Your kidneys filter about 50 gallons of blood every day, removing waste and balancing fluids. A surprisingly long list of common habits, medications, and health conditions can quietly damage them, often without symptoms until significant harm has already occurred. Understanding what puts your kidneys at risk is the first step toward protecting them.
High Blood Sugar and High Blood Pressure
Diabetes and high blood pressure are the two leading causes of kidney disease, and they often work together. Persistently elevated blood sugar generates a flood of reactive oxygen species (essentially, toxic byproducts) that injure the tiny filtering units inside each kidney. Over time, this triggers inflammation, scarring, and a breakdown of the delicate capillary walls that separate your blood from your urine. The filters start leaking protein that should stay in your bloodstream, and the kidney gradually loses its ability to clean your blood efficiently.
High blood pressure damages kidneys through a different but equally destructive route. Your kidneys have a built-in pressure regulation system that shields their fragile capillaries from the full force of your blood pressure. When blood pressure stays elevated for years, or when kidney disease has already begun impairing that protective mechanism, the excess pressure physically injures blood vessel walls. This is called barotrauma. The resulting scarring of the kidney’s filters, known as glomerulosclerosis, increases in direct proportion to how high your blood pressure climbs. Keeping blood pressure controlled is one of the most effective ways to slow kidney decline.
Pain Relievers and Common Medications
Over-the-counter painkillers like ibuprofen and naproxen (NSAIDs) are among the most widely used medications that can harm kidneys. These drugs work by reducing blood flow to the kidneys as a side effect of how they block inflammation. Occasional use at standard doses is generally safe for people with healthy kidneys, but high cumulative doses over weeks or months raise the risk of both acute kidney injury and long-term kidney damage.
The risk jumps significantly when NSAIDs are combined with certain blood pressure medications or water pills (diuretics). This combination can trigger acute kidney injury within the first 30 days of use. In some cases, NSAIDs can also cause a type of kidney inflammation that develops weeks to months after you start taking them regularly. If you rely on these painkillers frequently for chronic pain, it’s worth discussing alternatives that are easier on your kidneys.
Other medications that can stress the kidneys include certain antibiotics, some heartburn drugs (proton pump inhibitors used long-term), and the contrast dye used in CT scans and cardiac catheterizations. Contrast dye poses the greatest risk to people who already have reduced kidney function: patients with significantly impaired filtration face up to a 30% chance of kidney injury after receiving it. Age over 75, dehydration, and diabetes all compound that risk.
Not Drinking Enough Water
Chronic dehydration is the single biggest risk factor for kidney stones. When you don’t drink enough fluid, your urine output drops, and the concentration of minerals and waste products in your urine rises. At high enough concentrations, those minerals crystallize and bind together to form stones. Small stones can pass painfully on their own, but larger ones may block urine flow and cause swelling that damages kidney tissue.
Beyond stones, consistently low fluid intake forces your kidneys to work harder to concentrate urine and clear waste. Over years, this added strain contributes to gradual decline in kidney function. There’s no magic number for daily water intake that applies to everyone, but producing pale yellow urine throughout the day is a reliable sign you’re drinking enough.
Too Much Sodium
A high-sodium diet raises blood pressure, which circles back to the blood vessel damage described above. But sodium also harms kidneys more directly by increasing the amount of protein that leaks through damaged filters, accelerating the progression of existing kidney disease. The recommended limit for people with kidney disease is 2,000 mg of sodium per day, roughly the amount in one teaspoon of table salt. Most people consume well over that without realizing it, since the majority of dietary sodium comes from processed and restaurant foods rather than the salt shaker.
High-Protein Diets With Existing Kidney Problems
If your kidneys are healthy, a high-protein diet is unlikely to cause damage on its own. But if you already have reduced kidney function, excess protein creates a real problem. When your body breaks down protein, it produces waste products like urea that the kidneys must filter out. Damaged kidneys can’t keep up with that waste load, so the byproducts accumulate in your blood. This is why people with kidney disease are often advised to moderate their protein intake, even though the same restriction isn’t necessary for the general population.
Herbal Supplements and Vitamins
Some supplements marketed as “natural” are genuinely toxic to kidneys. The most notorious are herbs containing aristolochic acid, found in certain traditional Chinese medicine preparations. These have been directly linked to severe, irreversible kidney damage and were pulled from the U.S. market. But the list extends well beyond those. Documented kidney-toxic supplements include thundergod vine, tribulus, wormwood, St. John’s wort, impila, and Chinese yew extract.
Even common supplements can cause harm at high doses. Excessive vitamin A, vitamin C, and vitamin D have all appeared in case reports of kidney injury. Creatine, chromium, and glucosamine are also on the list of dietary supplements linked to kidney toxicity. The lack of regulation in the supplement industry means products may contain unlisted ingredients or doses far higher than what’s on the label. If you take multiple supplements regularly, it’s worth checking whether any of them are on the known nephrotoxic list.
Certain foods also pose risks in specific situations. Star fruit, for example, is toxic to people who already have chronic kidney disease, even though it’s harmless to those with normal kidney function.
Smoking and Alcohol
Smoking damages kidneys by constricting blood vessels, reducing blood flow to the kidney’s filtering units, and accelerating the hardening of arteries that supply them. Smokers with diabetes or high blood pressure face a compounded risk, since all three conditions attack the same vulnerable capillary networks. Quitting smoking slows the rate of kidney function decline measurably.
Heavy alcohol consumption raises blood pressure and can cause acute kidney injury during episodes of binge drinking. Chronic heavy drinking also leads to liver disease, which in turn disrupts the hormonal signals that regulate kidney function. Moderate drinking (one drink per day for women, two for men) has not been clearly linked to kidney harm in people with otherwise healthy kidneys.
How Kidney Damage Shows Up
The frustrating reality is that kidneys can lose a significant portion of their function before you feel anything. The earliest detectable sign is usually protein leaking into your urine, something you can’t see or feel. A simple urine test measures this: a normal result is less than 30 mg/g on the albumin-to-creatinine ratio. Results between 30 and 299 mg/g signal early kidney damage and a higher risk of kidney failure, heart failure, and stroke. At 300 mg/g or above, kidney disease is likely already established.
Later symptoms include swelling in your ankles and feet, fatigue, foamy urine, and needing to urinate more frequently at night. By the time these symptoms appear, kidney function is often significantly reduced. Routine blood work and urine tests, especially if you have diabetes, high blood pressure, or a family history of kidney disease, catch problems at the stage where they’re most treatable.