CHICAGO (Reuters) - An increasingly aging U.S. population is faced with growing obesity-related problems ranging from disabilities to chronic kidney disease, researchers said on Tuesday.

"Obesity is more hazardous to the health of the elderly than we previously suspected," said Dawn Alley of the University of Pennsylvania School of Medicine, whose study appears in the Journal of the American Medical Association.

"For an older person, suffering from obesity means they are much less likely to be able to walk to the front door or pick up a bag of groceries," she said.

A second report from Johns Hopkins University in the same journal found that chronic kidney disease is on the rise in the country because of increases in obesity, high blood pressure and diabetes, leading to more demand for kidney dialysis and organ transplants.

The study from Pennsylvania, which compared data from a government health survey involving nearly 10,000 people age 60 and over, found obesity on the increase along with the inability to walk a few blocks or even take 10 steps, stoop, lift a moderate amount of weight, walk between rooms or stand up from an armless chair.

Such functional impairment did not change significantly among normal-weight individuals, but increased among the obese by 5.4 percent, rising to 42.2 percent of people studied between 1999 to 2004, compared with 36.8 percent in a sample five years earlier.

"We believe that two factors are likely contributing to the rise in disability among older, obese people," said Dr. Virginia Chang, who also worked on the study.

"First, people are potentially living longer with their obesity due to improved medical care, and second, people are becoming obese at younger ages than in the past. In both instances, people are living with obesity for longer periods of time, which increases the potential for disability," she said.

The kidney disease study, based on U.S. government health surveys involving more than 28,000 people, found the prevalence of chronic kidney disease rose to 13 percent of those studied in 1999-2004, compared with 10 percent of those studied in 1988-1994.

But awareness of the problem remains low among the general public.

The researchers attribute the increase to an aging U.S. population and rising rates of obesity, which can lead to diabetes and high blood pressure.

The presence of chronic kidney disease is determined by measuring persistent, excess protein in urine and the amount of fluid filtered by the kidneys.

Tracking what leads to end-stage kidney disease is crucial, "particularly given the increase in the prevalence of obesity, diabetes and hypertension, the leading risk factors for chronic kidney disease," the researchers wrote.

(Reporting by Michael Conlon; editing by Julie Steenhuysen and Todd Eastham)