It’s long been known that people with diabetes, especially after living with the condition for a number of years, are at increased risk for kidney disease. That’s because elevated blood glucose levels can damage the tiny blood vessels in your kidneys, leading to reduced kidney function over time.
But the relationship also works in the opposite direction, according to a recent study from Washington University School of Medicine in St. Louis and the Veterans Affairs St. Louis Health Care System.
Researcher Ziyad Al-Aly, MD.
“We’ve always thought that diabetes can cause kidney disease, but we’ve never really thought the other way around,” until this study, notes lead author Ziyad Al-Aly, MD.
First large study in humans
The study, published in December 2017 in the journal Kidney International, was inspired by previous animal studies showing that blood levels of a substance called urea nitrogen — which are higher in cases of kidney disease — are associated with the risk of developing diabetes, says Al-Aly.
“Urea itself both suppresses insulin secretion and reduces insulin sensitivity,” Al-Aly notes. “It makes the body less responsive to the action of insulin.”
To examine the effect of urea levels on later development of diabetes, Al-Aly and colleagues looked at medical records of over 1.3 million veterans without diabetes enrolled in the Veterans Health Administration. The records covered a five-year period beginning in 2003.
At the beginning of the study period, about 9% of participants had elevated blood urea levels, indicating poor kidney function. By the end of the study, those with elevated urea levels were 23% more likely to have developed diabetes. This increased risk was found to be progressive, meaning that the higher participants’ urea levels were, the more likely they were to develop diabetes.
What Is Urea?
• Urea (measured as blood urea nitrogen, or BUN) is a normal byproduct of protein metabolism in your body.
• It’s removed from your blood by your kidneys and excreted in your urine.
• But when kidney function is reduced, higher levels of urea can build up in your blood.
(Source: National Kidney Foundation)
Lessons and limitations
As you might expect in a veteran population, men made up the overwhelming majority of participants in this study. But that doesn’t mean the results in women were unclear. “When we do a ‘big data’ approach like this and we have a sample of 1.3 million people,” Al-Aly says, “5% female is more than 50,000 people” — a large enough group of women to ensure an accurate analysis.
A potential limitation of the study is that people with kidney disease are likely to have more interactions with the health-care system, which means that diabetes may be more easily detected in this group. To account for this effect, Al-Aly and his colleagues statistically controlled for measures of health-care use, but it’s still possible that these corrections didn’t fully account for the effect of greater contact with the health-care system.
It’s also unclear what this study means for people looking to reduce their risk of developing diabetes. “If we reduce urea or change it, does that reduce the risk of diabetes? The answer is likely to be yes,” Al-Aly says. “But we’re at the beginning stages of figuring out that relationship.”
For now, Al-Aly says, it’s possible that certain recommended dietary changes — like reducing your intake of red meat, if it’s too high — could lower your blood urea levels. But it’s too early to make any new behavioral recommendations, based just on this one study.
One message, though, is clear — avoiding kidney disease can also help you avoid diabetes.
Want to learn more about avoiding kidney disease? Read “Kidney Disease: Your Seven-Step Plan for Prevention.”