Diuretic herbs and the kidney

Boerhavia diffusa, punarnava, is used in classical Ayurveda for oedema, for urinary conditions and as a general rejuvenative. Several other preparations are used similarly.

The kidney deserves particular care in this area, for reasons that are well documented.

The most important precedent

Aristolochic acid nephropathy is the clearest case of harm from a traditional herbal preparation, and it should inform how this whole category is approached.

In the early 1990s, a cluster of cases of rapidly progressive kidney failure appeared among women attending a weight-loss clinic in Belgium. Investigation traced it to a herbal preparation in which a species containing aristolochic acid had been substituted for another.

Aristolochic acid causes irreversible kidney damage and urothelial cancer. Many affected patients required dialysis or transplantation, and a high proportion subsequently developed urinary tract cancers.

Similar cases were subsequently identified in other countries, and the compound has been linked to endemic kidney disease in parts of the Balkans where the plant contaminates wheat fields.

Aristolochic acid-containing plants are used in several traditional systems including Ayurveda. Many countries have banned them.

The relevant lessons: species substitution is a real and dangerous problem, kidney damage can be silent until advanced, and traditional use did not detect this harm because the delay was years.

Why the kidney is particularly vulnerable

The kidneys receive a large proportion of cardiac output and concentrate substances during filtration, which means compounds reach high concentrations in kidney tissue.

Kidney damage is frequently asymptomatic until substantial function is lost. Someone can lose a large proportion of kidney function without symptoms.

And kidney damage is frequently irreversible.

Which is a poor combination: high exposure, silent progression, and no recovery.

Herbal preparations and the kidney more generally

Reviews of herbal nephrotoxicity have identified a number of implicated plants and preparations, and cases of acute kidney injury attributed to herbal products appear regularly in the literature.

Mechanisms include direct toxicity, interstitial nephritis, obstruction from crystal formation, and contamination with heavy metals — which affect the kidney among other organs.

People with existing kidney disease are at substantially higher risk, because impaired clearance means higher exposure, and because they have less reserve.

The diuretic issue specifically

Preparations with genuine diuretic activity raise several concerns.

Electrolyte disturbance, particularly potassium, which affects cardiac rhythm.

Dehydration and volume depletion, which can itself precipitate acute kidney injury, particularly in older people or in hot weather.

Additive effects with prescribed diuretics, which is a real interaction concern.

Interaction with lithium, where diuretics increase lithium levels and can cause toxicity.

Masking the cause of oedema. This is arguably the most important. Fluid retention is a symptom, and its causes include heart failure, kidney disease, liver disease, thyroid disease, venous insufficiency and medication effects.

Treating the swelling without identifying the cause delays diagnosis of conditions where treatment matters. Heart failure in particular has treatments that reduce mortality substantially, and delay costs.

What the evidence shows for punarnava

Limited. Laboratory and animal studies report diuretic and other activities. Human clinical trials are few and small.

Reviews have described the evidence as preliminary.

This is the general position for most traditional preparations used for kidney and urinary conditions.

Practical guidance

Do not self-treat oedema. New or worsening swelling requires medical assessment to identify the cause. Swelling with breathlessness is urgent. Swelling in one leg with pain or warmth may indicate a clot and is urgent.

If you have kidney disease, do not take herbal preparations without discussing them with your kidney doctor. This is one of the clearest cases where the risk-benefit calculation is unfavourable.

Check for aristolochic acid. Products should not contain plants known to contain it, and species names on labels are the only way to check. Products without botanical names should not be taken.

Insist on heavy metal testing for any traditional preparation, and particularly if you have any kidney impairment.

Tell your doctor, particularly if you take diuretics, lithium, or medications affecting kidney function.

Stay hydrated, particularly if taking anything with diuretic activity, and be cautious in hot weather.

What protects kidney function

Blood pressure control, which is the single most important intervention. Diabetes control. Avoiding unnecessary non-steroidal anti-inflammatory drugs, which are a common cause of kidney injury. Adequate hydration. Not smoking. And regular monitoring if you are at risk, since early detection allows intervention before substantial function is lost.

A simple blood and urine test detects kidney disease long before symptoms, which is exactly why it is worth having if you have diabetes, hypertension or a family history.

New swelling, reduced urine output, or blood in urine require medical assessment. Do not take herbal preparations if you have kidney disease without specialist advice. Check botanical names and avoid any product containing aristolochia species.