People who have diabetes have a higher risk of kidney disease. When you hear those words, you might imagine kidneys that don’t work well enough. But in the early stages of diabetes, something surprising can happen: The kidneys may filter too much. In other words, they’re working more than they should. This is called hyperfiltration, and it shows how the body’s attempts to adapt to high blood sugar can sometimes have unintended consequences.
Your kidneys contain millions of tiny filtering units called nephrons. As blood passes through them, water, salt and glucose (sugar) are filtered out of the blood. The kidneys then decide what to return to the bloodstream and what should eventually leave the body as urine.
Normally, almost all the glucose that enters this filtered fluid is returned to the blood. One protein that helps with this job is called SGLT2. It moves glucose back into the body along with sodium, a major component of salt.
When your blood sugar is high, more glucose reaches the kidneys. The kidneys respond by trying to hold on to more of it. As they reabsorb more glucose, they also reabsorb more sodium.
That’s where things get interesting.
Farther along the kidneys’ filtering system are specialized cells that monitor how much salt reaches them. Think of these cells as a checkpoint that helps determine whether the kidneys are filtering the right amount of blood.
Because the kidneys reabsorb more sodium along with glucose, less sodium reaches this checkpoint. The kidneys can interpret this as a signal that they aren’t filtering enough.
Their response? Filter more.
Blood flow and pressure within the kidney’s tiny filters change, causing filtration to increase. In the short term, that may not sound like a bad thing. But more filtration doesn’t necessarily mean healthier kidneys.
Working harder isn’t always working smarter, even if you’re a kidney.
Imagine turning up the water pressure through a delicate household filter. It might move more water, but constantly operating under higher pressure can put stress on the filter. Something similar can happen in the kidneys. Over time, this increased workload and pressure may contribute to kidney damage.
Medications called SGLT2 inhibitors can protect the kidneys. They reduce the amount of glucose and sodium that the kidneys accumulate. Taking this medication helps more sodium reach the kidneys’ “checkpoint,” helping restore its normal feedback signal. Then the kidneys stop filtering so much.
Your kidneys are hard workers, but even they shouldn’t be working overtime.
Nicholas Blackmond, MS, is a PhD trainee in kinesiology at Wayne State University School of Medicine. His academic interests focus on cardiovascular and renal physiology, cardiometabolic disease and translational research that bridges basic science and clinical application. Blackmond enjoys helping broad audiences see how physiology connects to everyday life and health.