透析患者のBMIと死亡率：メタ解析

人工透析患者のBMIと死亡率の関係を調査したメタ解析を紹介します。

Wang Jialin, Zhou Yi, Yuan Weijie. Relationship between Body Mass Index and Mortality in Hemodialysis Patients: A Meta-Analysis. Nephron Clin Pract 2012;121:c102-c111 (DOI: 10.1159/000345159)

リサーチクエスチョンは以下の通りです。

P：人工透析患者で
E：BMIが高いと
C：BMIが正常の場合と比較して
O：死亡率が低い
D：メタ解析

結果ですが、4研究、81423人のデータを統合すると、BMIが高値でない場合ち比較して、BMI25以上の場合には死亡率が有意に低かったです。人工透析患者では、肥満パラドックスが成立するという結論です。

悪液質の原因疾患では、肥満パラドックスが報告されています。ただ、筋肉量が十分ある肥満なのか、サルコペニア肥満なのかで、死亡率が異なる可能性もあります。今後はBMIだけでなく、筋肉量や脂肪量が死亡率と関連するかを知りたいですね。

Abstract
Background: Previous studies have reported that reduced mortality rates in hemodialysis (HD) patients were negatively related to body mass index (BMI). The potentially protective effect of increased BMI in HD patients has been referred to as ‘reverse epidemiology’. Our meta-analysis was conducted to examine the relationship between different BMI ranges and mortality in HD patients.

Methods: Eligible studies assessing the effects of BMI ranges on all-cause mortality (published from 1966 to February 2012) were searched, using ‘hemodialysis’ or ‘haemodialysis’ and ‘obese’ or ‘body mass index’ or ‘overweight’ as key words, in combination with ‘mortality’, ‘survival’, ‘reverse epidemiology’ and ‘obesity paradox’. Inclusion criteria were that trials reported mortality in HD patients according to the traditional World Health Organization/National Institutes of Health BMI classification, and BMI levels are acceptable within 2 index points. The quality of the trials was evaluated using the risk of bias assessment in studies included in Cochrane reviews. The mortality rates in HD patients were the primary end point of the study. With no significant heterogeneity, a fixed-effects model was used for analyses.

Results: Four studies with a total of 81,423 patients met final inclusion criteria. Compared to individuals with non-elevated BMI, those with elevated BMI (BMI ≥25, OR 0.67, 95% CI 0.65–0.68) had a lower all-cause mortality. In a risk-adjusted sensitivity analysis, elevated BMI levels (adjusted hazard ratio 0.94, 95% CI 0.92–0.96) remained protective against mortality.

Conclusion: High BMI levels were associated with lower all-cause mortality rates in HD patients. It is possible that more stable hemodynamic status, cytokine and neurohormonal alternations contribute to the protective effects of BMI on mortality in HD patients. There is a need for prospective studies to elucidate mechanisms behind this relationship.