April 26, 2001 -- Just as railroads and airlines charge extra for heavy cargo, the human body exacts a heavy price for obesity in the form of heart disease and diabetes. And with the major rise in body size seen in the U.S. and other western nations over the last 15 years, there has been a 10-fold increase in a serious form of kidney disease called obesity-related glomerulopathy.
"We had a definite subjective sense that the incidence of this disease was increasing, and we put it to the test by actually looking at our numbers and indeed we show a 10-fold increase in the incidence over a 15-year period," says Vivette D. D'Agati, MD, professor of pathology at Columbia University College of Physicians and Surgeons in New York.
D'Agati and colleagues studied nearly 7,000 kidney biopsy samples collected over a 15-year period, and found that the incidence of obesity-related glomerulopathy, or ORG, jumped from 0.2% of all samples taken from 1986 to 1990, to 2% of all samples taken from 1996 to 2000. That leap is significant enough for the researchers to title the report of their study in April's Kidney International "An Emerging Epidemic".
The increase in ORG coincides with a sharp increase in rates of obesity in the U.S. According to the National Health and Nutrition Examination survey, nearly one-fourth of Americans are obese, defined as a body mass index (height to weight ratio) greater than 30. The survey also found that more than half of Americans are overweight, defined as a BMI greater than 25.
"One of the first things we showed in this paper that has not been described before is that there is also an association of this disease with submorbid obesity; in other words, patients who have [mild-to-moderate] obesity," D'Agati tells WebMD.
The researchers found that the patients with ORG had an average BMI greater than 41, putting them in the category of morbidly obese. With the excess pounds come increased risk for high blood pressure, heart disease, insulin-resistance, and type 2 diabetes, all of which can have adverse effects on the kidneys as well.
The kidneys are highly complex organs that serve essential functions. They constantly filter blood to remove nitrogen and other waste products, respond to the body's ever-changing demands for water, regulate concentrations of minerals and salts in the blood, and help to maintain the body's balance of acids and bases. Although we can function normally with only one healthy kidney, failure of both kidneys is a life-threatening event requiring immediate action such as hemodialysis (use of artificial kidneys), or kidney transplantation.
There is ample evidence to suggest that carrying around all that extra weight eventually takes a toll on the kidneys, says Jeffrey R. Henegar, PhD, associate professor of pathology at the University of Mississippi Medical Center in Jackson.
"It's well established that obesity is related to diabetes -- in fact 80% of diabetics are type 2, and those are almost all people who are at least overweight if not obese. And then we've shown in the past eight or nine years that ... in normal healthy individuals blood pressure goes up ... with a fairly substantial increase in weight, and if you lose weight blood pressure comes back down. The contention is that over a period of time there's going to be a detriment to the kidneys," says Henegar, who was not involved in the Columbia study.
In the kidney, blood filtration occurs primarily in the glomeruli, microscopic raspberry-shaped tangles of blood vessels The glomeruli let small molecules such as waste products escape from the bloodstream out into the urine for removal from the body while keeping larger molecules (such as useful proteins) in circulation.
One sign that kidneys are diseased is proteinuria, or spilling of excess proteins into the urine. In some cases, proteinuria can signal progressive disease that could lead to kidney failure.
Fortunately, D'Agati and Henegar tell WebMD, in at least some cases the proteinuria seen in people with ORG can be halted or reversed with weight loss and/or the use of blood-pressure lowering drugs called ACE-inhibitors.
"We had a few patients where the proteinuria improved with the weight loss," D'Agati says, "We had five patients that had what we consider to be significant weight loss, losing up to 36% of their original weight. Four of those patients had no other therapy and in all four patients we described a decline in the proteinuria by at least 50%."