Effect of High Dietary Sodium Intake in Patients With Postural Tachycardia Syndrome, 2021, Garland et al

[Ryan31337]

Abstract
Background
High sodium intake is recommended for the treatment of postural tachycardia syndrome (POTS) to counteract the hypovolemia and elevated plasma norepinephrine that contribute to excessive orthostatic tachycardia, but evidence of its efficacy is not available.

Objectives
This study tested whether a high sodium (HS) diet reduces orthostatic tachycardia (Δ heart rate) and upright heart rate compared with a low sodium (LS) diet in POTS patients, and secondarily its effect on plasma volume (PV) and plasma norepinephrine.

Methods
A total of 14 POTS patients and 13 healthy control subjects (HC), age 23 to 49 years, were enrolled in a crossover study with 6 days of LS (10 mEq sodium/day) or HS (300 mEq sodium/day) diet. Supine and standing heart rate, blood pressure, serum aldosterone, plasma renin activity, blood volume, and plasma norepinephrine and epinephrine were measured.

Results
In POTS, the HS diet reduced upright heart rate and Δ heart rate compared with the LS diet. Total blood volume and PV increased, and standing norepinephrine decreased with the HS compared with the LS diet. However, upright heart rate, Δ heart rate, and upright norepinephrine remained higher in POTS than in HC on the HS diet (median 117 beats/min [interquartile range: 98 to 121 beats/min], 46 beats/min [interquartile range: 32 to 55 beats/min], and 753 pg/ml [interquartile range: 498 to 919 pg/ml] in POTS vs. 85 beats/min [interquartile range: 77 to 95 beats/min], 19 beats/min [interquartile range: 11 to 32 beats/min], and 387 pg/ml [interquartile range: 312 to 433 pg/ml] in HC, respectively), despite no difference in the measured PV.

Conclusions
In POTS patients, high dietary sodium intake compared with low dietary sodium intake increases plasma volume, lowers standing plasma norepinephrine, and decreases Δ heart rate. (Dietary Salt in Postural Tachycardia Syndrome; NCT01547117)

Effect of High Dietary Sodium Intake in Patients With Postural Tachycardia Syndrome - ScienceDirect

 

[Ryan31337]

Good to see further studies offering evidence for long-held assumptions/observations in POTS treatment. High profile journal too.

Haven't been able to find full-text yet but there's an editorial on the paper from Blair Grubb: High Sodium Intake in Patients With Postural Orthostatic Tachycardia Syndrome∗ : A Practice “Worth Its Salt” | Journal of the American College of Cardiology (jacc.org)

 

[Jonathan Edwards]

I have not tried to access the full paper but two things strike me as odd about the abstract.

Firstly, although they say that high salt altered values in POTS patients they give no results for this (and no statement about statistical significance), while they do give results showing that the POTS values are still abnormal. Why not give the main result of your study - maybe because it is not so impressive?

Also it seems that the plasma volumes were the same between POTS and controls when the other measures were different. That strongly suggests that the other measures are not a result of plasma volume being low. So the theory behind using salt does not seem to add up - since it is supposed to work by restoring plasma volume and thereby normalising heart rate and norepinephrine.

 

[Hoopoe]

For me, in some situations with certain symptoms, upping my salt intake is quite effective at reducing symptoms. I had to do this in the last month, presumably due to the warming weather.

The symptoms that it improves are: fast heart rate, feeling stressed, chest pain, dizzy, orthostatic hypotension, feeling generally weak and unwell.

Water alone doesn't have this effect.

 

[Hutan]

although they say that high salt altered values in POTS patients they give no results for this (and no statement about statistical significance), while they do give results showing that the POTS values are still abnormal. Why not give the main result of your study - maybe because it is not so impressive?

Yes, it is odd. From the editorial, mentioned in Ryan31337's post above:

Interestingly, while orthostatic symptoms improved while on the high-sodium diet, the decline did not reach statistical significance. However, this may have been due to difficulties in the measurement tool used.

I'm not sure what is meant by 'orthostatic symptoms', but the abstract doesn't mention any subjective outcomes being measured. The writer of the editorial seems very impressed, calling it a superb study. Maybe it's just the abstract that isn't so informative. It will be interesting to see.

