New research led by alumnae of the Harold Amos Medical Faculty Development Program (AMFDP) offers new insights into the development of kidney problems among young adults, even those who show no symptoms. AMFDP is a program of the Robert Wood Johnson Foundation.
Vanessa Grubbs, MD, MPH, Kirsten Bibbins-Domingo, MD, PhD, and a team of eight other researchers studied the relationship between body mass index and early decline of kidney function. They reached two important conclusions: First, using the right measures, clinicians should be able to detect the beginning stages of some kidney problems earlier than is now common; and second, obesity is tightly associated with kidney function decline, even in the absence of high blood pressure, diabetes, and other weight-related conditions that are known drivers of kidney disease.
Together with their colleagues, the two AMFDP alumnae analyzed patient data from CARDIA (Coronary Artery Risk Development in Young Adults), a multi-city, longitudinal research project that has tracked the health of a diverse group of young adults since the mid-1980s. The research team categorized 2,891 people in the data set into four body mass index ranges: normal weight, overweight, obese, and extremely obese.
Then, rather than using the more common measure of creatinine as a gauge for kidney function, researchers used data on patients’ cystatin-C protein levels, a more sensitive measure of the rate at which kidneys are doing their blood-filtering work.
At the beginning of the 10-year period examined, all of the patients in the study had kidney function in the normal range. Over time, average kidney function diminished in all groups, but it decreased most rapidly among the heaviest patients.
On its own, that finding was not surprising, since the heavier patients were more likely to develop conditions such as blood pressure, inflammation, and even diabetes that would take a toll on kidney function. But when the researchers screened the data for such factors, they found that higher BMI on its own was still associated with greater diminution of kidney function. “When we accounted for diabetes, high blood pressure, and inflammatory processes,” Grubbs says, “the body mass index was still a predictor of kidney function decline, so there was something unique about just being too large that, in and of itself, affected kidney function even before the onset of clinically apparent kidney disease.”
That could mean that some unidentified factor related to weight causes kidney function decline, or that the weight itself somehow burdens the kidneys. Whatever the specific cause, Grubbs says, “the point is that we can see these things starting to happen at a significant rate in these young adults, even before we would ordinarily start paying attention clinically. If we’re going to intervene early to prevent all the adverse effects of chronic kidney disease, we need to start looking at those indicators.”
From Research to Practice
Bibbins-Domingo observes that while the findings offer clinicians a way to identify likely candidates for kidney problems before symptoms arise, new approaches will be required. “Our challenge is in the way clinicians think about obesity,” she says. “When we have patients who are obese, we don’t necessarily see disease yet. That usually happens later on. So the hope is for more awareness among clinicians, and also patients, that those extra pounds are actually taking a toll on all the organ systems at that very moment, even among young adults. We hope that will prompt clinicians to have the conversations with patients. ... The potential is that during young adulthood one could make a change that could change the trajectory.”
Grubbs notes that recognizing weight-related kidney function decline early on is only one part of the puzzle for patients and clinicians. The next challenge is to help patients change what are often lifelong habits around eating and exercise. “It’s very difficult,” she says. “I try to counsel patients about obesity, but a lot of the time, we don’t really get anywhere. So I’d hope this kind of research will help give patients one more incentive to lose weight, and sustain the weight loss. And I also hope this would contribute to work by other researchers trying to fill in the gaps about how we can actually make a difference with helping our patients lose weight.”
The findings also puncture the notion of being “overweight but healthy,” Grubbs points out. “We’ve all heard people, even morbidly obese people, say, ‘Well, I went to the doctor, and I don’t have health problems related to weight yet, so I think things are fine.’ This study suggests that it’s not just fine. Just being that large alone, even if you don’t have other chronic issues, is a problem.”
The findings also point to new topics for research, Bibbins-Domingo observes. “We’re still learning all the mechanisms by which weight gain affects all the other systems,” she says. “The study adds lines of research to be developed in this area, and highlights a new organ to focus on: the kidney.” Such research could explore the mechanisms by which weight affects kidney function, she says, as well as whether and how to intervene clinically with younger adults who display early signs of kidney decline, with an eye toward helping them lose weight or to protecting their kidneys from the effects of their weight.
Grubbs and Bibbins-Domingo’s study, “Body Mass Index and Early Kidney Function Decline in Young Adults: A Longitudinal Analysis of the CARDIA (Coronary Artery Risk Development in Young Adults) Study,” was published online on November 29, 2013, in the American Journal of Kidney Disease.
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