How does sugar affect the kidneys?

Sugar is not a problem for the kidneys unless your blood sugar level gets too high. This commonly occurs in both type 1 and type 2 diabetes. Once the blood sugar level gets higher than 180 milligrams per deciliter (mg/dL), the kidneys start to spill sugar into the urine. The higher the blood sugar, the more sugar comes out in the urine. If your kidneys are normal, this usually isn’t a problem, but if you have diabetes, too much sugar can cause kidney damage.

A common blood test used to detect diabetes and monitor blood sugar levels over time involves the hemoglobin A1C (HgbA1C) protein. The higher the blood sugar gets, the more sugar gets attached to this protein. Determining the levels of hemoglobin A1C helps to give an estimate of the average sugar level in the blood for the past three months and provides an indication of how much damage the sugar may be causing in the body, including to the kidneys. A normal HgbA1C is less than 6% for someone who doesn’t have diabetes. As the HgbA1C gets higher, more damage is done.

Uncontrolled diabetes can damage the blood vessels of the kidneys and destroy their filters. When the blood vessels in the kidneys are injured, the kidneys can’t clean the blood properly, resulting in more water and salt being retained and waste materials building up in the blood.