 

[Ravn]

Haven't been able to find full-text yet but there's an editorial on the paper from Blair Grubb: High Sodium Intake in Patients With Postural Orthostatic Tachycardia Syndrome∗ : A Practice “Worth Its Salt” | Journal of the American College of Cardiology (jacc.org)

From the linked article, my bolding:

They convincingly showed that compared with those on a low-sodium diet, subjects on a high-sodium diet demonstrated a smaller increase in heart rate and lower norepinephrine level, PRA, and aldosterone level while upright. Interestingly, blood volume was lower in POTS patients then that of healthy control subjects, even with a high-sodium diet. This finding matches well with previous data that many POTS patients are clinically hypovolemic. Interestingly, while orthostatic symptoms improved while on the high-sodium diet, the decline did not reach statistical significance. However, this may have been due to difficulties in the measurement tool used.

FWIW, salt never made any difference to me. My POTS gets worse during PEM and in warm temperatures and reduces when not in PEM and in colder temperatures, very high salt or low salt. Pity really, would have been an easy fix, and a tasty one, too.

Edit: cross-posted with Hutan.

 

[Hutan]

There's a Medscape article:
https://www.medscape.com/viewarticle/949982#vp_1

Heart rate increased by 46 beats/min with the high-sodium diet, vs 60 beats/min with the low-sodium diet.

Looks like there were subjective symptom reports - it looks as though this is what is being commented on as nonsignificant:

There was a nonsignificant trend for a lower symptom burden score among the POTS patients who received the high-sodium diet in comparisoin with those taking the low-sodium diet. Scores for mental confusion, palpitations, lightheadedness, and headache trending downward on the high-sodium diet.

"We found that high levels of dietary salt did what we hoped, with increased blood volume and reduced norepinephrine levels on standing and reduced excessive increase in heart rate. While it didn't completely normalize heart rate, this was reduced significantly," Raj said.

Another observation from the study was that the increased salt intake seemed to be beneficial across the whole spectrum of patients.

"There are some patients who have very high levels of sympathetic activation, and there have been anecdotal reports that increasing salt may not work so well in this group," he said. "In this study, we didn't differentiate, but average norepinephrine levels were very high, and many patients would be considered to be hyperadrenergic. Our results suggest this treatment will help these patients too."

It's noted that this was a short study, and so it doesn't provide information about risks from long term high salt intake:

Recognizing that there may be concerns about hypertension with long-term use of such a treatment, Raj said there were no signs of an increase in blood pressure in this study. "But this should be considered a short-term therapy for the time being, and patients need to be reassessed every few years as their physiology changes," he said.

 

[Trish]

For me, in some situations with certain symptoms, upping my salt intake is quite effective at reducing symptoms. I had to do this in the last month, presumably due to the warming weather.

The symptoms that it improves are: fast heart rate, feeling stressed, chest pain, dizzy, orthostatic hypotension, feeling generally weak and unwell.

Water alone doesn't have this effect.

We lose salt in sweat, so hot weather, or activities that induce sweating mean everyone needs more salt, and lack of sufficient salt leads to the sort of symptoms you describe. That's true for anyone. The question seems to be whether low salt is a cause of POTS. it seems from those study that it might be part of the problem, but not the whole story.

 

[Hoopoe]

The weather isn't even particulary warm. It seems to be the adaptation process to warmer weather that is difficult and slow. Eventually I get used to even hot weather. Or maybe there is something else going on metabolically or immunologically in response to the warmer spring. A shift towards a warm weather metabolism or pollen in the air perhaps? When the wind blows strongly, clouds of pollen are carried away from the cypress trees in front of my house.

 

[MeSci]

I definitely need more salt, as I have suffered from severe hyponatraemia at least twice - ending up in hospital a couple of times, and needing a saline drip on at least one occasion.

Since I've been having about one and a half to two teaspoons of sodium bicarbonate in water per day, I think I am a bit better.

Not sure if I have postural tachycardia. I think that my pulse is higher when standing, but the drug I take for high blood pressure (Nebivolol) keeps my pulse quite low.

