Is obesity associated with a survival advantage in patients starting peritoneal dialysis?

Obesity has been found to be associated with a survival advantage in hemodialysis patients. Results from studies in peritoneal dialysis (PD) patients are inconsistent. The aim of this paper was to study the association between obesity and mortality in the PD population in the Netherlands Co-operative Study on the Adequacy of Dialysis-2 (NECOSAD) cohort and critically discuss the observational data from an epidemiological perspective.

Patients starting PD were selected from the Netherlands Co-operative Study on the Adequacy of Dialysis-2 (NECOSAD), a prospective cohort study in incident dialysis patients in The Netherlands and followed for 5 years. Cox regression analysis was used to calculate relative risk of mortality (hazard ratios (HR) with 95% CIs) of baseline and time-dependent BMI, with a BMI of 18.5-25 as the reference.

In total, 688 patients with end-stage renal disease starting with PD were included (66% men, age: 53 +/- 15 years, BMI: 24.6 +/- 3.8 kg/m2). At the start of dialysis, 8.4% of the patients were obese (BMI > or =30). Compared with a normal BMI, obesity at the start of PD (BMI > or =30) was associated with a HR of 0.8 (0.5, 1.3). Time-dependently, this was 0.7 (0.4, 1.2). The HR of BMI < 18.5 at the start of PD was 1.3 (95% CI: 0.4, 3.2), and time-dependently this was 2.3 (1.0, 5.3).

Observational data suggest that PD patients who are obese at the start of dialysis do not have a worse survival compared with PD patients with a normal BMI. PD patients with a low BMI during dialysis have a twofold increased mortality risk. However, it can be argued to what extent the observed association between BMI and mortality in the dialysis population can be causally interpreted.