Abstract Body (Do not enter title and authors here): Background: Chronic hypohydration and heightened adiposity are established contributors to CVD risk that are modified by lifestyle behaviours. However, traditional monitoring methods require specialised equipment and are impractical for everyday use. Emerging wrist-worn devices with body impedance analysis (BIA) capabilities offer a non-invasive solution for monitoring body composition to aid in CVD risk self-management. Aims: To validate the accuracy of a wrist-worn BIA device and associated algorithms in measuring body fat percentage (BFP) and total body water (TBW) relative to gold standard measurements. Methods: This cross-sectional, single-centre study recruited healthy participants with diverse demographic and anthropometric characteristics for a single time-point investigation at the Human Interventions Studies Unit, Ulster University. Two-minute BIA recordings were collected from participants on a proprietary wrist-worn device and used to train and validate a predictive BIA algorithm. BFP and TBW metrics were validated against clinical-grade measurements on a GE Lunar DEXA scanner and Impedimed SFB7 device, respectively. Algorithm accuracy was evaluated using the mean absolute error (MAE) between predicted and true values. The R² value assessed the predictive model's goodness of fit. Results: A total of 130 participants were recruited (44% male, 82% Caucasian, mean age: 39.8±14.8 years, mean BMI: 25.4±5.5 kg/m²; Figure 1a), 15 of whom were excluded for failing to adhere to the study protocol. The remaining 115 subjects’ data were divided into training (n=100) and test (n=15) sets. On test data, regression analysis indicated a strong relationship between algorithm-predicted values and true values of BFP (R²=0.83; Figure 1b) and TBW (R²=0.83; Figure 1c). The algorithm accurately measured BFP and TBW, achieving a MAE of 3.4% for BFP and 2.3 L for TBW relative to gold standard measurements. Conclusion: The wrist-worn BIA technology has shown comparable accuracy to gold standard devices in measuring BFP and TBW. These findings suggest that wearable BIA devices could serve as effective, non-invasive tools for body composition monitoring, enabling individuals to better manage their cardiovascular health.