Background: Allostatic Load is a construct used to quantify the cumulative burden of exposure to stressors that, over the course of an individual's life, exert a toll on the body's physiological functions, increasing risks of various chronic ailments and conditions. Studies attempting to quantify allostatic load have used a variety of clinical biomarkers representing primary and secondary mediators. In this study, we demonstrate the value of including red blood cell distribution width (RDW) among the panel of clinical parameters used to calculate allostatic load. Methods: We develop a novel formulation of allostatic load using RDW and other standard biomarkers. This index is computed using clinical laboratory data from the NHANES study. The predictive validity of the new index for tertiary outcomes (all-cause mortality and physician-assessed health status) is compared to that of the current formulation using Harrell's C index, ROC analysis and regression-based goodness-of-fit measures. Results: Inclusion of RDW as an allostatic load biomarker yields a significantly improved index. It demonstrates a superior ability to predict mortality, health status and biological age than the standard formulation currently in use. Conclusion: RDW has shown strong correlations with mortality and a broad spectrum of diseases. A review of the existing literature on allostatic load reveals its underutilization in this area, despite being a standard component of blood count panels. This study is the first to demonstrate its usefulness as a potential allostatic load biomarker.