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How Your Kidneys Work and Why They Matter — The Organs You Cannot Live Without

By Health 656 Editorial Team 2026-03-24 8 min read

Medical professional discussing kidney health

You have two kidneys, each the size of a fist, sitting on either side of your spine just below the rib cage. Every day they filter roughly 150 liters of blood — your entire blood volume passes through them 30 to 40 times. They remove waste, balance electrolytes, regulate blood pressure, control red blood cell production, and maintain the acid-base balance that keeps you alive. Chronic kidney disease affects 37 million Americans — roughly 15 percent of the adult population — and 9 in 10 do not know they have it according to the CDC. Kidney disease is called the silent epidemic because it produces no symptoms until roughly 70 to 80 percent of function is lost. This guide explains how your kidneys work, what damages them, and what you can do to protect them.

What Your Kidneys Do — Far More Than Filter Blood

Each kidney contains roughly 1 million tiny filtering units called nephrons. Blood enters each nephron through a cluster of capillaries called the glomerulus, where water, electrolytes, glucose, amino acids, and waste products are filtered out under pressure. As the filtrate flows through the tubule, useful substances (glucose, amino acids, most water and electrolytes) are reabsorbed back into the blood, while waste products continue through and become urine. This filtration-reabsorption process runs continuously, filtering roughly 150 liters of blood daily and producing 1-2 liters of urine.

But filtration is only one of five critical jobs. Blood pressure regulation: The renin-angiotensin-aldosterone system (RAAS), controlled by the kidneys, adjusts sodium and water retention to maintain blood pressure. This is why kidney disease causes hypertension, and why ACE inhibitors and ARBs (which target RAAS) are the preferred blood pressure medications for kidney protection. Red blood cell production: Kidneys produce erythropoietin (EPO), which signals bone marrow to make red blood cells. Kidney failure causes anemia because this signal weakens. Vitamin D activation: Kidneys convert vitamin D to its active form — needed for calcium absorption and bone health. Acid-base balance: Kidneys maintain the precise pH of blood (7.35-7.45). Even small deviations are life-threatening.

A 55-year-old electrician learned he had stage 3 chronic kidney disease during a routine physical. His creatinine was elevated and his eGFR was 42. He had no symptoms. "I felt completely normal," he said. "If I had not had that blood test, I would have found out when I needed dialysis. By then it would have been too late to slow it down."

What Damages Your Kidneys

Diabetes is the number one cause of kidney failure — high blood sugar damages the delicate glomerular capillaries over years, progressively reducing filtration capacity. High blood pressure is number two — sustained high pressure damages kidney blood vessels and overworks the nephrons. Together, diabetes and hypertension account for 75 percent of all kidney failure cases according to the National Kidney Foundation.

Other damaging factors: chronic NSAID use (ibuprofen, naproxen) — reduces blood flow to the kidneys, particularly dangerous when combined with dehydration. Recurrent kidney infections. Kidney stones causing prolonged obstruction. Autoimmune conditions (lupus nephritis, IgA nephropathy). Smoking (reduces kidney blood flow by 15 percent according to a study in the American Journal of Kidney Diseases). Genetic conditions (polycystic kidney disease, affecting 1 in 1,000 people).

Warning Signs — Usually Too Late

Kidneys have enormous reserve capacity. Symptoms typically do not appear until 70-80 percent of function is lost — meaning kidney disease can progress silently for years or decades. By the time symptoms emerge, the damage is extensive and largely irreversible.

Late-stage symptoms include: persistent fatigue and weakness (from anemia). Swelling in legs, ankles, and around eyes (fluid retention). Foamy urine (protein leaking through damaged filters — a sign of glomerular damage). Reduced urine output. Persistent itching (waste buildup in blood). Nausea, loss of appetite, and metallic taste. Shortness of breath (fluid overload). Difficulty concentrating. Muscle cramps (electrolyte imbalances).

This is why screening is critical. A simple blood test (creatinine with estimated GFR) and urine test (albumin-to-creatinine ratio) can detect kidney disease years before symptoms. The National Kidney Foundation recommends annual screening for everyone with diabetes, hypertension, family history of kidney disease, or age over 60.

How to Protect Your Kidneys

Control blood sugar and blood pressure — these two actions prevent the majority of kidney disease. A1C below 7 percent and blood pressure below 130/80 are the targets. Every 1 percent A1C reduction reduces kidney complications by 37 percent (UKPDS). Stay hydrated — 2-3 liters of water daily supports kidney function and reduces kidney stone risk. Limit NSAID use — chronic ibuprofen or naproxen damages kidneys, especially when dehydrated or combined with other kidney-stressing medications. Use acetaminophen for chronic pain when possible.

Do not smoke — smoking reduces kidney blood flow and accelerates damage from diabetes and hypertension. Get screened — annual creatinine, eGFR, and urine albumin for anyone with risk factors. Eat a balanced diet — the DASH diet benefits both blood pressure and kidney health. Reduce excessive sodium. If you already have kidney disease, manage potassium and phosphorus intake with your nephrologist's guidance.

New medications: SGLT2 inhibitors (dapagliflozin, empagliflozin) — originally developed for diabetes — have been shown to reduce CKD progression by 30-40 percent in landmark trials (DAPA-CKD, EMPA-KIDNEY), and are now recommended for CKD patients even without diabetes. This is one of the most significant advances in kidney medicine in decades.

Common Questions

Can kidney damage be reversed?

Acute kidney injury (from dehydration, medication, or infection) is often reversible. Chronic kidney disease (from years of diabetes or hypertension damage) is generally not reversible but can be slowed or stabilized with treatment. The earlier CKD is detected and managed, the better the outcomes.

Do I need to drink 8 glasses of water a day?

The 8-glass rule has no strong scientific basis. Adequate hydration varies by body size, activity, and climate. A practical target: drink enough to keep urine pale yellow. Roughly 2-3 liters of total fluid daily is reasonable for most adults. Increase during heat, exercise, and illness.

Can I live with one kidney?

Yes. A single healthy kidney can perform the work of two with minimal long-term health consequences. This is why living kidney donation is possible and safe. The remaining kidney enlarges slightly and increases its filtration rate to compensate.

How do I know if my kidneys are healthy?

A blood test (serum creatinine with estimated GFR) and a urine test (albumin-to-creatinine ratio) are the two screening tests. GFR above 90 with no protein in urine indicates healthy kidney function. These tests should be included in routine annual blood work for anyone with risk factors.

kidneys kidney-function GFR creatinine prevention

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