Obesity May Up Risk of Kidney Failure

May 22, 2006 -- New research shows that people who have ever been obese may be more likely to develop chronic kidney failurekidney failure (chronic renal failure, or CRF).

?ObesityObesity seems to be an important -- and potentially preventable -- risk factor for CRF,? write Elisabeth Ejerblad, MD, and colleagues in June?s Journal of the American Society of Nephrology.

Ejerblad works at Sweden?s Karolinska Institute. Her study included 926 people with chronic kidney failure and 998 people of similar backgrounds without chronic kidney failure. Among the findings:

• Being overweight at age 20 tripled the odds of chronic kidney failure.
• Men who had ever been obese and women who had ever been very obese were 3 to 4 times as likely as those who had never been obese to have CRF.

About Kidney Failure

Here?s how the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), a branch of the National Institutes of Health, describes the kidneys and kidney failure:

• The kidneys are a pair of bean-shaped organs, each about the size of a fist, in the middle of the back, just below the rib cage.
• The kidneys filter waste products and extra water out of the blood; those waste products and water become urine.
• Kidneys may fail suddenly (acute kidney failure) or gradually.
• Chronic kidney failure is the gradual loss of kidney function.
• Total or near-total kidney failure is called end-stage renal disease, which requires kidney dialysis or transplantation.

Warning Signs

The early stages of kidney diseasekidney disease may not show symptoms. The first signs may include frequent headaches or feeling tired or itchy all over your body. Those symptoms aren?t unique to kidney failure and may or may not indicate kidney failure.

The NIDDK lists these possible symptoms of worsening kidney failure:

• Needing to urinate more or less often
• Appetite loss or nausea and vomiting
• Swollen or numb feet and hands
• Feeling drowsy or having trouble concentrating
• Darkening skin
• Muscle cramps

Doctors may test blood and urine samples to look for signs of kidney problems.

Studying Kidney Failure

Participants in Ejerblad?s study were in their late 50s, on average, and lived in Sweden.

Most had ?moderately severe? chronic kidney failure, the researchers write. The study doesn?t show that any of the patients had end-stage renal disease or were on dialysis.

Participants completed mailed questionnaires covering these topics:

• Height
• Current weight
• Weight at 20, 40, and 60 years
• Highest lifetime weight
• Education
• Alcohol consumption
• Tobacco use

Participants were also interviewed in person and had their medical records checked. The researchers calculated participants? body mass index (BMI)body mass index (BMI), which is based on height and weight.

BMI of 30 or more is considered obese. BMI of at least 25 but less than 30 is considered overweight. There are other ways to measure obesityobesity, but this study (like many others) only tracked BMI.

Weight, Kidney Failure

Few participants had been obese at age 20. But those who had BMI of 25 or more at that age were three times as likely to have chronic kidney failure during the study.

There was nothing magic about being 20 years old. Having ever been obese tripled to quadrupled men?s odds of having chronic kidney failure during the study, compared with men with a BMI of less than 25.

Women were a bit different. If they had ever been what the researchers call ?morbidly obese? (BMI of at least 35), they were three to four times more likely to have chronic kidney failure during the study, compared with women with a BMI of less than 25.

The links between excess weight and chronic kidney failure were strongest for diabetesdiabetes-related kidney problems but also applied to other types of chronic kidney failure. The patterns included patients who reported not having diabetes or high blood pressurehigh blood pressure, two conditions that make chronic kidney failure more likely.

Study?s Limits

It?s possible that some participants may have had high blood pressure or diabetes and not known it, the researchers point out.

In the U.S., high blood pressure and diabetes are common, and a lot of people don?t know they have those conditions. The CDC estimates that in 2005, 20.8 million people in the U.S. had diabetes and that 6.2 million of them have undiagnosed diabetes. According to the American Heart Association, recent estimates have shown that one in three U.S. adults have high blood pressure but almost a third of them don?t know it.

Participants in Ejerblad?s study may not have reported their weight perfectly. For instance, several decades may have passed since participants were 20 years old, the youngest age for which they reported weight.

Current BMI wasn?t linked to chronic kidney failure. That result may be due to weight lossweight loss associated with chronic kidney failure, note Ejerblad and colleagues.

SOURCES: Ejerblad, E. Journal of the American Society of Nephrology, June 2006; vol 17. WebMD Public Information from the National Institutes of Health: ?Your Kidneys and How They Work.? CDC: ?National Diabetes Fact Sheet, United States, 2005.? American Heart Association: ?High Blood Pressure.? News release, American Society of Nephrology.