ourselves out of low salt intake to lower blood pressure particularly if we are hypertensive although recent findings are bringing back the older notions that sodium restriction can help prevent HTN as well. Over the past two or three years there has been some impressive research under the acronym DASH (Dietary Approaches to Stop Hypertension) which can be accessed in MedLine and elsewhere that may be worth a look.

Here's part of one recent abstract:

I am NOT showing this to my wife. Darn it!

[Jon_in_london]

Anecdote alert....

I sometimes get high blood pressure, probably due to afore mentioned problems with kidneys not excreteing Na blaghb blahh blagh....

Anyway, I can actually feel the effects of eating too much salt. Its quite remarkable. My BP goes through the roof if I eat a McD's, my pulse rate increases and I feel light headed.

This is why I stay well away from salty foods and never do nasty burgers. I have actually cut out all table salt, which is quite remarkable because I litteraly used to use a tablespoon of salt per plate of food.