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The role of potassium in the body
Potassium is the main mineral found inside our cells. This distinguishes it from sodium, its counterpart, which is mainly found outside the cells. Much of the body’s functioning depends on this distribution.
This difference in concentration between the inside and outside of cells creates a difference in electrical charge. It is this charge that enables the transmission of nerve signals and the contraction of muscles, including the heart muscle.
The recognised functions of potassium are directly linked to this mechanism: it contributes to the normal functioning of the nervous system, to normal muscle function and to the maintenance of normal blood pressure.
The nutritional reference value established by ANSES for adults is 3,500 mg per day. This is a high figure compared with other minerals, and a significant proportion of the population does not reach this level, not because of a pathological deficiency, but because their diet is too low in plant-based foods.
Symptoms of potassium deficiency
A distinction must be made between two situations, which have different implications. Inadequate dietary intake is common and generally asymptomatic. Hypokalaemia – that is, an actually reduced blood potassium level – is a medical condition with specific causes and identifiable symptoms.
Cramps and muscle weakness
This is the most common reason for concerns about potassium levels. As this mineral is essential for the contraction and relaxation of muscle fibres, a deficiency results in:
- cramps, particularly in the calves and often at night
- generalised muscle weakness, with a sensation of heavy legs
- fasciculations, those small involuntary twitches beneath the skin
- a prolonged recovery time after exercise in active people
A useful caveat: cramps are rarely caused by potassium alone. Magnesium, calcium, sodium and hydration all play a part, and automatically attributing cramps to a lack of potassium is an oversimplification.
Fatigue and digestive problems
General fatigue, with no obvious cause, often accompanies an established deficiency. This is due to potassium’s role in cellular function throughout the body.
As for the digestive system, the smooth muscles of the gut also rely on potassium to contract. A deficiency can therefore lead to a slowing of bowel movements, constipation and bloating.
These symptoms are non-specific and overlap with those of many other conditions, including iron, vitamin B12 or vitamin D deficiency. This is why a blood test is essential to reach a definitive diagnosis.
Cardiac symptoms
This is the most serious aspect of the issue, and it explains why potassium levels should not be taken lightly. As the heart is a muscle whose rhythm depends on the movement of ions, severe hypokalaemia can cause palpitations, an irregular heart rhythm or premature beats.
Persistent palpitations or an irregular heart rhythm warrant immediate medical attention, regardless of any assumptions about potassium levels.
Causes of a potassium deficiency
A potassium deficiency is almost never caused simply by an inadequate diet. In most cases, it results from increased losses.
Digestive and sweat-related losses
Prolonged vomiting and diarrhoea are the primary causes of potassium loss. A single episode of severe gastroenteritis can be enough to cause blood levels to drop.
Repeated use of laxatives is a common yet underestimated cause, as is significant fluid loss through sweating during prolonged exertion in hot conditions.
Medicines, primarily diuraetics
This is the most common cause of hypokalaemia in clinical practice. Several treatments increase the excretion of potassium by the kidneys:
- diuretics, particularly thiazides and loop diuretics,which are widely used to treat high blood pressure and heart failure
- corticosteroids, when used long-term
- certain laxatives and certain antibiotics
If you are taking any of these treatments, monitoring your potassium levels is the responsibility of your doctor, who will normally include this in your routine blood tests. Never adjust your potassium intake on your own initiative in this context.
Insufficient dietary intake
Insufficient dietary intake rarely causes hypokalaemia on its own, but it exacerbates any other underlying cause and explains why many people remain persistently below the reference level of 3,500 mg.
The typical pattern: a diet low in vegetables, fruit and pulses, and high in processed foods. These provide a lot of sodium and little potassium – exactly the opposite of the desirable ratio between these two minerals.
Potassium-rich foods
Good news: potassium is widely found in plant-based foods, and there are numerous, readily available sources. The banana is the most well-known example, but it is far from being the best.
These figures are indicative averages, which may vary depending on origin and preparation. An important practical point: potassium is water-soluble. Boiling in plenty of water causes a significant amount to be lost, as it leaches into the cooking liquid. Opt for steaming, baking or saving the cooking liquid.
The ratio of potassium to sodium is just as important as the absolute quantity. Increasing your intake of plant-based foods whilst reducing your consumption of processed foods improves this ratio in both respects.
