# Salt and blood pressure

Discussion in 'Chemistry' started by timojin, Jan 17, 2016.

1. ### timojinValued Senior Member

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Why the table salt content have an effect on blood pressure

3. ### timojinValued Senior Member

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Is the culprit for water retention Sodium or the Chloride ion ?

5. ### exchemistValued Senior Member

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osmotic pressure.

7. ### Edont KnoffRegistered Senior Member

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New studies show that the effects are unclear and diverse. There is a group of people whose blood pressure stays stable even at high intake of salt. For another group, blood pressure raises. And for some people, blood pressure even drops with higher salt intake.

There doesn't seem to be a simple, mechanical explanation. Salt messes with the regulatory systems of some persons, but not all; and the results of the mess aren't even consistent.

I've no good sources, even less English ones, but I can present this article:
http://www.welt.de/gesundheit/article112386580/Vergessen-Sie-den-Mythos-vom-ungesunden-Salz.html

It shows two findings:

- Salt has much less influence on blood pressure than generally believed (less than 1% pressure change in the study)
- The effects of little salt intake can be quite bad as well, so the general sugegstion to reduce salt can be harmful

Sorry for not having better sources, but it's time to abandon the old "much salt gives high blood pressure" rule. It's not that simple.

8. ### exchemistValued Senior Member

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Thanks for this. From what I read, some people's kidneys excrete excess salt effectively, while others' do not. Thus for some an elevated salt concentration persists in the blood. For these people, osmosis then causes the volume of blood plasma to increase, dilating the blood vessels and increasing blood pressure. For those that excrete the salt, this does not happen and their blood pressure stays normal. So it seems the problem medicine faces is to understand what drives the excretion of excess salt and why it can fail in some but not others.

But indeed as you say, the above implies that it is not so much the amount of salt in the diet, it is the way the body handles that salt. Nevertheless, unless you actually know for sure that your own body is good at excreting salt, it seem a wise precaution not to eat too much.

Last edited: Jan 20, 2016
9. ### Edont KnoffRegistered Senior Member

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I agree. Extremes are usually bad. Same for sugar, alcohol and some other ingredients of our food.

In addition, our body has repair mechanisms, so we can tolerate small amounts even of poisonous substances while in overall good shape. But there are limits, bad effects tend to sum up, and we must be careful in many regards, not to overstress the body.

For salt, I've been wondering for a while why the amount of salt is never given in relation to the amount of water a person drinks. Some people drink less than 1 litre per day, others drink 2, 3 or more litres. I assume, but I don't know, that salt is more problemantic for the those who drink only little. The more water one drinks, the easier it is for the body to get rid of excess salt. I feel somewhat puzzled that notes about the water intake are never given in the publications.

10. ### timojinValued Senior Member

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Let me throw this question in Sodium ions retain about 11 molecules of water chloride one molecule potassium retain one molecule of water .
Could be by any chance the word zaltz ( salt ) in the experiment not discriminated and they may have used NaCl interchangeable with KCl ?
To my understanding Na ions stay in the plasma and the K ions in the cell, an excess of Na will have tendency retain water , One of first order medication to reduce pressure is diuretics ,meaning to reduce the water content.

11. ### exchemistValued Senior Member

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Try again in better English, perhaps?

12. ### timojinValued Senior Member

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Na ion holds 11 molecules of water K ion holds one molecule of water , so the hydration is 11 to one
in our system there is a body of fluid called plasma (out side the cell ) there is were Na ion reside and inside the cell K ion reside ( they keep the potential EV if the cell )
Increasing Na ion some of the Na ions will penetrate into the cell , because if that the cell will swell, that is one scenario. The other scenario is as the water content increase due to osmotic pressure other ions will move into were more water is available ( osmosis )
So the first medication step to reduce high blood pressure are diuretics ( make you urinate )
I hope it is more clear.

13. ### rpennerFully WiredStaff Member

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Not true. For weak solutions, the number of hydration water molecules is 5.3 (Na) or 6.0 (K), while for strong solutions the number is 4.5 (Na) or 4.8 (K).
https://www.researchgate.net/public...ion_and_the_Concept_of_Structure_MakerBreaker

14. ### exchemistValued Senior Member

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Thanks, much better. Yes as my previous post indicated, it seems the increase in pressure is due to greater plasma volume, arising from osmotic effects in the body when there is more salt in the bloodstream. The degree of hydration of the Na and K ions does not seem to be a source of relevant difference, as rpenner makes clear. So your second scenario seems to be the right one. But the challenge, really, is to get the kidneys to excrete, not just more water, but the surplus salt that causes the problem. Or at any rate this seems to be where the focus of attention is.

I had a look at the issue you raise of coordination number of the alkali metal ions in aq. solution and there is a lot of material available. As well as rpenner's source, I thought this one was pretty interesting: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3250073/

They seem to be saying Li is often 4-coordinate while Na is either 5 or 6 and K 6 or 7. This is directionally what one might expect, in view of the relative sizes of the respective ions. Both papers comment on the "weak" nature of the hydration shells of the alkali metals. This I imagine will be by comparison with cations with a charge of 2+ or 3+, which would be expected to attract polar water molecules more strongly.

15. ### timojinValued Senior Member

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What ever your data is , it does not agree with conductivity nor with boiling off water. The larger the hydration the slower the ion mobility.

.From boiling out water to evaluate hydration I have done many years ago my value is 11
Cations λ+0 /mS m2mol−1 anions λ-0 /mS m2mol−1
H+ 34.96 OH− 19.91
Li+ 3.869 Cl− 7.634
Na+ 5.011 Br− 7.84
K+ 7.350 I− 7.68
Mg2+ 10.612 SO42− 15.96
Ca2+ 11.900 NO3− 7.14
Ba2+ 12.728 CH3CO2− 4.09

16. ### rpennerFully WiredStaff Member

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FYI, if you don't recognize it, that's a table of molar conductivities at infinite dilution in water at 298.15 K , from Bard and Falkner Electrochemical Methods (1980) or similar reference. The units are millisiemens meters-squared per mole or $\textrm{mS} \cdot \textrm{m}^2 \cdot \textrm{mol}^{-1}$ or equivalently $10^{-3} \, \textrm{m}^2 \cdot \Omega^{-1} \cdot \textrm{mol}^{-1}$ as both S and Ω are SI units.

Ion mobility is the next column over with units of distance times speed per volt.

Estimates of hydration of an ion, are just that, estimates. So it is important to be clear of your definitions and sources. Some published estimates of the hydration number for sodium have ranged from 1 to 71.
http://pubs.acs.org/doi/abs/10.1021/j150643a008
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3250073/ (I agree this is interesting)

Last edited: Jan 21, 2016
exchemist likes this.
17. ### timojinValued Senior Member

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I don't know what are you implying, I am trying to show that potassium is more conductive then sodium , yet sodium have a larger charge per unit volume , and yet Sodium ion is less conductive then potassium , and the reason is that sodium is surrounded by more water then Potassium. At the same time if you distilled water with different ions you are able to see the cloud of water influenced by the Ion.
This is direct lab work and not indirect measurement.

18. ### exchemistValued Senior Member

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Now I am very impressed! How the hell you recognised that, I have no idea.

But I've a feeling this thread is starting to go downhill, like the cloud formation one.....

19. ### timojinValued Senior Member

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Estimates are estimates on a piece of paper but an experiment is worth more then the estimate