Does potassium help lower blood pressure? (A science-based guide)

From the desk of
Robb Wolf
ScienceDoes potassium help lower blood pressure? (A science-based guide)

Most sources agree that eating more potassium may help lower blood pressure. It’s an uncontroversial electrolyte — so much so, that the US government has approved a health claim endorsing potassium-rich foods for reducing blood pressure and stroke risk. The controversy heats up, however, when sodium enters the picture. In the same claim, the government also recommends sodium restriction.

It’s admittedly tough to parse the data on sodium, potassium, and health outcomes — especially when much of it is either observational or derived from dietary intervention trials that don’t (and can’t) control for hundreds of confounding factors.

I mean, if you put someone on a high-potassium diet (one rich in fruits and vegetables) and their blood pressure goes down, what explains that? Is it the potassium, the plant-based antioxidants, the reduction in sodium, a reduced glycemic load (lowering insulin and aldosterone, which causes the body to retain sodium), or is it something else entirely?

The mechanisms get tricky in a hurry, but the “what to do” is, fortunately, fairly straightforward. Eat nutrient-dense whole foods, and avoid nutrient-devoid processed foods.

Now, what should we consider with regard to sodium and potassium intake? To answer, let’s explore the data. This will give us a clearer idea of how potassium and sodium affect blood pressure. Let’s dig in, shall we?

Blood Pressure 101

Your blood pressure is the force of your continuously circulating blood against the walls of your blood vessels. This pressure is largely a function of your beating heart — but it’s also affected by fluid and electrolyte levels, plus how constricted or relaxed our arterial walls are.

Blood pressure is measured by two numbers:

  1. Systolic blood pressure: Blood pressure when your heart beats.
  2. Diastolic blood pressure: Blood pressure between heart beats.

According to the American Heart Association, “normal” blood pressure means having a systolic blood pressure under 120 mm Hg and a diastolic blood pressure under 80 mm Hg. When systolic jumps over 130 (and diastolic over 80), you cross into the realm of high blood pressure (hypertension).

About one-third of Americans suffer from hypertension. It’s a well-established risk factor for both heart disease and stroke. Hypertension is also a risk factor for dementia, as high blood pressure can damage the delicate microvessels in the brain.

Many things can contribute to high blood pressure: poor sleep, obesity, lack of exercise, genetic factors, and — relevant here — potassium deficiency.

What Is Potassium?

Potassium is a mineral that exists in most living tissues. Its chemical symbol is K. Most of the potassium in your body appears as K+. The plus symbol means that it carries a positive charge. There exist many charged minerals (aka electrolytes) which serve your body. The major ones are sodium, chloride, potassium, magnesium, calcium, phosphorus, and bicarbonate.

These minerals come into the human body through diet and go out through sweat, urine, feces, and vomit. Potassium excretion occurs through all of the above routes, though only marginally through sweat.

A large proportion of cellular communication happens through structures called potassium channels. Potassium channels transport K+ to regulate your heartbeat, cellular energy (ATP) production, nervous system communication, and most other functions we care about. You know… LIFE!

Potassium and sodium also help dictate fluid balanceinside and outside your cells. Potassium mostly resides in the fluid inside of your cells, and sodium mostly resides in the fluid outside your cells. Your fluid and electrolyte balance are important for many aspects of physiology. Perhaps the most talked about is blood pressure!

Evidence for Potassium Lowering Blood Pressure

The science on potassium for blood pressure falls into three main buckets:

  1. Observational data
  2. Dietary interventions
  3. Randomized controlled trials

Let’s review these one at a time.

#1: Observational Studies

Across the literature, higher potassium intakes are correlated with lower rates of hypertension.

In one meta-analysis, getting 1.6 more grams of potassium per day through diet was linked to a 21% reduction in stroke risk. (High blood pressure is a primary risk factor for stroke — the interruption of blood supply to the brain.)

But lower blood pressures at higher potassium intakes don’t prove that potassium lowers blood pressure. They merely show a correlation between the two.

#2: Dietary Interventions

Dietary interventions provide slightly higher grade data than observational studies. Unfortunately, it’s impossible to control for many factors (like the beneficial effects of eating more whole foods vs. processed foods) that could be driving the results. But we have to work with the data we have, so let’s look at a couple of examples

Back in the mid 1980s, researchers put folks with hypertension on one of four diets: control, low sodium, high potassium, and low sodium combined with high potassium. What happened? Both of the high potassium groups saw the largest blood pressure reductions — the combined low-sodium and high-potassium group did not see any additional benefit compared to the high potassium group.

