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I'm a medical student who actually read the paper this article refers to. I would be very careful trying to draw conclusions from a study like this. I don't thi

by svsaraf 12y ago

I'm a medical student who actually read the paper this article refers to. I would be very careful trying to draw conclusions from a study like this. I don't think many people in the healthcare community would be very surprised by it. 1) All clinically treated hypertensive patients were excluded - that means if you have kidney or vascular disease (hypertension) and are being treated for it, you aren't counted here. Doctors WILL care about your salt intake if you have these conditions, as they should! It is very common to prescribe something called the DASH diet to lower sodium intake and increase potassium intake. 2) If you're healthy, it means your kidneys are healthy (simplifying). One of the purposes of the kidneys is to maintain homeostatic blood pressure by excreting a combination of salt and water. To put it simply, if you eat a huge load of NaCl, say in a dominoes pizza, your blood pressure WILL NOT be affected for a very long time. I'd guess 20 minutes or so after the salt enters your bloodstream. Which means these folks can't measure that blood pressure change by testing blood pressure yearly. 3) Either medical doctors or the press that listens to them have a nasty habit of taking treatments that often work for very sick people - morbidly obese, type 1 diabetics, bed-ridden centenarians - and applying it to normal healthy folks. I will go out on a limb and say that these unilateral recommendations are almost all BS, and should be ignored. If you're healthy: eating eggs will not affect your cholesterol, eating cheesecake will not give you diabetes, sitting in a chair will not misalign your spine. It would be prudent for you to be skeptical when you hear these claims, often on daytime television or on the internet.

