Time at higher BMI linked to survival in peritoneal dialysis

A retrospective study of 670 adults receiving peritoneal dialysis found that spending more of the first three years of treatment with a body mass index between 26 and 30 kg/m² was associated with lower subsequent all-cause mortality. The result came from a time-in-range analysis at a single hospital in Ganzhou, China, and the researchers cautioned that the findings are exploratory rather than evidence for changing clinical targets. After a median follow-up of 2.3 years, 75 participants had died. Each 10-percentage-point increase in time spent in the 26–30 kg/m² range was associated with a 23% lower mortality hazard after adjustment for several demographic and clinical factors.

Most earlier investigations of the relationship between body mass index and outcomes in peritoneal dialysis have used BMI measured at enrollment or changes between two points. Those approaches cannot fully represent how long a patient remains at a given weight. The new study instead estimated the cumulative duration of BMI exposure at baseline, 12 months and 36 months. Its authors described time above a target range, or TAR, and time in a target range, or TTR, as longitudinal measures intended to capture sustained BMI rather than a single snapshot. The analysis used a landmark cohort design: the first three years defined the exposure period, and mortality was tracked only after participants reached the 36-month landmark.

The investigators scanned 15 integer BMI thresholds, from 18 to 32 kg/m², to identify the level most closely associated with lower mortality. Time above each threshold was calculated by Rosendaal linear interpolation. The lowest estimated hazard ratio occurred at 26 kg/m²: for each 10% increase in TAR above that threshold, the adjusted hazard ratio for death was 0.82, with a 95% confidence interval of 0.73 to 0.92 and a Bonferroni-corrected P value of 0.018. Although every threshold produced a point estimate below 1, only thresholds from 24 through 26 kg/m² remained statistically significant after correction for testing 15 cutoffs. The researchers therefore selected 26 kg/m² as the lower boundary of a candidate range and examined TTR in two prespecified intervals: 24–25.9 and 26–30 kg/m².

Participants entered the study if they were at least 18 years old, had received continuous ambulatory peritoneal dialysis for at least three months and attended a scheduled reassessment between January 2014 and December 2023. The investigators excluded 550 people, including two with missing baseline BMI, 287 with fewer than two BMI measurements during the first three years, 72 who died before the landmark, 75 who transferred to hemodialysis, 23 who received a kidney transplant, 18 who were lost to follow-up and 73 with other reasons for exiting before the landmark. The final group of 670 had a mean age of 48.2 years, and 54.5% were male. Its mean baseline BMI was 21.91 kg/m². Of these participants, 548 spent no time in the 26–30 kg/m² interval during the exposure period, while 122 spent at least some time there.

BMI was calculated from measured weight in kilograms divided by height in metres squared. Heights and weights were recorded by trained personnel using calibrated stadiometers and digital scales, with participants wearing light clothing and no shoes. The investigators used multiple imputation by chained equations to address missing data, generating 20 datasets and combining their estimates with Rubin’s rules. Survival models were fitted in stages: first without adjustment, then for age and diabetes, and finally for estimated glomerular filtration rate, serum albumin, high-density lipoprotein cholesterol, 24-hour urine volume and the cumulative number of peritonitis episodes during the 36-month exposure period. The fully adjusted model also included age and diabetes, making seven covariates in total. Post-hoc power for the primary TTR estimate was 63%.

The TTR results separated the two candidate intervals. Patients with any time in the 24–25.9 kg/m² range did not have a statistically significant association with mortality after full adjustment. The categorical hazard ratio for any versus no time in that lower range was 0.75, with a 95% confidence interval of 0.46 to 1.23, while the continuous hazard ratio per 10-percentage-point increase in TTR was 0.98, with a 95% confidence interval of 0.89 to 1.08. By contrast, any time in the 26–30 kg/m² range was associated with a hazard ratio of 0.27, with a 95% confidence interval of 0.11 to 0.68. For each 10% increase in TTR in that higher range, the adjusted hazard ratio was 0.77, with a 95% confidence interval of 0.62 to 0.96. A restricted cubic spline analysis found no evidence of non-linearity within the selected range, with a P value of 0.21 for non-linearity.

Sensitivity analyses broadly supported the main association. Complete-case analyses, recalculation of TTR with a step-function rather than linear interpolation, and Firth penalized Cox regression produced consistent results. In exploratory competing-risks analyses, each 10% increase in TTR within the 26–30 kg/m² range was associated with lower cardiovascular mortality, with a subdistribution hazard ratio of 0.68 and a 95% confidence interval of 0.53 to 0.88. The same exposure was not significantly associated with infection-related mortality; its subdistribution hazard ratio was 0.93, with a 95% confidence interval of 0.71 to 1.21. Those cause-specific analyses were underpowered and should not be treated as independent proof of a cardiovascular mechanism. The study also calculated E-values of 1.9 for the continuous association and 6.8 for the categorical comparison, estimating how strong an unmeasured confounder would need to be to explain each result.

Several potential explanations were discussed, but none was directly tested. A higher BMI could partly reflect greater nutritional reserve and muscle mass, potentially helping patients withstand protein-energy wasting, a common and dangerous complication of peritoneal dialysis. Other possibilities included metabolic effects of adipose tissue, inflammation and fluid status. BMI cannot distinguish fat, lean tissue and retained fluid, and the investigators had no direct body-composition or overhydration measurements. Twenty-four-hour urine volume served only as a partial adjustment for fluid status. Peritoneal transport status was also missing for roughly one-fifth of the cohort and was omitted from the primary model because the limited number of deaths constrained the number of supported covariates. The findings therefore cannot show that excess adiposity itself improved survival.

Important design limitations constrain the interpretation. The retrospective, single-center design cannot establish causality, and 75 deaths provided only 10.7 events per covariate and about 63% post-hoc power for the primary effect estimate. Survivor bias was possible because the landmark design excluded patients who died, transferred dialysis modality, received a transplant or otherwise left before 36 months; these exclusions may have selected relatively healthier survivors. Unmeasured confounding and measurement error also remain plausible, particularly because diet, physical activity, dialysis adequacy and medication data were unavailable. BMI was measured at only three time points, so interpolation may have missed short-term fluctuations. Exploratory subgroup and interaction analyses were underpowered and should not be used to identify patient subgroups. Larger multicenter cohorts with more frequent BMI measurements, validated body-composition data and adequate numbers of deaths are needed before the observed 26–30 kg/m² range can be considered a clinical target or generalized beyond this Chinese population.

Subject of Research: Longitudinal BMI time-in-range and mortality in adults receiving peritoneal dialysis

Article Title: The obesity paradox in peritoneal dialysis: reassessing optimal BMI via longitudinal time in range analysis in a single-center cohort

Article References: Wang, M., Zeng, X., Liu, D., Chen, P., & Peng, Z. (2026). The obesity paradox in peritoneal dialysis: reassessing optimal BMI via longitudinal time in range analysis in a single-center cohort. Frontiers in Nutrition, 13, 1982039. https://doi.org/10.3389/fnut.2026.1982039

Image Credits: AI Generated

DOI: 10.3389/fnut.2026.1982039

Keywords: peritoneal dialysis, body mass index, time in range, all-cause mortality, obesity paradox, retrospective cohort, Chinese patients, nutritional reserve, landmark analysis, obesity, paradox, peritoneal