Which supplements with renal insufficiency?

Why does renal insufficiency worsen the risk of toxicity of food supplements?

What happens in a kidney that no longer filters correctly?

A failing kidney no longer eliminates excess substances quickly enough, which accumulate in the blood and alter the internal balance of the human body. The physiological role of the kidney, a central organ of the filtration system, is to filter around 180 litres of plasma per day to eliminate urea, potassium, phosphates, oxalates and drug residues via the glomerular vessels. When the glomerular filtration rate (GFR) drops, these waste products accumulate. Every additional intake (vitamin, mineral, amino acid, plant) then increases the load on already saturated nephrons. The review by Dori et al. (Revue Médicale Suisse, 2014)^[2], carried out at the CHUV Nephrology Service in Lausanne (internal medicine), has documented this mechanism. Supplementation products can cause acute and chronic failures, sometimes irreversible, especially in patients with undiagnosed latent CKD^[1].

From which stage do supplements become risky?

The critical threshold is a GFR below 60 ml/min/1.73 m², i.e. stage 3 of the KDIGO 2024 classification^[3]. Above this threshold, the kidney retains a functional reserve sufficient to handle the majority of usual dietary intakes. Below it, the elimination of each compound becomes slowed: the organ can no longer buffer overloads, even moderate ones, and the progression of chronic kidney disease speeds up. The problem is worsened by under-diagnosis. Recent international studies show that around 80% of patients at stages 1-2 and 71% at stage 3a are unaware of their CKD (Lange 2021, German cohort)^[2]. A person at stage 3a (GFR between 45 and 59 ml/min/1.73 m²) can feel in perfect health and consume supplementation products for months before developing an acute decompensation that justifies emergency care.

Which mineral and vitamin supplements are contraindicated in case of renal insufficiency?

Why do potassium, magnesium and phosphorus expose to cardiac emergencies?

The diseased kidney no longer correctly eliminates electrolytes: their accumulation exposes to potentially fatal rhythm disorders, which justifies particular attention to the diet of patients with CKD. Hyperkalaemia (blood potassium above 5.5 mmol/L)^[3] is the most feared emergency. It can be triggered by multivitamin formulas concentrated in potassium, salt substitutes based on potassium chloride or effervescent magnesium-potassium combinations — to which is added the consumption of naturally rich foods such as certain fruits (banana), vegetables (spinach, potatoes) and dried beans. Magnesium and phosphorus follow the same logic. A magnesium supplementation of 300 to 400 mg per day, banal in a healthy subject, becomes toxic at stage 4 (GFR below 30 ml/min/1.73 m²). It can then cause hyporeflexia and bradycardia. Phosphorus, present in large quantities in high-protein products and foods containing phosphate additives, contributes to the mineral and bone disorders of CKD, the progression of which low-protein diets help to limit (Pereira et al., Nutrients, 2024)^[4].

Why are high-dose vitamin C and unsupervised vitamin D risky?

Ascorbic acid in excess turns into oxalate, which precipitates as crystals in the tubules. From 500 mg per day taken regularly, this compound is partly metabolised into oxalic acid. A review by Karr et al. (Integrative Medicine, 2024)^[6] estimates that this metabolism generates 35 to 55% of circulating oxalates in adults. A clinical case published by Raja et al. (Cureus, 2023)^[5] describes an acute oxalate nephropathy in a diabetic patient managed in a hospital setting. The patient had followed a liquid diet based on juice and water for a week for upper gastrointestinal haemorrhage. The biopsy confirmed the diagnosis and several dialysis sessions were initiated. Vitamin D poses the opposite problem: its metabolism depends on the kidney, which converts 25-hydroxyvitamin D into its active form. In advanced CKD, this conversion collapses, and an excessive dose exposes to hypercalcaemia and to calcium deposits in tissues^[3].

Which protein supplements and plants are not advised in case of renal insufficiency?

Why do whey, creatine and amino acids overload the diseased kidney?

