Here is something that catches out even doctors sometimes. A patient has stubbornly low potassium. They are given potassium supplements. The levels barely budge. The missing piece is often magnesium.
Magnesium and potassium are linked at a cellular level in a way that has real consequences. If you are low in both, correcting potassium alone can be like topping up a bucket with a hole in it.
This article explains how the two minerals work together, why a magnesium shortfall can keep potassium low, and what it means if you are trying to get either back on track.
Table of Contents
Two minerals, one team
Magnesium and potassium are both electrolytes, minerals that carry an electrical charge and help run the body’s signalling systems. They are central to nerve impulses, muscle contraction and a steady heartbeat.
Potassium does much of its work inside your cells, where it sits in far higher concentrations than in the blood. Keeping it there is an active job, and that job depends on magnesium.
So while they are different minerals with different roles, they are operationally joined. One props up the other.
How magnesium keeps potassium in place
The link comes down to a tiny gatekeeper in your cell membranes. Potassium tends to leak out of cells through channels, and one important channel is called ROMK.
Magnesium normally blocks part of that channel from the inside, slowing the leak and helping cells hold on to potassium. When magnesium is low, the block weakens, the channel opens up, and potassium escapes more easily. The kidneys then flush that potassium out in the urine.
This is why low magnesium can cause, or sustain, low potassium. The mechanism was set out clearly in a 2007 paper in the Journal of the American Society of Nephrology (Huang and Kuo), which described how magnesium deficiency drives potassium loss and why potassium can be hard to correct until magnesium is restored.
The practical takeaway: if potassium will not come up despite supplementing it, a magnesium shortfall is a prime suspect.
Signs the pair may be low
Because magnesium and potassium overlap so much in what they do, a shortfall in both can produce similar, overlapping signs:
- Muscle cramps, twitches or weakness
- Fatigue and low energy
- Heart palpitations or an irregular heartbeat
- Tingling or numbness
- Low mood or irritability
None of these is specific, and palpitations in particular always warrant a chat with your GP rather than self-diagnosis. They are signals to look closer, not a diagnosis in themselves.
Standard blood tests add a wrinkle here. Blood potassium is measured routinely, but most of your magnesium sits inside cells and bone, so a normal blood magnesium reading can still hide a body-wide shortfall. We unpack that in our guide to the signs of magnesium deficiency.
What drains both minerals
Several everyday factors pull magnesium and potassium down together, which is part of why combined shortfalls are common after 40.
- Diuretics. Many “water tablets” for blood pressure increase the loss of both minerals through urine.
- Stomach upsets. Vomiting and diarrhoea flush out electrolytes quickly.
- Heavy drinking. Alcohol raises urinary loss of magnesium.
- A low-vegetable diet. Fruit, vegetables and pulses are the main dietary source of both minerals, and many people fall short.
- Ageing kidneys. They hold on to less of both over time.
| Drainer | Magnesium | Potassium |
|---|---|---|
| Diuretics (water tablets) | Yes | Yes |
| Vomiting / diarrhoea | Yes | Yes |
| Heavy alcohol use | Yes | Indirect |
| Low-vegetable diet | Yes | Yes |
| Ageing kidneys | Yes | Yes |
Our article on what depletes magnesium covers the medication and lifestyle drivers in more detail.
Getting the balance back
Food first is the right starting point, because whole foods deliver both minerals together along with the fibre and other nutrients that come with them.
Good sources of both magnesium and potassium include:
- Leafy greens such as spinach and chard
- Beans, lentils and other pulses
- Avocado
- Bananas (strong on potassium)
- Pumpkin seeds and almonds (strong on magnesium)
- Potatoes with the skin on
| Food | Stronger in |
|---|---|
| Spinach, chard, leafy greens | Both |
| Beans and lentils | Both |
| Avocado | Both |
| Banana, potato (with skin) | Potassium |
| Pumpkin seeds, almonds | Magnesium |
If your diet falls short, a magnesium supplement can help close the gap, and correcting magnesium is often what allows potassium to recover too. A well-absorbed, gentle form matters here. Magnesium oxide is poorly absorbed, while magnesium glycinate is absorbed well and is kind to digestion.
Our Magnesium Glycinate is a pure, non-buffered bisglycinate that fits an everyday top-up. For the broader role this mineral plays, see our overview of magnesium benefits.
One important caution on potassium. Potassium supplements are not something to take casually, because too much potassium can be as dangerous as too little, especially if your kidneys or heart are not in perfect shape. Get potassium from food, and leave potassium supplementation to your GP. Magnesium is the mineral most people can safely top up themselves, within label doses.
FAQ
Why won’t my potassium go up even with supplements?
A magnesium shortfall is a common reason. Magnesium helps your cells hold on to potassium by blocking a channel that otherwise lets it leak out. When magnesium is low, potassium escapes and is lost in urine, so levels stay low until magnesium is corrected.
Are magnesium and potassium deficiency related?
Yes. Low magnesium can directly cause or sustain low potassium because magnesium controls how much potassium your cells retain. The two also share common causes, such as diuretics, stomach upsets and a low-vegetable diet, so they often run low together.
Should I take magnesium and potassium together?
Magnesium is something most people can safely top up within label doses, and doing so often helps potassium recover. Potassium supplements, by contrast, can be risky and should be left to your GP. Getting potassium from food is the safer route for most people.
What foods are high in both magnesium and potassium?
Leafy greens, beans and lentils, avocado, potatoes with the skin on, and pumpkin seeds all provide both. Bananas are particularly strong on potassium, while seeds and nuts are particularly strong on magnesium.
Can low magnesium cause heart palpitations?
Low magnesium and low potassium are both linked to palpitations and irregular heartbeat, since both minerals help regulate the heart’s electrical activity. Palpitations have many causes, so always have them assessed by your GP rather than assuming a mineral shortfall.
This article is for general information and is not medical advice. Food supplements are not a substitute for a varied, balanced diet and healthy lifestyle. Do not take potassium supplements without medical advice. If you take medication, have kidney or heart concerns, or manage a health condition, speak to your GP or pharmacist before starting a new supplement.
References
- Huang CL, Kuo E. Mechanism of hypokalemia in magnesium deficiency. Journal of the American Society of Nephrology. 2007. link
- Workinger JL, et al. Challenges in the diagnosis of magnesium status. Nutrients. 2018. link
- Whang R, et al. Refractory potassium repletion: a consequence of magnesium deficiency. Archives of Internal Medicine. 1992. link
