Obese young adults at risk for developing kidney disease are largely unaware of the looming problem, a U.S. study suggests.

Researchers examined more than a decade of data on almost 7,000 people aged 20 to 40 years and found more than one-third had what's known as abdominal obesity, or belly fat.

They also looked at data on lab tests to detect elevated levels of the protein albumin in the urine, which signals that kidneys aren't functioning properly and indicates a heightened risk for developing chronic kidney disease.

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Not many people had elevated albumin levels, but less than 5 percent of those who did have this risk factor said they had been told about the problem.

"The take-home message for young adults is that abdominal obesity, which we know is associated with diabetes and high blood pressure, is also associated with early signs of kidney disease," said senior study author Dr. Michal Melamed of the Albert Einstein College of Medicine and Montefiore Medical Center in New York.

To explore the connection between abdominal obesity and kidney disease risk, Melamed and colleagues examined lab tests results for albumin and survey data collected from 1999 to 2010 on race, ethnicity and waist circumference.

They defined abdominal obesity as a waist circumference of 35 inches (88 centimeters) in women and 40 in (102 cm) in men.

Among Mexican-American participants, 40 percent had abdominal obesity and 11 percent of those with excess fat around the waist had elevated albumin levels. That compares to just 3.6 percent of Mexican Americans without abdominal obesity, researchers report in the journal PLoS ONE.

The differences were less stark among non-Mexican Americans.

Among white participants, 37 percent had abdominal obesity and about 6 percent of these individuals had high albumin levels while almost 5 percent of those without big waists had high albumin.

With black participants, 45 percent had abdominal obesity and about 7 percent of these people had elevated albumin, compared to 5 percent without abdominal obesity.

When Mexican Americans had abdominal obesity - even when they didn't have early signs of diabetes or high blood pressure - they were more than four times as likely as others to have high albumin.

This suggests that abdominal obesity may somehow damage kidney function even before people develop other conditions like diabetes and high blood pressure, which are known causes of kidney damage, the authors conclude.

The study can't prove abdominal obesity does cause kidney damage, only that there's a link between belly fat and one risk factor for kidney problems, the authors caution. Another limitation of the study is its lack of data on dietary and genetic differences across races that might contribute to a risk of kidney damage.

Even so, the findings add to a growing body of evidence suggesting that not only overall obesity, but the location of excess fat stores, can influence the risk for metabolic diseases, said Dr. Laura Rosella, a public health researcher at the University of Toronto who wasn't involved in the study.

"It is important to note that people with extra body weight overall also tend to have extra weight in the midsection - so achieving a healthy body weight should be a priority," Rosella said by email.

"The message that is important for young people is that the earlier excess weight starts to accumulate, the early it starts negatively affecting your metabolic risk for many diseases, including kidney disease," Rosella added.

SOURCE: http://bit.ly/1TRzaZx PLoS ONE, online May 25, 2016.