Study links obesity to kidney failure

Researchers have found a strong relationship between obesity and kidney failure.

The obese are nearly twice as likely as thinner folk to develop kidney disease and the risk for the morbidly obese is seven-fold higher, says a US study.

The link could be because obesity is linked to hypertension and diabetes, which could eventually lead to end-stage renal failure, said author Chi-yuan Hsu, an assistant professor of medicine at the University of California, San Francisco, and lead author of the study. Obesity also makes the kidneys work harder, he said.

End-stage renal failure is a breakdown in the ability of the kidneys to process waste. At that point, dialysis or transplantation is necessary. More than 400,000 Americans receive long-term kidney dialysis and the number of people who suffer from end-stage renal disease is projected to increase to more than 650,000 by 2010, with associated Medicare expenditures of $28 billion, the study said.

The findings of the study add to a growing list of health problems related to obesity. The study, published in the Annals of Internal Medicine, is the first to show convincingly the tie between weight and kidney disorders.

Obesity has long been linked to heart disease, high blood pressure and diabetes, among other ailments. Now kidney failure should be added to the list.

Kidney failure happens very slowly. As the body gets bigger, it tends to retain more water and this over-filtration is what tears the kidneys down.

The study assessed data derived from over 320,000 members of the Kaiser Permanente insurance plan in northern California whose height and weight were measured during health checkups between 1964 and 1985. About 1,471 cases of end-stage renal disease occurred among study participants during an average follow-up period of 26 years.

Obese people weren't the only subjects found to be at risk. Hsu said. “If you are mildly overweight, not even frankly obese, you are roughly 90 percent more likely to develop end-stage renal failure."

Researchers calculated the body mass index of study participants and found generally that those with a higher BMI were at greater risk of kidney failure. BMI is weight in kilograms divided by height in meters squared. A BMI of over 25 defines a person as being overweight, over 30 defines them as being obese and over 40 is considered by health professional to be “morbidly obese."

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. Kidney failure is ninth among the leading causes of death in the United States, with an annual death rate of about 20 percent a year.