Supplements
Should you take a potassium supplement? What to check first
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed August 20266 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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Most people get the potassium they need from food, and a supplement is rarely necessary. Potassium is the one mineral where too much is genuinely risky, because your kidneys clear it. If you take a blood pressure medicine, or your kidney function is reduced, ask your GP before you start.
You have read that potassium lowers blood pressure. Maybe you feel better on days you eat more of it. So the next thought is to buy a tub.
Hold on one step. Potassium does not behave like the other minerals on the shelf, and the reason sits in your kidneys.
By the Helvy Medical Team · Reviewed by a qualified clinician · 6 min read
As of August 2026. Includes the systematic review posted to medRxiv on 9 December 2025, which is a preprint and has not yet been peer reviewed.
1. Why potassium is the careful one
Most minerals are forgiving. Take too much magnesium and you get an upset stomach. Potassium is different.
Your kidneys do nearly all the work of clearing potassium from your blood. When they cannot keep up, the level climbs. Doctors call that hyperkalaemia. It can disturb your heart rhythm, and often causes no symptoms until it is well advanced.
That is why the NHS singles potassium out from every other mineral on the shelf:
“Older people should not take potassium supplements unless advised to by a doctor.”
— NHS, Vitamins and minerals: others
The NHS gives the reason in the same breath. Older kidneys, it says, “may be less able to remove potassium from the blood”. Age is a rough proxy for kidney function. Your actual filtering rate is the sharper number, and you can measure it.
Food is a gentler route. Adults aged 19 to 64 need 3,500mg of potassium a day, according to the NHS. Potatoes, beans, pulses, leafy greens and bananas are the usual sources, and they deliver it slowly alongside water and fibre. A concentrated capsule does not.
2. What to check first: how well your kidneys filter
If the risk runs through your kidneys, kidney function is what to know first. Three markers describe it.
- Creatinine is a waste product your muscles make around the clock. Healthy kidneys clear it steadily, so a rising level suggests they are clearing less
- eGFR stands for estimated glomerular filtration rate. It uses your creatinine, age and sex to estimate how fast your kidneys filter blood. Ninety or above is normal
- Urea is a waste product from protein breakdown, also cleared by the kidneys. It moves with hydration, so it is read next to the other two rather than alone
Our Thyroid & Vital Organs panel (£159) measures urea, creatinine and eGFR from a home finger-prick sample, analysed by UKAS-accredited UK laboratories. It reads your cholesterol breakdown in the same draw, which matters if blood pressure is what brought you here.
One honest limit, stated plainly. We do not measure potassium itself. Potassium shifts quickly, so it is best checked by your GP as part of a urea and electrolytes test. A Helvy panel tells you how well your kidneys are filtering, which is what governs your risk. It does not tell you your potassium level.
3. What the new blood pressure research actually found
Interest jumped after a review posted in December 2025. It pooled 19 randomised trials covering 803 adults with untreated high blood pressure. Measured in a clinic, potassium supplements lowered the top number by 7.2 mmHg and the bottom number by 4.0 mmHg.
That sounds like a lot. The same review also pooled readings from monitors worn for a full 24 hours, which are generally the more reliable measure. Those numbers were much quieter: 2.4 mmHg and 1.6 mmHg.
Two details the coverage skips. Side effects were more than twice as common on potassium. And everyone in it had untreated high blood pressure. If you already take a blood pressure medicine, this research did not study you, and you are the one most at risk.
There is a claim you can trust here, and it is narrower than the headlines. “Potassium contributes to the maintenance of normal blood pressure” is authorised on the GB Nutrition and Health Claims Register. That describes what the nutrient does in a normal diet. It is not a promise that a capsule will bring down a reading that is already high.
4. What low potassium feels like
A low blood potassium level is called hypokalaemia. It can cause muscle weakness, cramps, constipation, tiredness and a fluttering or skipping heartbeat. Those are vague symptoms, and plenty of other things cause them.
Low potassium is almost always a symptom of something else rather than a diet gap. Vomiting, diarrhoea and water tablets are the common reasons. Treating the number without finding the cause misses the point.
Magnesium is worth a mention too. When magnesium is low, potassium becomes stubborn and hard to correct, so the two are often looked at together. You can measure magnesium in our General Energy & Wellness panel (£149). Potassium itself still belongs with your GP.
5. Who should not take potassium without asking a doctor
Speak to your GP or pharmacist first if any of these apply to you.
- You take an ACE inhibitor such as ramipril or lisinopril, or an ARB such as candesartan
- You take spironolactone, amiloride or triamterene. The NHS lists these, alongside potassium itself, as medicines that raise the potassium in your blood
- You have reduced kidney function or chronic kidney disease of any stage
- You are older, per the NHS advice quoted above
- You use a low-sodium salt substitute. Most swap some of the sodium for potassium chloride, so it counts
None of this makes potassium frightening. It makes it a mineral worth respecting. Eat it freely from food, and check your kidney markers before you decide a capsule is the answer.
Frequently asked questions
Is it safe to take a potassium supplement?
For a healthy adult with normal kidney function, a low dose is generally well tolerated. The NHS says 3,700mg or less a day is unlikely to have obvious harmful effects. It turns risky when your kidneys clear potassium poorly, or when you take a medicine that raises it. Ask your GP or pharmacist first.
Does Helvy test potassium?
No. Potassium shifts quickly and is best measured by your GP as part of a urea and electrolytes test. Our panels measure the kidney filtration markers instead, which are urea, creatinine and eGFR. Those describe how well your kidneys clear potassium, which is the underlying question.
What are the symptoms of low potassium?
Muscle weakness, cramps, constipation, tiredness and a fluttering heartbeat are the common ones. They are vague, and many other things cause them. Low potassium usually comes from vomiting, diarrhoea or water tablets rather than diet. A blood test at your GP settles it.
How much potassium do I need a day?
The NHS says adults aged 19 to 64 need 3,500mg a day. Potatoes, beans, pulses, leafy greens and bananas are the usual sources. Food delivers it slowly, with water and fibre. That is why it does not carry the risk a concentrated capsule does.
Can potassium lower my blood pressure?
Potassium contributes to the maintenance of normal blood pressure. That is an authorised claim on the GB Nutrition and Health Claims Register, and it describes the nutrient in a normal diet. It is not a promise that a capsule will bring down a high reading. Never change a blood pressure medicine on the strength of a supplement.
Your kidneys decide whether potassium is safe for you
Our Thyroid & Vital Organs panel (£159) measures urea, creatinine and eGFR alongside your thyroid, liver and full cholesterol breakdown. Home finger-prick kit, results usually within 5 working days of the lab receiving your sample, from UKAS-accredited UK laboratories.
Medical disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Helvy does not sell potassium supplements and does not measure potassium.
Blood tests measure biomarkers; they do not diagnose disease. The research cited reports population averages and may not predict your own response. Do not start, stop or change any medicine or supplement based on this article. Speak to your GP, your pharmacist or a qualified healthcare professional. All Helvy blood tests are processed by UKAS-accredited UK laboratories to ISO 15189.
Last updated: August 2026 · By Helvy · Medically analysed at UKAS-accredited UK laboratories
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