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Ask Dr. K: Control blood sugar to avoid kidney damage

DEAR DOCTOR K: I have Type 2 diabetes. My doctor said that kidney disease is a potential long-term complication of diabetes. What’s the connection between the two?

DEAR READER: People with diabetes have elevated levels of blood sugar. Left untreated or poorly treated, diabetes can cause serious complications, such as eye, nerve and kidney damage. An important cause of all these complications is high blood sugar levels over many years. Other factors, such as high blood pressure, also contribute.

But the long-term consequences of diabetes are not inevitable. They can be prevented through tight blood sugar control.

High levels of blood sugar injure the walls of small blood vessels. They thicken and leak. The vessels may eventually clog, blocking blood flow to vital organs.

You asked about kidney disease. The main function of the kidneys is to filter out toxic substances and waste matter from blood so they get flushed out of the body when we pass urine. And they keep important proteins and other useful substances inside the body. They also regulate fluid, salt and other minerals, so that just the right amounts of each remain in the body. The filtering work is done by glomeruli, delicate networks of tiny blood vessels.

When the blood vessels that form the glomeruli — the filters — thicken, they begin to fail at their job. Protein leaks into the urine. Fluid, salt and some other minerals build up in the body.

In addition, the damaged glomeruli stop filtering out wastes and toxins reliably. These wastes and toxins build up in the bloodstream, causing damage to tissues and organs throughout the body. (I’ve put an illustration on my website, AskDoctorK.com.)

The best way to avoid diabetes complications is to keep your blood sugar levels as close to normal as possible. Adjust your therapy if your HbA1c level (which measures average blood sugar levels over a three-month period) is 7 percent or higher. And keep your blood pressure under 130/80 mm Hg. This, too, helps prevent kidney damage.

Many years ago, I had a patient, Jane, with diabetes who was showing early signs of kidney disease. She was not very careful about measuring her blood sugar, nor about taking her diabetes medicines. Since early kidney disease generally doesn’t cause symptoms, she felt fine.

I introduced her to another patient of mine, Barbara, who also had not been careful about her treatment, and who went on to develop end-stage kidney failure. She required kidney dialysis treatments three times a week to keep her alive.

Barbara told Jane: “These dialysis treatments are keeping me alive. But it’s still a pain in the * to lie here three times a week for several hours while the machine works on my blood. And I don’t feel all that good. I’m alive, but that’s about it.”

Jane started to get more serious about her diabetes and never developed kidney failure. She was glad I’d introduced her to Barbara.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.

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