A handful of subsequent studies put people on a high-potassium “dietary approaches to stop hypertension” (DASH) diet. The results were mixed, but overall the plant-rich DASH diet did lower blood pressure in hypertensive folks, although it wasn’t clear why. Did DASH work because people were eating less refined garbage? More polyphenols? Less sodium? More potassium?

It’s hard to know for sure. Let’s examine some randomized controlled trials to continue our investigation.

#3: Randomized Controlled Trials

The clinical data on potassium lowering blood pressure is super convincing. Multiple randomized controlled trials (the gold standard of science) show that potassium supplements lower blood pressure over placebo.

Rather than going through these trials individually, let’s look at a recent meta-analysis (a study of studies) that compiles all the literature. The punchline of this 2017 paper was that long-term potassium supplementation (4 weeks or more) led to lower blood pressure in those with hypertension.

Potassium supplements were most effective at lowering blood pressure in:

  • Those with low dietary potassium intakes
  • Salt-sensitive people (more on this soon)
  • People not taking blood-pressure medications

So when you give hypertensive folks potassium supplements, their blood pressure tends to go down. But why?

Why Potassium Lowers Blood Pressure

There are two main explanations why potassium lowers blood pressure. The first is that potassium relaxes the walls of your blood vessels — aka vasodilation. More room for blood to flow means less pressure for a given volume of blood.

The second explanation is that potassium balances the effect of sodium. In a way, sodium and potassium are like yin and yang for blood pressure. Sodium can increase blood volume, thereby increasing blood pressure. Potassium can relax blood vessel walls and increase sodium excretion to decrease blood pressure.

Does this mean that everyone, bar none, should lower sodium intake and raise potassium intake in order to reduce their blood pressure? Not necessarily — let’s investigate sodium more closely now.

Sodium, Potassium, and Blood Pressure

A high-sodium and low-potassium diet is linked to high blood pressure in animals and humans. What’s driving this correlation? If sodium is to blame, then low-sodium diets should cure high blood pressure — but this doesn’t seem to be the case.

In a 2018 paper, researchers split 2,632 people with normal blood pressure into two buckets:

  1. Those consuming under 2.5 grams sodium per day
  2. Those consuming over 2.5 grams sodium per day

If you hypothesize that sodium restriction always reduces blood pressure, you would expect group one to have the lower blood pressure. But in this trial, they interestingly had higher blood pressure than the high sodium group.

Yes, high sodium diets are correlated with high blood pressure, but high sodium diets also tend to be low in potassium and high in sugar. High sugar diets mean excess caloric intake, elevated aldosterone, sodium retention, and (drumroll please…) hypertension. My money is on potassium deficiency and junk food driving the epidemic of hypertension.

What about those genetically prone to hypertension at high salt intakes? Surely these salt-sensitive people should restrict sodium? I’m not so sure. When you give salt-sensitive people extra potassium, their blood pressure comes down nicely. Potassium seems to be the answer here.

I also worry about the dangers of a low-sodium diet: the rapid potassium excretion, the mood-altering effects, and the release of hormones (like aldosterone) that can raise blood pressure. The smart play for blood pressure and general health is to get enough sodium and potassium. Not one or the other.

Getting Enough Potassium for Healthy Blood Pressure

The National Academy of Medicine set the adequate intake (AI) for potassium at 3.4 grams for men and 2.6 grams for women. A mere 20–40% of Americans hit this target. But while adequacy is nice, why not shoot for optimal outcomes? Based on the evidence, I think that most folks would stand to benefit from consuming between 3.5–5 grams of potassium each day.

If you’re consuming a whole foods diet (as opposed to one filled with processed junk), your chance of potassium sufficiency goes up dramatically. Why? Because many whole foods — including meat, fruits, and leafy greens — are full of potassium!

The best way to see if you’re getting enough potassium is to calculate your daily intake with an app like Cronometer. Log your meals to see where you stand, then supplement to make up the shortfall. If you’re feeling ambitious, a neat experiment is to buy a blood pressure cuff and start taking daily readings. See what happens when you bump up your potassium intake.

It’s funny… All of these words, and I can sum up this article quite well by simply saying “prioritize real food.” We don’t need to dive crazy deep on proposed mechanisms, arcane studies, and the latest medical literature experiment to justify that statement. It just makes sense.

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