No Such Thing as 'Fat and Fit'? High BMI Associated With CKD

Pam Harrison

February 09, 2016

Overweight and obese men and women who are otherwise metabolically healthy are still at increased risk of developing chronic kidney disease (CKD) over an average follow-up of 6 years compared with normal-weight patients, a large cohort study of South Korean participants indicates.

"I would expect that in Western populations, the risk of CKD increases with increasing body mass in metabolically healthy subjects as well, so our findings suggest that weight control should be recommended for obese participants even if they still do not show any metabolic effects of increased adiposity," senior author Eliseo Guallar, MD, professor of epidemiology and medicine, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, told Medscape Medical News.

"Our study demonstrates that...metabolically healthy obesity is not a harmless condition…and that the obese phenotype, regardless of metabolic abnormalities, can adversely affect renal function."

The study was published online February 8 in the Annals of Internal Medicine, by Yoosoo Chang, MD, PhD, of Kangbuk Samsung Hospital, Seoul, Korea, and colleagues.

"Physicians should monitor metabolically healthy obese and overweight patients for CKD and counsel them about maintaining a healthy weight and lifestyle," the researchers stress.

Asked to comment, Bessie Young, MD, MPH, professor of medicine, University of Washington, Seattle, told Medscape Medical News that she has issues with the study, principally the fact that the investigators did not adequately describe how they defined CKD among study participants.

CKD Consistently Higher in Overweight, Obese Subjects

The Kangbuk Samsung Health Study involved a cohort of South Korean men and women 18 years of age and older who had received an annual or biennial health examination at the Kangbuk Samsung Hospital Health Screening Center between January 2002 and December 2008.

All participants had at least one follow-up visit as well.

Patients with any evidence of metabolic abnormalities, including elevated fasting glucose levels, blood pressure, lipids, or indices of insulin resistance or any indication of renal dysfunction (estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73 m2) were excluded.

The final sample included 62,249 participants, all of whom were metabolically healthy and who had no evidence of CKD at baseline.

Renal function was assessed by a single measurement at each visit.

The mean age of the cohort was 36.1 years and the mean body mass index (BMI) was 22.1 kg/m2.

During an average follow-up of 6 years (36,088 person-years of follow-up) 906 participants developed CKD, with an overall incidence rate of 2.5 cases per 1000 person-years

The cumulative 5-year incidence of CKD was consistently higher in participants with higher BMIs, even after multivariate adjustment for a variety of confounders, including age, sex, year of screening examination, smoking status, alcohol intake, and physical activity at baseline.

On the other hand, there were four fewer cases of CKD per 1000 persons in participants who were underweight compared with normal-weight subjects.

Adjusted Difference in 5-Year Cumulative Incidence of CKD (Asian-Specific Criteria)

Group (BMI)
Cases per 1000 persons
Underweight (< 18.5 kg/m2) -4.0
Normal weight (18.5–22.9 kg/m2) Reference group
Overweight (23–24.9 kg/m2) 3.5
Obese (≥ 25 kg/m2) 6.7

In addition, heavier participants developed CKD more rapidly than normal-weight participants, Dr Guallar added.

"In fact, metabolically healthy obese subjects reached a 1% incidence of CKD 2.4 years earlier than normal-weight metabolically healthy participants," she said.

Differences in CKD risk among the different BMI categories were also larger among participants 40 years of age or older at the start of the study.

For example, the incidence of CKD reached a high of 19 cases per 1000 participants for patients 40 years of age and older at baseline who were in the highest BMI category relative to their normal-weight counterparts.

The researchers say it is not known specifically how obesity is linked to kidney damage independent of metabolic risk factors, but possible mechanisms include hemodynamic changes, oxidative stress, and hormonal effects.

CKD Definition Not Clearly Described

In commenting on the study particulars, Dr Young told Medscape Medical News that "people want to read how CKD is defined very clearly," as this is "a key feature," of this type of research, and "there can be some issues if CKD is not defined well."

CKD is traditionally defined as an eGFR of < 60 mL/min/1.73 m2 for 3 months or more and/or the presence of albuminuria or proteinuria, she noted.

Furthermore, when evaluating the same relationship between obesity and CKD in US-based populations, "obesity defined by a high BMI has not been associated with incident CKD once people adjust for many things like baseline eGFR and other risk factors," she pointed out.

The authors and Dr Young had no relevant financial relationships.

Ann Intern Med. Published online February 8, 2016.Abstract

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