Older, Overweight Dialysis Patients Benefit From "Obesity Paradox"

Nancy A. Melville

November 29, 2010

November 29, 2010 (Denver, Colorado) — In a phenomenon known as the obesity paradox, obesity, commonly associated with poorer health outcomes, is associated with a lower mortality risk among kidney dialysis patients. However, new research throws a twist into the paradox — it does not appear to apply to younger patients, but rather to those 65 years and older.

In a prospective multicenter cohort study, presented here at Renal Week 2010: American Society of Nephrology 43rd Annual Meeting, researchers from the Netherlands evaluated 7-year mortality data on 1749 dialysis patients from the Netherlands Cooperative Study on the Adequacy of Dialysis (NECOSAD), found that young patients (<65 years) who were obese had a 50% increased risk of dying within 7 years, compared with normal-weight young patients.

In contrast, obesity was not associated with increased mortality for elderly dialysis patients (>65 years).

Underweight patients, with a body mass index (BMI) below 20 kg/m2, had higher rates of mortality in both the younger and older groups than those in the normal-BMI group.

Both younger and older dialysis patients who were underweight had about a 2-fold increased risk for mortality, and younger obese patients had about a 1.6-fold increased risk for mortality, compared with those of normal weight.

"Younger dialysis patients who were underweight had greater mortality compared to those with normal weight, and in contrast to the older patients, obese younger patients had a greater mortality risk than those with normal weight. Therefore, the obesity paradox does not hold for younger dialysis patients," said Ellen Hoogeveen, MD, PhD, from the Jeroen Bosch Hospital, in Den Bosch, the Netherlands.

"Elderly obese patients, meanwhile, did not have an increased risk of mortality," Dr. Hoogeveen said.

Patients' relative risk was adjusted for age, sex, smoking, cardiovascular disease, and mode of dialysis.

The patients were divided into 8 categories on the basis of age (younger and older than 65 years) and baseline BMI: below 20 kg/m2 (7.5%), 20 to 25 kg/m2 (47.0%), 25 to 30 kg/m2 (34.5%), and 30  kg/m2 or higher (11.0%).

The researchers performed Cox regression analyses to calculate hazard ratios associated with BMI groups, using normal BMI (20 to 25 kg/m2) in the younger patients as the reference category.

For the younger dialysis patients, compared with those in the normal BMI group, the adjusted hazard ratios by BMI category were 2.16 (1.37 - 3.40), 1.00 (reference category), 0.89 (0.65 - 1.23), and 1.60 (1.11 - 2.30), respectively. For the older dialysis patients, the hazard ratios were 1.64 (1.03 - 2.63), 1.18 (0.84 - 1.66), 1.18 (0.84 - 1.65), and 1.06 (0.71 - 1.59), respectively.

"The common belief may be that the obesity paradox holds true for all dialysis patients, but we are the first to show that it is not associated with elderly patients," Dr. Hoogeveen said.

"We don't really know the reason, but one possible explanation is that it takes time to die from obesity — at least 7 years — and the elderly dialysis patients who died within 7 years likely died from other causes, so they didn't have time to die from obesity," she proposed.

Frank C. Brosius, MD, professor of internal medicine at the University of Michigan Department of Molecular and Integrative Physiology in Ann Arbor and session moderator, agreed that the obesity paradox continues to be somewhat baffling, and although the study adds a new dimension to the trend, many questions remain.

"It has never been clear why there was a trend for obese patients to do better on dialysis than normal-weight patients," said Dr. Brosius. "It has been speculated that only the very hearty obese patients survived to reach dialysis or that the better nutritional status of obese patients allowed them to withstand more illness, but there has never been a clear explanation."

"The study in question found that this paradoxical effect does not seem to exist in younger patients, who tend to do better if [they are of] normal weight and not at either extreme," he added.

"Why more elderly patients have the paradoxical survival trends is not clarified by this study, unfortunately, so we are left speculating again," Dr. Brosius said.

"The response in the younger patients is as predicted — it's the older ones that are the odd ducks."

Dr. Hoogeveen and Dr. Brosius have disclosed no relevant financial relationships.

Renal Week 2010: American Society of Nephrology 43rd Annual Meeting. Abstract TH-PO487. Presented November 18, 2010.


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