Obesity and mortality risk among younger dialysis patients

Abstract

Background and objectives: Many studies show that obesity in dialysis patients is not strongly associated with mortality but not whether this modest association is constant over age. This study investigated the extent to which the relation of body mass index (BMI) and mortality differs between younger and older dialysis patients.

Design, setting, participants, & measurements: Adult dialysis patients were prospectively followed from their first dialysis treatment for 7 years or until death or transplantation. Patients were stratified by age (<65 or ≥65 years) and baseline BMI (<20, 20-24 [reference], 25-29, and ≥30 kg/m(2)).

Results: The study sample included 984 patients younger than 65 years and 765 patients 65 years or older; cumulative survival proportions at end of follow-up were 50% and 16%. Age-standardized mortality rate was 1.7 times higher in obese younger patients than those with normal BMI, corresponding to an excess rate of 5.2 deaths/100 patient-years. Mortality rates were almost equal between obese older patients and those with normal BMI. Excess rates of younger and older patients with low compared with normal BMI were 8.7 and 1.1 deaths/100 patient-years. After adjustment for age, sex, smoking, comorbidity, and treatment modality, hazard ratios by increasing BMI were 2.00, 1, 0.95, and 1.57 for younger patients and 1.07, 1, 0.88, and 0.91 for older patients, implying that obesity is a 1.7-fold (95% confidence interval, 1.1- to 2.9-fold) stronger risk factor in younger than older patients.

Conclusions: In contrast to older dialysis patients, younger patients with low or very high BMI had a substantially elevated risk for death.

Figure 1.

Crude and age-standardized mortality rates by body mass index (BMI) category. Crude and age-standardized mortality rates (per 100 person-years) with 95% confidence intervals in four categories of baseline BMI during 7 years of follow-up of dialysis patients younger than 65 years and older than 65 years. py, patient-years.

Figure 2.

Relation between body mass index (BMI) and mortality rates within age quartiles. Hazard ratios for mortality depending on BMI were modeled by separate restricted cubic splines within age quartiles in a Cox regression model. Patients with extreme values of BMI (<18 kg/m² [2%] and >40 kg/m² [0.4%]) were excluded from the figure. The reference was a BMI of 25 kg/m². The model was adjusted for age, sex, product term between age and BMI, smoking, comorbidity (history of cardiovascular disease, chronic lung disease, and malignancy), and treatment modality (hemodialysis or peritoneal dialysis).

Figure 3.

Relation between body mass index (BMI) and mortality rates with 95% confidence intervals (dotted curves) for younger (<65 years) and older (≥65 years) dialysis patients. Hazard ratios for mortality depending on BMI were modeled by separate restricted cubic splines for younger (<65 years) and older (≥65 years) dialysis patients in a Cox regression model. Patients with extreme values of BMI (<18 kg/m² [2%] and >40 kg/m² [0.4%]) were excluded from the figure. The reference was a BMI of 25 kg/m². The model was adjusted for age, sex, smoking, comorbidity (history of cardiovascular disease, chronic lung disease, and malignancy), treatment modality (hemodialysis or peritoneal dialysis), and product term between age and BMI.