Exercise, sweating and potassium
Sweat loss mainly involves sodium, but potassium is also excreted through sweat, albeit in smaller quantities. During prolonged exercise in hot conditions, these cumulative losses become significant.
What matters for a regular exerciser:
- to meet the recommended intake of 3,500 mg through diet, which means making vegetables, pulses and dried fruit a regular part of your diet
- not automatically attributing cramps to potassium: hydration, sodium and magnesium are at least as often to blame
- replenish all minerals rather than just potassium during prolonged exercise
For long-duration exercise, electrolyte formulations in the mineral salts category are designed to replenish this range of losses in a balanced way, rather than targeting a single mineral.
Should you take potassium supplements?
Here, we need to be more straightforward than with other minerals: potassium is not a supplement to be taken indiscriminately.
The reason is simple and relates to the dual nature of the risk. Just as a potassium deficiency affects heart rhythm, so too is an excess of potassium (hyperkalaemia) a serious medical condition that can affect the heart. Unlike most vitamins, where an excess requires months of high intake, potassium levels are tightly regulated and can become unbalanced more quickly.
Situations in which potassium supplements must be strictly avoided without medical advice:
- kidney failure, at any stage, as the kidneys are the organ responsible for eliminating potassium
- treatment with angiotensin-converting enzyme (ACE) inhibitors, sartans or spironolactone, which cause potassium retention
- poorly controlled diabetes
- adrenal insufficiency
It is also for this reason that dietary supplements containing potassium are subject to regulated maximum levels, which are well below the amounts provided by the diet.
The sensible approach is therefore clear: for cases of insufficient intake, diet is the key, and it is more than sufficient, with foods that are plentiful and readily available. For diagnosed hypokalaemia, management is medical, with blood tests to monitor levels. Dietary supplements have no place in either scenario.
For a comprehensive overview of minerals and their interactions, our guide to the best vitamin and mineral supplements puts potassium into the wider picture.
Frequently Asked Questions
What are the symptoms of a potassium deficiency?
The most common signs are muscle cramps, weakness in the legs, general fatigue, constipation and, in severe cases, palpitations or an irregular heartbeat.
These symptoms are non-specific and may indicate other deficiencies. Only a blood test, prescribed by a doctor, can confirm hypokalaemia. However, persistent palpitations warrant an immediate consultation.
Which food is richest in potassium?
Unsweetened cocoa powder is the food with the highest concentration, containing 1,500 to 2,000 mg per 100 g, but we only consume a few grams at a time.
In practice, the best sources are pulses (white beans, lentils), dried fruit (dried apricots), nuts (almonds, pistachios) and green vegetables. Bananas, with around 360 mg, fall well short of their reputation: an avocado or a portion of spinach provides more.
Can potassium be taken as a dietary supplement?
Not without medical advice. Potassium is one of the few minerals where an excess poses a risk comparable to that of a deficiency, with a possible impact on heart rhythm.
It is strongly advised against in cases of kidney failure or when taking angiotensin-converting enzyme (ACE) inhibitors, sartans or spironolactone. For those with insufficient intake, diet is the appropriate and entirely sufficient solution.
Does potassium lower blood pressure?
Potassium helps maintain normal blood pressure, and this is a recognised claim. The mechanism involves, in particular, its effect on sodium excretion.
Be careful not to jump to conclusions: this does not mean that potassium is a treatment for high blood pressure. If you are being treated for high blood pressure, several of the relevant medicines interact directly with potassium; speak to your doctor before making any changes to your intake.
Potassium or magnesium deficiency: how can you tell the difference?
You cannot tell them apart based on symptoms alone. Cramps, muscle weakness and tiredness are common to both, making self-diagnosis impossible.
An interesting point: these two deficiencies are often linked. A magnesium deficiency actually promotes the loss of potassium via the kidneys, and correcting the potassium level without also correcting the magnesium level will therefore only provide an incomplete result. This is one of the reasons why a blood test, which measures both, is more useful than relying on assumptions.
Potassium is a mineral that people often do not get enough of, but supplementation should not be undertaken without proper guidance. The best approach is through diet: pulses, green vegetables, dried fruit and nuts, cooked in a way that preserves their nutrient content. To compensate for mineral losses during exercise, explore the balanced formulations in the Tsunami Nutrition mineral salts range.
