Supplements and kidney disease: what builds up, which herbs to avoid, and why vitamins for CKD come on prescription

Why some supplements build up when kidneys are weak

Your kidneys filter the blood and send what the body doesn’t need into the urine. That includes extra minerals, water-soluble vitamins and many plant compounds. The US National Kidney Foundation (NKF) points out that some herbal supplements leave the body through the kidneys, so levels can become toxic when the kidneys work poorly. Labels rarely mention this.

Kidney problems become more common with age, and chronic kidney disease (CKD) is usually picked up on a blood test rather than by how you feel. If you buy supplements for a parent, ask whether their GP has ever mentioned “kidney function” or “eGFR”.

Kidney Care UK specifically says not to take supplements containing vitamins A or E, and not to buy vitamin D yourself: the kidney team checks levels and may prescribe a form such as alfacalcidol.

eGFR basics: what your kidney numbers mean

Your GP estimates kidney function with a blood test called eGFR (estimated glomerular filtration rate). It shows roughly how many millilitres of blood your kidneys filter per minute. A urine test, ACR (albumin:creatinine ratio), shows whether protein is leaking into the urine. Together they set the stage.

For ACR, A1 is under 3 mg/mmol, A2 is 3–30 and A3 is over 30. A higher stage on either scale means more serious disease. Find your result to see what it means for supplements:

One trap: creatine. eGFR is calculated from creatinine, a breakdown product of creatine. A creatine supplement raises creatinine and can make your kidneys look worse than they are. Our creatine guide explains more.

Herbal remedies: why “natural” doesn’t mean safe for kidneys

The best-known warning comes from Belgium. In the early 1990s, young women who took slimming pills with Chinese herbs from one Brussels clinic developed fast-progressing kidney damage. The cause was aristolochic acid, which had got into the pills by mistake. About 30–45% of those affected later developed cancer of the urinary tract.

Aristolochic acid is now classed as a human carcinogen and banned in many countries. NKF notes it still turns up in some traditional remedies, and Kidney Care UK warns that products bought online may contain it, as well as lead and mercury.

Herbs that NKF lists as high risk for people with kidney disease include:

• liquorice root, which Kidney Care UK says can raise blood pressure and affect potassium;
• aristolochia (birthwort, wild ginger);
• astragalus, bearberry (uva ursi), cat’s claw, chaparral and comfrey;
• horsetail, stinging nettle, parsley root and Java tea;
• St John’s wort, yohimbe and creatine.

After a kidney transplant the stakes are higher. Herbs can interact with anti-rejection medicines and, as Kidney Care UK puts it, increase the chance of your body rejecting the kidney. Its examples include CBD with tacrolimus and schisandra. It also warns that taking lots of turmeric over a long time raises the chance of kidney stones.

NKF advises avoiding anything sold as a “kidney detox” or “kidney cleanse”, and blends that don’t state the amount of each ingredient.

Prescribed renal vitamins vs a shop multivitamin

People with CKD sometimes need vitamins, because a kidney diet that limits protein, potassium or phosphorus can also cut vitamin intake. NKF notes that products combining B vitamins and vitamin C for people with CKD are available on prescription. Kidney Care UK says B vitamins and vitamin C are usually safe, but warns that vitamin C doses over 500 mg can cause harm because the chance of kidney stones goes up.

An ordinary multivitamin is a different thing. It usually contains vitamin A, often vitamin E, minerals such as magnesium and phosphorus, and sometimes herbal extracts. Tap the lines on a typical label to see what your kidney team would look at:

What to ask your kidney team

The 2024 KDIGO guideline (the international standard for CKD care) asks clinicians to review and limit over-the-counter medicines and herbal or dietary remedies that may be harmful. It also asks for regular medicine reviews, including when your care changes. You can make that easy:

1. Bring every bottle, or a photo of each label, to your next appointment. NKF suggests this so the team can check the ingredients.
2. Include sleep aids and painkillers. Kidney Care UK warns that diphenhydramine in some sleep aids can build up with kidney disease and raise the risk of falls.
3. Ask which supplements to stop, which to keep, and whether anything should be prescribed instead.
4. Ask the renal dietitian about potassium, phosphorus and protein before changing your diet.
5. Write the answers down. Our medicines list for your GP works for the kidney clinic too.

A weekly pill organiser helps keep prescribed tablets and any approved supplements in order.

Who should be especially careful

• anyone with CKD stage 3 or above, or with protein in the urine;
• people on dialysis or with a kidney transplant;
• people taking blood pressure tablets that affect potassium, such as ramipril, losartan or spironolactone;
• older people taking several medicines at once;
• anyone with a history of kidney stones.

For this group, even common products such as magnesium, electrolyte drinks and calcium need a yes from the kidney team first.

How to use iHerb safely if you have kidney disease

1. Don’t add anything new until your kidney team has seen the label.
2. Use the Supplement Facts photo on the product page to show the team exactly what’s inside.
3. Skip proprietary blends and “kidney detox” products.
4. Avoid products with vitamin A, vitamin E, potassium or high-dose vitamin C unless prescribed.
5. If you’re unsure where to start, our vitamin check flags kidney disease, and the 50+ section covers other medicine questions.