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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 hy

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).
smeyer 12y ago
>Sodium and chlorine are very active chemical elements How active are the sodium and chlorine ions, which I assume is what you actually get since the salt is dissolved. Do they still have a major effect on most of the chemical reactions in the body? It's not like anyone is ingesting sodium metal. Disclaimer: I have a physics degree but haven't taken chemistry or biology past high school, so I'm very ignorant here.
- grhino 12y ago
  Admittedly not a biochemist, but I believe sodium and chlorine lose most of their activity when they give up or accept that electron, respectively, to fill their octet. From a biochemistry perspective, they are mostly used as convenient ions to generate voltage differences or activate structural changes in enzymes.The chemical difference between sodium ions and potassium ions are relevant at times, free sodium ions or chloride ions are not nearly as reactive as their neutral complements. It's also very unlikely that sodium ions or chloride ions would spontaneously transform into their neutral complements.
svsaraf 12y ago
I almost completely agree with this comment. I should have been more clear - my gripe is not so much with the study but with its interpretation by Time. The study may have its own problems, but draws a conclusion I agree with, that the relationship between salt and blood pressure in healthy people may be overstated. As for your point 3: I disagree. I think the news article makes a case that salt and blood pressure have no relationship, which isn't true. It is only true if, almost by definition, your salt / water regulation system is healthy. Your point about maintaining NaCl levels is probably roughly correct, though I don't think it has been demonstrated per se.
- sergiosgc 12y ago
  > As for your point 3: I disagree. I think the news article makes a case that salt and blood pressure have no relationship, which isn't true. It is only true if, almost by definition, your salt / water regulation system is healthy. It never states the inference directly, although as is common in mainstream media, the title of the piece is stronger than what is then told in the text. I think you may be getting too hung up on the title, and I understand the reason. Mainstream media often over-generalizes scientific findings, more so in the field of nutrition. In the same vein you have a pet peeve with media behaviour, I have one with M.D. behaviour. One that may paint the overly generalized title in a kinder light: Doctors often prescribe life-style changes: Eat less, eat better, exercise more, don't smoke, sleep well, sleep regularly, avoid stress. They fail at prioritizing, because they fail at recognizing that patients will never completely change their lifestyle. Willpower is a limited resource, and should be allocated as such. The prioritization of lifestyle changes is important. If reducing salt intake is competing with reducing BMI, it should be a no-brainer that BMI reduction should come first. It is rarely the case. They are either presented as equally important changes or, since reducing salt intake is easier than shedding 20kg, doctors go for the easy goal. The prioritization problem should be obvious. The closer to the root of problems you attack, the better the result you'll get. Salt intake is way way down the causal chain to health problems. As such, blanket stating that you shouldn't care about salt in your diet may be good, if it leads to freeing willpower to do other lifestyle changes.

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).

smeyer 12y ago

>Sodium and chlorine are very active chemical elements How active are the sodium and chlorine ions, which I assume is what you actually get since the salt is dissolved. Do they still have a major effect on most of the chemical reactions in the body? It's not like anyone is ingesting sodium metal. Disclaimer: I have a physics degree but haven't taken chemistry or biology past high school, so I'm very ignorant here.

grhino 12y ago
Admittedly not a biochemist, but I believe sodium and chlorine lose most of their activity when they give up or accept that electron, respectively, to fill their octet. From a biochemistry perspective, they are mostly used as convenient ions to generate voltage differences or activate structural changes in enzymes.The chemical difference between sodium ions and potassium ions are relevant at times, free sodium ions or chloride ions are not nearly as reactive as their neutral complements. It's also very unlikely that sodium ions or chloride ions would spontaneously transform into their neutral complements.

svsaraf 12y ago

I almost completely agree with this comment. I should have been more clear - my gripe is not so much with the study but with its interpretation by Time. The study may have its own problems, but draws a conclusion I agree with, that the relationship between salt and blood pressure in healthy people may be overstated. As for your point 3: I disagree. I think the news article makes a case that salt and blood pressure have no relationship, which isn't true. It is only true if, almost by definition, your salt / water regulation system is healthy. Your point about maintaining NaCl levels is probably roughly correct, though I don't think it has been demonstrated per se.

sergiosgc 12y ago
> As for your point 3: I disagree. I think the news article makes a case that salt and blood pressure have no relationship, which isn't true. It is only true if, almost by definition, your salt / water regulation system is healthy. It never states the inference directly, although as is common in mainstream media, the title of the piece is stronger than what is then told in the text. I think you may be getting too hung up on the title, and I understand the reason. Mainstream media often over-generalizes scientific findings, more so in the field of nutrition. In the same vein you have a pet peeve with media behaviour, I have one with M.D. behaviour. One that may paint the overly generalized title in a kinder light: Doctors often prescribe life-style changes: Eat less, eat better, exercise more, don't smoke, sleep well, sleep regularly, avoid stress. They fail at prioritizing, because they fail at recognizing that patients will never completely change their lifestyle. Willpower is a limited resource, and should be allocated as such. The prioritization of lifestyle changes is important. If reducing salt intake is competing with reducing BMI, it should be a no-brainer that BMI reduction should come first. It is rarely the case. They are either presented as equally important changes or, since reducing salt intake is easier than shedding 20kg, doctors go for the easy goal. The prioritization problem should be obvious. The closer to the root of problems you attack, the better the result you'll get. Salt intake is way way down the causal chain to health problems. As such, blanket stating that you shouldn't care about salt in your diet may be good, if it leads to freeing willpower to do other lifestyle changes.