Key Topics Covered

Sodium in a pile on a table

Today we will be exploring the question of: “How much does sodium affect blood pressure?” The title of this podcast leads with the assumption that salt/sodium DOES affect blood pressure. That by itself is a complex topic. We will start by unpacking that first, and then get into more specifics after. 

Cases Against Reducing Sodium Intake

  • I’ve seen a lot of people, particularly in the exercise space, say that trying to reduce sodium intake is a bad idea.
  • The main 3 explanations I’ve seen are:
  1. If you do not have high blood pressure and you are fit and healthy, you probably do not need to worry about reducing sodium. If you are an athlete, you might even benefit from increasing sodium.
  2. There is a thing called sodium sensitivity, or sodium-mediated hypertension. Mainly those who are sensitive to the effect of sodium on hypertension need to worry about sodium intake.
  3. There is a J-Shape curve. Going too high sodium causes issues and going too low sodium causes issues.
  • Addressing that first claim: It’s mostly valid. 
  • Sodium plays a role in blood pressure as we will discuss later. 
  • But if somebody has no issues with their blood pressure, it’s probably not a concern. 
  • If somebody is an athlete who happens to have a very low sodium diet, they might benefit from increasing it. 
  • I will rarely be working with a healthy, active individual and want them to reduce sodium intake, more often, it is the opposite 
  • For example: using salt tablets pre-exercise to avoid lightheadedness 
athlete drinking electrolytes

  • Sodium-mediated hypertension is a thing too. But based on the stats, the vast majority of people who have high blood pressure also fall into the category of having sodium-mediated hypertension.
  • It’s also logistically challenging to test this since you have to test and re-test a lot, for a long time, to confirm if it is relevant for you. 
  • We’ve added a paper in the show notes for this topic if you happen to be interested. 
  • Low sodium diets also do have evidence of contributing to cardiovascular events. 
  • But the dosages are so low. It needs to be well below 1000mg per day before there appears to be any likelihood of issues for most people.
  • It’s pretty impractical to get below there unless you are actively trying to avoid it to an extreme extent. 

Does Sodium Raise Blood Pressure, on Average?

Blood pressure cuff and reading

  • After that stuff, it now makes sense for us to answer “does sodium raise blood pressure, on average?”
  • The answer is succinct: Yes it does. And it’s not debatable at a population level.
  • A 2019 review covering the majority of the research up to that time concluded that reduced sodium intake not only decreased blood pressure but on average reduced morbidity and mortality from cardiovascular diseases.
  • That’s pretty compelling.
  • There are a bunch of mechanisms that play roles here. The simplest one for me is that sodium draws water into the blood, which would increase pressure. But it also increases arterial stiffness and does a few other things.

How Much?

  • So now that we’ve confirmed that it DOES play a role, how much does it matter?
  • There are some nice clear numbers out there.
  • A randomised control trial that involved reducing intake from 3700mg to 2000mg per day found a reduction in systolic blood pressure by ~7.1mmHg (millimetres of mercury) on average.
  • Adding two pieces of context:
  1. Healthy is often considered 120mmHg over 80mmHg. So that adds context as to how much 7.1mmHg is. 
  2. The average sodium intake appears to be 3,500-5,500mg per day. So that RCT is super relevant for the average person. 

Nuance

  • There is a lot of nuance to unpack here.
  • One major one is that sodium is only a small factor in blood pressure. Many other things arguably matter more. These can include things like potassium intake, body weight, activity levels etc.
  • We’ve specifically used numbers – but that’s just because we feel like that is a helpful way to add context. The actual numbers would be very individual from person to person.
  • Another complex thing to factor in is that consistency vs inconsistency with sodium intake plays a bigger role than a lot of people talk about.
  • Your hormones, such as aldosterone, are influenced partly by how much sodium your body expects to be coming in, based on your recent intake. If somebody has a low intake of sodium normally and then randomly has a high intake, they will experience more water retention than somebody who normally has a high sodium intake all the time. This likely plays a role in acute changes in blood pressure too – but is a bit complex to try to summarise simply with numbers like we have with the rest of this stuff.

Summary

  • Sodium DOES play a role in blood pressure on average. It’s not the biggest variable, but it does matter.
  • There is individual variation though and that will be the biggest factor in how much this matters on a person to person level.
    •  Some people are so far away from having high blood pressure, due to other variables, that this won’t play a role.
    • While a high sodium intake may be contributing to the problem for other people.

Relevant Blogs / Resources

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