High-protein products increase the production of urea and creatinine, overloading a kidney whose purifying capacity is already reduced — an effect that adds to the intakes coming from protein-rich foods (red meat, poultry, fish, fromage blanc, eggs). A meta-analysis by Chen et al. (Journal of Nephrology, 2024)^[7], on 16 randomised trials and 1,344 patients at stages 3 to 5, confirms that a low-protein diet supplemented with ketoanalogues slows the decline of the GFR. It also improves calcium-phosphate homeostasis. Conversely, the unsupervised free intake of whey or amino acids speeds up the progression in the at-risk patient, with no demonstrated benefit on muscle mass in this population. Creatine poses a specific dilemma. The Swiss review by Dori et al. (2014)^[2] cites it among the products documented as nephrotoxic in case of pre-existing CKD. The failing organ metabolises it poorly and converts it into accumulated creatinine.

Which medicinal plants can cause acute renal insufficiency?

Several plants common in herbal medicine are documented as nephrotoxic and constitute a genuine iatrogenic pathology when consumed without professional advice. Aristolochia (Aristolochia fangchi) is the archetype of this: it contains aristolochic acid, which causes progressive interstitial fibrosis and a risk of urothelial carcinoma^[2]. Its sale is banned in Switzerland as in the European Union. Red yeast rice (Beni-koji) is banned by the FSVO^[8] both as a foodstuff and as a medicine. In Japan, several case series published in 2024 describe Fanconi syndromes with proximal tubular damage (Habuka et al., BMC Nephrology, 2024)^[9]. Liquorice, through its glycyrrhizin, induces a pseudo-hyperaldosteronism: sodium retention, potassium loss, raised blood pressure (Penninkilampi et al., J Hum Hypertens, 2017)^[10].

• ⚠Aristolochia (Aristolochia fangchi): banned in Switzerland, irreversible interstitial fibrosis.
• ⚠Red yeast rice (Beni-koji): banned by the FSVO, Fanconi syndrome documented by biopsy.
• ⚠Liquorice (Glycyrrhiza glabra): pseudo-hyperaldosteronism beyond 100 mg/day of glycyrrhizin (LOAEL, Penninkilampi 2017).

What to do if you already take food supplements with degraded renal function?

How to screen for renal insufficiency before supplementation?

Screening relies on a blood measurement of creatinine (with calculation of the estimated GFR) and a urinary examination (albumin/creatinine ratio) prescribed by the general practitioner. These two tests, inexpensive and reimbursed in Switzerland, allow the function of the kidney to be classified according to the KDIGO 2024 stages (1 to 5)^[3]. The Swiss CHUV recommendations^[1] advise systematic screening in those over 60, in type 2 diabetics and in patients with arterial hypertension, and before any prolonged intake of supplementation products. A frequent warning sign is foamy urine, a sign of proteinuria; ankle oedema, persistent fatigue and unexplained rise in blood pressure also warrant a check-up, which may be accompanied by therapeutic education and tailored dietary advice.

Which reflexes to adopt in case of confirmed CKD?

The first reflex is the immediate discontinuation of any non-prescribed product and the introduction of a balanced diet with a low content of potassium and phosphorus, adapted by a healthcare professional. Several of the clinical cases cited (ascorbic acid, red yeast rice, liquorice) show an improvement in kidney function, sometimes complete, after simple discontinuation — but some progress to end-stage renal failure (end stage requiring dialysis or transplantation) when stopping is delayed^[9]. The second is the nephrology consultation to assess whether certain supplementations remain justified (ketoanalogues, activated vitamin D, iron in case of anaemia) and to preserve the patient’s quality of life. Sports products (whey, creatine, BCAA) are advised against without medical opinion. The FSVO 2024 national campaign led to the banning of 113 products out of 127 checked (89%)^[8]. Patients on treatment (ACE inhibitors, sartans, diuretics) must consult a professional before the introduction of any new formula.

Frequently asked questions