By: Lisa Rapaport

(Reuters Health) – Obese people have an increased risk of kidney disease even when they don’t have health problems like high blood pressure or elevated blood sugar that can impair renal function, a large Korean study suggests. 

In otherwise healthy individuals, obesity was linked to 6.7 more cases of kidney disease for every 1,000 people over five years than occurred among normal-weight patients. Being overweight was associated with 3.5 more cases per 1,000. 

The findings contradict some previous research that has found people with what’s known as “metabolically healthy obesity” may not face an increased risk of kidney problems, cardiovascular disease or other issues linked to excess weight, said lead study author Dr. Yoosoo Chang of Kangbuk Samsung Hospital Total Healthcare Center in Seoul. 

“Obese individuals who are considered 'healthy' because they don’t currently have heart disease or metabolic risk factors should not be assumed healthy,” Chang said by email. 

“The presence of obesity appears to be enough to increase a person’s risk of future chronic kidney disease as well as other obesity-associated diseases including heart disease,” Chang added. “It’s important that people maintain a healthy weight and lifestyle to prevent future obesity-related complications.”

Globally, 1.9 billion adults are overweight or obese, according to the World Health Organization. Obesity increases the risk of heart disease, diabetes, kidney complications, joint disorders and certain cancers.

Risk factors for kidney disease include hypertension, diabetes, obesity, smoking, elevated cholesterol and high blood sugar as well as family history and advanced age.

To assess how weight might influence the odds that patients develop chronic kidney disease, Chang and colleagues analyzed data on more than 62,000 young and middle-aged people. 

About 59 percent of the participants were normal weight at the start of the study, while 21 percent were overweight, 13 percent were obese and 7 percent weighed too little.

People were about 36 years old at the start of the study, and they were followed for an average of six years. 

The link between obesity and kidney disease was more pronounced among older people in the study. 

Among those under age 40, obesity was associated with 3.5 more cases of kidney disease for every 1,000 people than occurred with normal-weight patients over five years. But after 40, the increased risk connected to obesity jumped to 19 cases per 1,000 people.

One limitation of the study is that researchers identified obese people using data on body mass index (BMI), a ratio of weight relative to height that doesn’t distinguish between fat and muscle, the authors note. They also lacked data on how long people were obese or how weight changed over time. 

Even so, the findings suggest that doctors should warn obese patients about the risk of kidney disease and encourage them to make lifestyle changes to shed excess pounds, the authors conclude in Annals of Internal Medicine. 

Because some previous studies have tied obesity to better survival among patients with advanced kidney disease and fewer deaths from cancer and cardiovascular disease, however, more research is still needed to pinpoint the exact nature of the relationship between weight and kidney problems, noted Dr. Georges Nakhoul of the Cleveland Clinic Glickman Urological and Kidney Institute in Ohio. 

“The idea of 'healthy obesity' came from the observation that patients with chronic diseases such as end stage renal disease appear to have an improved survival when their BMI is elevated,” Nakhoul, who wasn’t involved in the study, said by email. 

“Obesity being a known cardiovascular risk factor, this finding was somewhat counter-intuitive and hence has been named 'the obesity paradox,'” he said.

SOURCE: Annals of Internal Medicine, online February 8, 2016.

Originally Published: Reuters