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Obesity can cause higher kidney stone risk.

Researchers at the University of Texas-Southwestern Medical Center at Dallas have found that the more overweight people are, the higher the risk of uric acid kidney stones.

For the first time, these findings directly link excess body weight with uric acid kidney stones. These stones are found in about 5 percent of patients with kidney stones and in about 30 percent of diabetic patients with kidney stones.

"This is yet another price to pay for being overweight or obese," said Dr. Khashayar Sakhaee, program director of the university's General Clinical Research.

It is estimated 10 percent of people in the U.S. will be subject to a kidney stone at some point in their lives.

These stones are solid deposits that form from substances excreted in urine. When waste materials in urine do not dissolve completely, microscopic particles begin to form and over time grow into "stones." These stones may remain in the kidney, or they may break loose and travel down the urinary tract. Small stones may pass out of the body naturally, but a larger stone can become trapped in a ureter, the bladder, or the urethra, possibly blocking the flow of urine and often causing intense pain.

Uric acid kidney stones develop when the acid level of the urine is too high, typically from the ingestion of too much dietary animal protein or when there are insufficient amounts of buffers to neutralize acid in the urine.

The latest study, which included researchers at the University of Chicago, tracked nearly 5,000 kidney stone patients in Dallas and Chicago. Results did not vary between men and women or among patients who restricted the types of foods eaten.

"Larger people have very acidic urine even when they control their diets," said Dr. Sakhaee, professor of internal medicine at the university. "For the first time, we are advising weight loss as part of our therapy. That connection had not been made in the past."

A study published by the university in the February 2004 issue of Kidney International concluded that uric acid stones are also associated with insulin resistance and type-2 diabetes. Heavier people tend to have more insulin resistance, too, said Dr. Orson Moe, a co-author of the earlier report.

According to Dr. Charles Y. C. Pak, senior author of the current study and professor of internal medicine, the discovery of a link between body weight and uric acid kidney stone formation is significant.

"In 1986 we coined the term 'gouty diathesis' to describe uric acid stones forming in the absence of any discemible cause," Dr. Pak said. "We now know that one of the causes is obesity that leads to insulin resistance and diabetes. The challenge for our research team is to determine whether weight loss and/or sensitization to insulin would bring about a relief of stone formation."

(Source: Kidney International April 2004.)
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Publication:Nutrition Health Review
Geographic Code:1U7TX
Date:Dec 22, 2003
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