graeme 12y ago
Number 3 is very interesting. I understand why the press would make silly claims. But why would medical doctors apply those claims to normal people? Assuming they're not generally considered valid for those who are healthy.
- DanBC 12y ago
  Medical doctors are just people and are subject to the same biases as everyone else.
Pxtl 12y ago
For #3 the reverse is also true. If Omega 3s do anything to prevent heart disease, it's too late to help if you start gobbling fish-oil once you've got heart disease - study demonstrated no improvement in outcomes for that.
pbhjpbhj 12y ago
>your blood pressure WILL NOT be affected for a very long time // I was confused but I think you mean "your blood pressure will only be affected for a short time". You can parse what you said that way but your expression more readily reads [to me, an en-gb native] as saying that blood pressure changes will only appear a long time after salt intake. I've read that salt has an almost immediate effect on blood pressure and so is used in some emergency treatments to increase blood pressure rapidly. I'd no idea of the mechanism of it though so the hint in 2) is welcome, thanks.
- svsaraf 12y ago
  Thanks for the clarification - that's what I meant. I'm not sure I can edit the parent post. Salt does have an immediate effect on blood pressure, as you said, because of osmotic effects. Increased salt in the intravascular space will draw water from other areas into the vessels, thus increasing blood pressure. The kidney has both osmotic and pressure sensitivity.
  - zvrba 12y ago
    > Salt does have an immediate effect on blood pressure, as you said, because of osmotic effects. Oh, that's also how it kills slugs! (Irrelevant remark; I've just put together two contexts containing "osmotic pressure").
Lost_BiomedE 12y ago
Yep. For many years, I have thought the data has been pointing to potassium deficiency in normal folks. With kidney issues, just as you said. Even with a very healthy diet, the large majority miss the RDA in potassium. Good to see the medical professionals slowly turn towards this conclusion (slowly is likely good, BTW).
dreamfactory2 12y ago
I have read that only a percentage of the population are sensitive to salt and that has been extrapolated to the whole population because a) it's quite hard/expensive to test, and b) you can theoretically still achieve reductions in average disease and mortality by limiting everybody's intake. If that's true it's somewhat like making everybody wear glasses, whilst understating the risks to the folks who are actually sensitive.
- JoeAltmaier 12y ago
  But its simple to measure! Take your blood pressure; eat a lot of salty stuff; take your blood pressure. This is how I learned that caffeine raises my blood pressure about 20 pts. One can of coke. Sigh. And every doctor I have says "oh that's not true, you'd have to drink like 35 cups of coffee". And I'd like to tell them "The more you talk, the less I respect your opinion". Off topic, but what is it about experts that make them spout off their book knowledge exactly when they're faced with contradicting evidence?
  - illumen 12y ago
    It's well known that caffeine causes a rise in blood pressure. That's one reason we have 300-400mg daily maximum level limit. I find this quite disturbing that your doctors didn't know this. There's a lot of sugar in there too, which is also linked to high blood pressure.
  - embolalia 12y ago
    The issue is that plenty of people come in spouting complete nonsense that they "know" about their health, and they're usually wrong. It creates a default reaction. Imagine someone coming in and saying they can't send emails more than 500 miles. If you'd never heard [that story][1] before, you'd probably think they were being ridiculous. They may be absolutely right, but it sounds so different from what you know that you default to saying "Email really doesn't work that way, generally." It doesn't help that you're used to people coming in and saying that a virus put porn in their browser history. [1]: http://www.ibiblio.org/harris/500milemail.html http://www.ibiblio.org/harris/500milemail.html
  - 12y ago
zekenie 12y ago
Hey doc-to-be: Am I correct that there is a very basic cellular bio reason that salt causes vasoconstriction? No one is questioning this?
- ghkbrew 12y ago
  Salt doesn't cause vasoconstriction (constriction of blood vessels). That's not really in dispute. It's whether increased salt intake leads to increase blood pressure. The theory behind this is that increases salt in the vascular spaces will draw in more fluid volume through osmotic pressure, which results in higher blood pressure. The problem is there's a lot more going on in the body than basic hydrostatic forces and in general the body is pretty good at maintaining homeostasis in the face of external perturbation. As one, very relevant example, the kidneys are constantly excreting both salt and fluid in opposition to various changes in blood pressure and chemistry. We know there are patients who are sensitive to salt in their diets. Particularly those with decreased kidney function. This and some other studies are asking the question whether increased salt intake in otherwise healthy individuals leads to an increase in blood pressure. So far the answer seems to be a resounding ...maybe.
sergiosgc 12y ago
1) In trying to find out if, generically, there is a causal effect between salt intake and blood pressure, it is sensible to select a healthy population. The hypothesis being tested is "In good working condition, the human body maintains correct NaCl levels". You do not want to test people with faulty metabolism, because they are outside the scope. 2) See explanation in number 1. 3) I have not read the original paper, but the news article makes no mention of such inference. I have to say that I think the premise that the human body must be excellent at maintaining NaCl levels perfect is sound. Sodium and chlorine are very active chemical elements. Having them in wrong levels probably throws every chemical reaction in the body out of whack. If I were to design a chemical machine that used NaCl, keeping the correct level would be a primary control. Evolution tends to get these things right, so our bodies probably do have excellent control mechanisms for this balance.
- vanderZwan 12y ago
  > In trying to find out if, generically, there is a causal effect between salt intake and blood pressure, it is sensible to select a healthy population. That only holds if the causal relationship does not affect health in any other way. > The hypothesis being tested is "In good working condition, the human body maintains correct NaCl levels". Maybe I'm misinterpreting things, but isn't maintaining correct NaCl levels is by definition part of a good working condition? Sounds a bit circular.
  - sergiosgc 12y ago
    > Maybe I'm misinterpreting things, but isn't maintaining correct NaCl levels is by definition part of a good working condition? Sounds a bit circular. You're misinterpreting the definition of "good working condition". Good working condition, as I meant it means that it is operating as "designed" (no religious meaning intended), i.e. no malfunctions in any part are identified. It could be perfectly possible that, in good operating condition, the error margin on the NaCl control system allows for NaCl levels that cause hypertension. The hypothesis negates this possibility, and the hypothesis test seems to prove that the error margin on the body's NaCl level control keeps it narrow enough to exclude salt intake as a cause of hypertension (on healthy adults, of course).
pothibo 12y ago
Oxford journal isn't your daytime television show. For a med STUDENT you show quite a lot arrogance. You also misunderstand how studies works (All clinically treated hypertensive patients were excluded for a reason. Guess which?) Can't believe you were upvoted since most of what you wrote is just self-serving and has absolutely no links with the study. (I read the original study too)
- svsaraf 12y ago
  Believe it or not, I'm not criticizing the study. It certainly has weaknesses, but I agree with its conclusion and its general methodology. I'm criticizing Time magazine for making the claim that salt has no effect on blood pressure (or implying it), which is demonstrably not true. My point is: if you're healthy, no, it isn't surprising that your body can regulate salt intake. If you aren't, it isn't surprising that doctors will want to keep track of how much salt you're eating. > For a med STUDENT you show quite a lot arrogance. I wish you hadn't said this, because I think it's unnecessary and diminishes the rest of your comment.
free2rhyme214 12y ago
I agree with you. I trust Paul Bragg more than a biased health study.

