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.

It’s so uncontroversial 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 health claim—the one recommending potassium-rich foods—the government also recommends sodium restriction.

Now I’ll be honest. It’s tough to parse the data on sodium, potassium, and blood pressure—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—a diet 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 something different?

The mechanisms get tricky in a hurry, but the “what to do” is, fortunately, fairly straightforward: eat whole, minimally processed foods. Now, what should we consider with regard to sodium and potassium intake?

To answer, we need to look at the whole body of data, not just one or two papers. This will give us a clearer idea of how potassium and sodium affect blood pressure.

Let’s dig in, shall we?

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 tiny “+” means that it carries a positive charge.) The charge allows potassium to conduct electricity and facilitate cellular communication.

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

Charged minerals like K+ have a name: electrolytes. Along with potassium, the other major electrolytes are sodium, chloride, 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.

Potassium and sodium help dictate fluid balance inside and outside your cells. Potassium mostly balances fluid inside your cells, and sodium mostly outside.

Your fluid balance determines your blood pressure, among other things. As blood volume rises, so does blood pressure. This is driven in large part due to relative levels of insulin and aldosterone, which I mentioned earlier.

In a way, sodium and potassium are like yin and yang for blood pressure. Sodium increases blood volume and blood pressure, while potassium relaxes blood vessel walls and increases sodium excretion to decrease blood pressure.

Does this mean you should lower sodium intake as you raise potassium intake? Interestingly, no… or, at least not necessarily. Actually, that could potentially drive the undesirable effect of raising blood pressure. I’ll return to this point later.

Let’s talk more about blood pressure now.

Blood Pressure 101

Your blood pressure is the pressure of your circulating blood against your blood vessel walls. This pressure is largely a function of your pumping heart, but it’s also affected by fluid and electrolyte levels and 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 bp under 120 and a diastolic bp under 80. When systolic jumps over 130 (and the diastolic over 80), you cross into the realm of high blood pressure, also called 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.

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 data

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 potassium lowers blood pressure. They merely suggest it. Also, how does one “naturally” obtain a higher potassium diet? Avoiding those highly-processed foods.

#2: Dietary Interventions

Dietary interventions provide slightly higher grade data than the first bucket. Unfortunately, it’s impossible to control for many factors (like the beneficial effects of eating more whole foods) that could be driving the results. But let’s look at a couple examples anyway.

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? The high potassium groups saw the largest blood pressure reductions. Did the combined low-sodium high-potassium group see a special benefit? It didn’t.

A handful of subsequent studies put people on a high-potassium DASH diet (DASH = dietary approaches to stop hypertension) with mixed results. Overall the plant-rich DASH diet did lower blood pressure in hypertensive folks, but it wasn’t clear why.

Did DASH work because people were eating less refined garbage? More polyphenols? Less sodium? More potassium?

Hard to say. That’s why I prefer the controlled data.

#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. (This is called vasodilation). More room for blood to flow means less pressure for a given volume of blood. As an aside, this is likely why meditation also works against hypertension (as well as many other conditions).

The other explanation is that potassium balances the effect of sodium. Sodium raises blood volume (a component of blood pressure), and potassium mitigates this effect by increasing sodium excretion through urine.

But while this is physiologically true, most people are confused on this topic. In their confusion, they call—not just for more potassium (which the evidence supports)—but also for sodium restriction. Allow me to try to clear up the confusion.

Sodium, Potassium, and Blood Pressure

A high-sodium 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 they don’t.

For instance, the 1988 Intersalt study analyzed over 10,000 people across the globe and found no strong link between salt intake and blood pressure in most populations.

Other research corroborates this finding. 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

Based on the sodium-hypertension hypothesis, you would expect group one to have lower blood pressure. Quite the opposite. They had higher blood pressure than the high sodium group!

It’s not the sodium folks. 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, hypertension, elevated aldosterone, sodium retention and—drumroll—did I mention hypertension?

My money is on potassium deficiency and junk food driving the epidemic of hypertension. It’s not the sodium.

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—enough to hit 3.5–5 grams per day—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 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 government-recommended adequate intake (AI) for potassium is 3.4 grams for men and 2.7 grams for women. This is recently down from an AI of 4.7 grams that, to my eye, had more evidence behind it for healthy blood pressure.

I continue to recommend folks with healthy kidneys shoot for between 3.5 and 5 grams potassium per day. A small percentage of Americans hit this target, but if you’re consuming a whole foods diet, your chance of potassium sufficiency goes up dramatically. Said another way: if one is not eating processed junk, you are likely “good” on potassium.

Why? Because whole foods diets are full of potassium-rich foods like meat, fruits, and vegetables.

To see where you’re at, calculate your daily intake with an app like Cronometer, then supplement to make up the shortfall. (Fun fact: Every stick of LMNT contains 200 mg potassium to help folks do just that.)

If you’re feeling ambitious, get a blood pressure cuff and start taking daily readings. See what happens when you bump up potassium.

But you needn’t experiment on yourself to justify getting enough potassium. Just do it. Your heart will thank you.

To put it plainly: We can dive crazy deep on proposed mechanisms, arcane studies, and the latest medical literature, and I could still sum it up with “just eat real food.”

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