DEAR DOCTOR K:
I have high blood pressure and diabetes. I was surprised to learn that they increase my risk of kidney disease. How do they do that?
Many people know that high blood pressure and diabetes increase the risk of getting heart disease. But less well known is the fact that they are also powerful risk factors for kidney disease.
The kidneys filter toxins and wastes from the bloodstream, flushing them out of the body in urine. At the same time, they hold on to important proteins and other useful substances. This process helps control levels of fluid, salt and acid in the body. The kidneys also play an important role in regulating blood pressure.
Blood flows into your kidneys through the renal arteries, which branch into successively smaller blood vessels. They end in small clusters of tiny blood vessels (capillaries). The capillaries form little tufts known as glomeruli. (I’ve put an illustration of this below.)
Prolonged exposure to high blood sugar, as occurs in diabetes, causes capillary membranes to thicken. This damages and distorts the delicate filtering mechanisms of the glomeruli. High blood pressure scars and weakens the kidney’s blood vessels. The bottom line: Both conditions damage the capillaries, and thereby interfere with the kidney’s ability to filter blood. In fact, diabetes is the leading cause of kidney failure. High blood pressure is not far behind.
How the kidneys work
Blood flows into your kidneys through the renal arteries, which branch into successively smaller blood vessels, finally ending in small clusters of capillaries known as glomeruli. Each cluster, or glomerulus, is part of a nephron—a tube-like structure that filters and purifies the blood. Each kidney has more than a million nephrons.
Controlling your blood pressure and blood sugar protects your heart, your brain, your eyes, your nerves — and your kidneys. Fortunately, some of the most widely used blood pressure drugs not only lower blood pressure but also directly protect the kidneys from injury. These include ACE inhibitors and angiotensin-receptor blockers.
Lifestyle changes such as not smoking, maintaining a healthy body weight and getting regular exercise help you control both high blood pressure and diabetes. For this reason, they also help protect you against getting kidney injury. Your doctor may also recommend that you limit sodium and protein in your diet. This will further help preserve kidney function.
If you develop kidney disease, one problem (of many) that you and your doctor will be faced with is that damaged kidneys aren’t able to efficiently clear medications from the body. You must work closely with your doctor to find the proper dosage of any medicines you take — including many of the medicines you take for diabetes and high blood pressure. Otherwise, toxic levels may build up and cause dangerous side effects.
Another problem with developing kidney disease is that this makes it harder to control your blood pressure. Injured kidneys make a chemical that raises blood pressure. So it’s a vicious cycle: High blood pressure injures the kidneys, and injured kidneys make blood pressure higher. So you really want to prevent kidney injury in the first place.
Finally, always check with your doctor before taking herbal supplements or over-the-counter pain relievers. Some, including nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil) and naproxen (Aleve), may harm your kidneys.