by svsaraf 12y ago

graeme 12y ago

Number 3 is very interesting. I understand why the press would make silly claims. But why would medical doctors apply those claims to normal people? Assuming they're not generally considered valid for those who are healthy.

DanBC 12y ago
Medical doctors are just people and are subject to the same biases as everyone else.

Pxtl 12y ago

For #3 the reverse is also true. If Omega 3s do anything to prevent heart disease, it's too late to help if you start gobbling fish-oil once you've got heart disease - study demonstrated no improvement in outcomes for that.

pbhjpbhj 12y ago

>your blood pressure WILL NOT be affected for a very long time // I was confused but I think you mean "your blood pressure will only be affected for a short time". You can parse what you said that way but your expression more readily reads [to me, an en-gb native] as saying that blood pressure changes will only appear a long time after salt intake. I've read that salt has an almost immediate effect on blood pressure and so is used in some emergency treatments to increase blood pressure rapidly. I'd no idea of the mechanism of it though so the hint in 2) is welcome, thanks.

svsaraf 12y ago
Thanks for the clarification - that's what I meant. I'm not sure I can edit the parent post. Salt does have an immediate effect on blood pressure, as you said, because of osmotic effects. Increased salt in the intravascular space will draw water from other areas into the vessels, thus increasing blood pressure. The kidney has both osmotic and pressure sensitivity.
- zvrba 12y ago
  > Salt does have an immediate effect on blood pressure, as you said, because of osmotic effects. Oh, that's also how it kills slugs! (Irrelevant remark; I've just put together two contexts containing "osmotic pressure").

Lost_BiomedE 12y ago

Yep. For many years, I have thought the data has been pointing to potassium deficiency in normal folks. With kidney issues, just as you said. Even with a very healthy diet, the large majority miss the RDA in potassium. Good to see the medical professionals slowly turn towards this conclusion (slowly is likely good, BTW).

dreamfactory2 12y ago

I have read that only a percentage of the population are sensitive to salt and that has been extrapolated to the whole population because a) it's quite hard/expensive to test, and b) you can theoretically still achieve reductions in average disease and mortality by limiting everybody's intake. If that's true it's somewhat like making everybody wear glasses, whilst understating the risks to the folks who are actually sensitive.

JoeAltmaier 12y ago
But its simple to measure! Take your blood pressure; eat a lot of salty stuff; take your blood pressure. This is how I learned that caffeine raises my blood pressure about 20 pts. One can of coke. Sigh. And every doctor I have says "oh that's not true, you'd have to drink like 35 cups of coffee". And I'd like to tell them "The more you talk, the less I respect your opinion". Off topic, but what is it about experts that make them spout off their book knowledge exactly when they're faced with contradicting evidence?
- illumen 12y ago
  It's well known that caffeine causes a rise in blood pressure. That's one reason we have 300-400mg daily maximum level limit. I find this quite disturbing that your doctors didn't know this. There's a lot of sugar in there too, which is also linked to high blood pressure.
- embolalia 12y ago
  The issue is that plenty of people come in spouting complete nonsense that they "know" about their health, and they're usually wrong. It creates a default reaction. Imagine someone coming in and saying they can't send emails more than 500 miles. If you'd never heard [that story][1] before, you'd probably think they were being ridiculous. They may be absolutely right, but it sounds so different from what you know that you default to saying "Email really doesn't work that way, generally." It doesn't help that you're used to people coming in and saying that a virus put porn in their browser history. [1]: http://www.ibiblio.org/harris/500milemail.html http://www.ibiblio.org/harris/500milemail.html
- 12y ago

zekenie 12y ago

Hey doc-to-be: Am I correct that there is a very basic cellular bio reason that salt causes vasoconstriction? No one is questioning this?

