Lowering BMI Will Also Reduce the Burden of Kidney Disease

Strong Evidence for Causal Link Between Obesity and Renal Decline

SAN DIEGO—The prevalence of obesity in the United States and worldwide has been increasing during the past 30 years, and studies have consistently shown a connection between obesity and kidney disease. New evidence suggests that focused efforts to combat obesity may dramatically decrease kidney disease–related morbidity, adding one more instrument to physicians’ “tool box” by encouraging patients to lose weight.

Paul Muntner, MD, of Tulane University School of Public Health and Tropical Medicine, New Orleans, presented new data at the American Society of Nephrology annual meeting that highlighted a causal link between obesity and a decline in renal function. Dr Muntner emphasized that the data show a strong, graded relationship between increased body mass index (BMI) and kidney disease in humans.

He noted that obese persons are 7 times more likely to develop diabetes and 2 to 3 times more likely to develop hypertension—the 2 leading causes of kidney disease. Obesity is also associated with other risk factors for kidney disease, including inflammatory markers and lipid abnormalities.

Obesity has been linked to insulin resistance, which, in turn, can lead to increased oxidative stress, nitric oxide synthesis, endothelial dysfunction, vascular smooth muscle cell proliferation, and heightened salt sensitivity. These factors contribute to the worsening of renal hemodynamics and the development of glomerulosclerosis.

In the 1970s, massive obesity was identified as a cause of proteinuria consistent with kidney disease. Pathologic changes associated with morbid obesity have since been identified, including focal segmental glomerulosclerosis with glomerulomegaly.

“Obesity rates have been steadily increasing, and so we need to be aware of what is coming down the road,” Dr Muntner tells IMWR. “The million dollar question is how can the internist affect his or her patients’ habits such that they can control or lower their weight? We still don’t know, but telling the patients that they are at increased risk for diabetes, high blood pressure, heart disease, and kidney disease may help motivate some patients.”

This study gives primary care physicians another reason to discuss weight issues with their obese patients, explain how their weight is affecting their kidneys in the long-term, and what steps to take to lower their overall risk for chronic kidney disease and its morbid consequences.

Dr Muntner stressed that there is now incontrovertible evidence that obesity is a direct cause of kidney disease; it is not merely an association found in a laboratory or suggested in epidemiologic studies. He advised that presenting the facts in a clear, concise manner may help patients better understand the process and become more motivated to deal with their weight problem.

“Obesity is a causal risk factor. It is not just something we think from our studies is associated with chronic renal disease. It is more like cigarette smoking. We know smoking causes lung cancer and a host of other diseases. We now have evidence that has been growing for the past 20 years that shows a cause-and-effect relationship between obesity and kidney disease.”

Key points

• Increasing evidence shows a cause-and-effect relationship between obesity and kidney disease.

• Obesity is associated with several risk factors for kidney disease, including diabetes, hypertension, inflammatory markers, and hyperlipidemia.

• Unless physicians intervene, the obesity epidemic could spur a kidney disease epidemic.