 

[Jonathan Edwards]

Interestingly, blood volume was lower in POTS patients then that of healthy control subjects, even with a high-sodium diet. (From the review)

But that does not seem to be what the abstract says? It says there was no difference, despite the other variables still being different?

 

[Mij]

Sodium triggers your thirst mechanism and helps to reduce fluid losses from the urine- sodium helps to keep you hydrated. Adding sodium in your diet/drinks aids in the hydration process.

This is not POTS related as Trish mentioned.

I can stay upright longer when I drink electrolytes.

 

[Ryan31337]

Interestingly, blood volume was lower in POTS patients then that of healthy control subjects, even with a high-sodium diet. (From the review)

But that does not seem to be what the abstract says? It says there was no difference, despite the other variables still being different?

Could they have measured total blood volume separately to plasma volume? They refer to them as separate variables at the start of the results paragraph.

 

[Jonathan Edwards]

Sodium triggers your thirst mechanism and helps to reduce fluid losses from the urine- sodium helps to keep you hydrated. Adding sodium in your diet/drinks aids in the hydration process.

Are you sure? That is not the physiology I was taught.

As I understand it almost nobody is short of salt in developed countries at least. Historically people were entirely healthy on much lower salt intakes.

 

[Jonathan Edwards]

Could they have measured total blood volume separately to plasma volume? They refer to them as separate variables at the start of the results paragraph.

I cannot see any good reason why plasma and total blood volume should behave differently in this study. They may use the words semi-interchangeably, assuming that measured plasma volume reflects blood volume?

 

[Ryan31337]

It was reported that this article will be free to read for a limited time - perhaps only after the journal publication date in May?

Anyway, the images seem to be there and with a bit of sneaky thumbnail renaming you can see:


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[cassava7]

6 days of LS (10 mEq sodium/day) or HS (300 mEq sodium/day) diet
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For reference, the high sodium diet equates to 17.5g of table salt* per day (7g sodium), or about 3 teaspoons. This is 3.5 times the reference intake of salt for adults per the European Food Safety Authority (most countries recommend 5 to 6g of table salt per day for adults).

Regarding blood volume in this trial, was the participants' daily fluid consumption controlled? One would expect that the high sodium diet made them thirsty and that this led them to increase their usual fluid intake -- they were likely instructed to do so --. However, if the increase in blood volume in the POTS group is not statistically significant, would this suggest that some were not drinking enough?

As a side comparison, this high sodium diet could be replicated by drinking slightly more than 3 liters per day of WHO's formula for oral rehydration solution (ORS), which has been trialed for POTS. It contains 90 mEq or 2.1g sodium per liter. This would require cutting back on other dietary sources of sodium.

* 1 gram of sodium equals 43mEq sodium and table salt, i.e. sodium chloride (NaCl), is about 40% sodium and 60% chloride by weight.

 

[Mij]

As I understand it almost nobody is short of salt in developed countries at least. Historically people were entirely healthy on much lower salt intakes.

It's possible that people with certain medical conditions need to find the right balance between sodium and water intake, this includes electrolytes. Diabetes insipidus for example. I don't know what hormonal imbalances I have, but a higher sodium intake improves my overall being.

 

[Ryan31337]

As a side comparison, this high sodium diet could be replicated by drinking slightly more than 3 liters per day of WHO's formula for oral rehydration solution (ORS), which has been trialed for POTS. It contains 90 mEq or 2.1g sodium per liter. This would require cutting back on other dietary sources of sodium.

Suspect there may be concerns over tolerance - I often see complaints from patients saying the high salt intake creates GI problems. Perhaps the investigators felt it better tolerated with meals.

 

[MeSci]

It's possible that people with certain medical conditions need to find the right balance between sodium and water intake, this includes electrolytes. Diabetes insipidus for example. I don't know what hormonal imbalances I have, but a higher sodium intake improves my overall being.

Whatever it is, it hasn't filtered down to my local hospital. They supposedly tested me for hormonal imbalances. I went in specially for that, and experienced extreme fluid build-up due to having to sit up still for so long, but they weren't interested in that. They also forgot to tell me that the test was over and I could go home!