ghkbrew 12y ago
Salt doesn't cause vasoconstriction (constriction of blood vessels). That's not really in dispute. It's whether increased salt intake leads to increase blood pressure. The theory behind this is that increases salt in the vascular spaces will draw in more fluid volume through osmotic pressure, which results in higher blood pressure. The problem is there's a lot more going on in the body than basic hydrostatic forces and in general the body is pretty good at maintaining homeostasis in the face of external perturbation. As one, very relevant example, the kidneys are constantly excreting both salt and fluid in opposition to various changes in blood pressure and chemistry. We know there are patients who are sensitive to salt in their diets. Particularly those with decreased kidney function. This and some other studies are asking the question whether increased salt intake in otherwise healthy individuals leads to an increase in blood pressure. So far the answer seems to be a resounding ...maybe.

sergiosgc 12y ago

1) In trying to find out if, generically, there is a causal effect between salt intake and blood pressure, it is sensible to select a healthy population. The hypothesis being tested is "In good working condition, the human body maintains correct NaCl levels". You do not want to test people with faulty metabolism, because they are outside the scope. 2) See explanation in number 1. 3) I have not read the original paper, but the news article makes no mention of such inference. I have to say that I think the premise that the human body must be excellent at maintaining NaCl levels perfect is sound. Sodium and chlorine are very active chemical elements. Having them in wrong levels probably throws every chemical reaction in the body out of whack. If I were to design a chemical machine that used NaCl, keeping the correct level would be a primary control. Evolution tends to get these things right, so our bodies probably do have excellent control mechanisms for this balance.

vanderZwan 12y ago
> In trying to find out if, generically, there is a causal effect between salt intake and blood pressure, it is sensible to select a healthy population. That only holds if the causal relationship does not affect health in any other way. > The hypothesis being tested is "In good working condition, the human body maintains correct NaCl levels". Maybe I'm misinterpreting things, but isn't maintaining correct NaCl levels is by definition part of a good working condition? Sounds a bit circular.
- sergiosgc 12y ago
  > Maybe I'm misinterpreting things, but isn't maintaining correct NaCl levels is by definition part of a good working condition? Sounds a bit circular. You're misinterpreting the definition of "good working condition". Good working condition, as I meant it means that it is operating as "designed" (no religious meaning intended), i.e. no malfunctions in any part are identified. It could be perfectly possible that, in good operating condition, the error margin on the NaCl control system allows for NaCl levels that cause hypertension. The hypothesis negates this possibility, and the hypothesis test seems to prove that the error margin on the body's NaCl level control keeps it narrow enough to exclude salt intake as a cause of hypertension (on healthy adults, of course).

pothibo 12y ago

Oxford journal isn't your daytime television show. For a med STUDENT you show quite a lot arrogance. You also misunderstand how studies works (All clinically treated hypertensive patients were excluded for a reason. Guess which?) Can't believe you were upvoted since most of what you wrote is just self-serving and has absolutely no links with the study. (I read the original study too)

svsaraf 12y ago
Believe it or not, I'm not criticizing the study. It certainly has weaknesses, but I agree with its conclusion and its general methodology. I'm criticizing Time magazine for making the claim that salt has no effect on blood pressure (or implying it), which is demonstrably not true. My point is: if you're healthy, no, it isn't surprising that your body can regulate salt intake. If you aren't, it isn't surprising that doctors will want to keep track of how much salt you're eating. > For a med STUDENT you show quite a lot arrogance. I wish you hadn't said this, because I think it's unnecessary and diminishes the rest of your comment.

free2rhyme214 12y ago

I agree with you. I trust Paul Bragg more than a biased health study.