Researchers at the University of California, San Francisco ( UCSF ) have determined that there is a strong relationship between being obese and developing end-stage renal disease, or kidney failure.
The long-range study found that the obese have up to a seven times greater risk of kidney failure than normal weight people, suggesting that obesity should be considered a risk factor for the condition, and that kidney failure is yet another consequence of obesity.

" There are more and more people with kidney failure, but it hasn't been appreciated much that kidney failure can be a consequence of obesity," said Chi-yuan Hsu, lead author of the study. " We think this study is important because it demonstrates quite convincingly that people who are obese or overweight are at much higher risk of kidney failure."

The study, published in the Annals of Internal Medicine, was conducted jointly with Kaiser Permanente of Northern California Division of Research.

Research findings showed that being even moderately overweight nearly doubles the risk of developing the condition, which is a complete failure of the kidneys to process waste so that dialysis or transplantation become necessary.

" If you are mildly overweight, not even frankly obese, you are roughly 90 percent more likely to develop end-stage renal failure," Hsu said, with the risk reaching over 700 percent greater for the morbidly obese.

The research is based on data derived from over 320,000 Northern California Kaiser members whose height and weight were measured during health checkups between 1964 and 1985.
A total of 1,471 cases of end-stage renal disease occurred among study participants during an average follow-up period of about 26 years.
Cases of end-stage renal disease were determined using the U.S. Renal Data System, a comprehensive national registry that collects and disseminates information on end-stage renal disease.

Researchers calculated the body mass index ( BMI ) of study participants and found that those with a higher BMI were at greater risk of kidney failure.

Of the study participants, 58 percent were of normal weight and 39 percent had a BMI of 25 or greater. The risk of kidney failure among "overweight" study participants was 1.87 times that of normal weight participants, or nearly 90 percent greater. The most obese study participants, with a BMI of 40 or above, had over seven times the risk of kidney failure.

More than 400,000 Americans receive long-term kidney dialysis and more than 20,000 have a functioning transplanted kidney.

Traditional risk factors for end-stage renal disease are high blood pressure and diabetes, Hsu said. But the study found that obesity remained a risk factor, even after adjustment for blood pressure and diabetes status. Most kidney doctors don't think of weight loss as a potential way of reducing kidney failure, he added. The study suggests that kidney doctors should calculate their patients' BMI when evaluating their risk of kidney failure.

Hsu said one reason for the higher rate of kidney failure among obese patients might be that they are more likely to develop diabetes and hypertension. Another reason is that obesity places more metabolic demand on the kidneys, forcing them to work harder. "As the person gets bigger, hyper-filtration occurs and this over filtration is what tears the kidneys down."

Source: University of California – San Francisco, 2006


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