**Background:** The use of synthetic data in healthcare research is gaining interest as a way to increase data access and overcome privacy concerns. However, evidence that synthetic data can adequately train algorithms for use on real data is still limited. This study aimed to compare the performance of machine learning models trained on real versus synthetic data for predicting blood pressure from simple clinical variables.
**Methods:** Data were obtained from the National Diet and Nutrition Survey (NDNS) Rolling Programme (2008–2019). After exclusions (age <18 or >70, taking anti-hypertensives), 2832 participants remained. The dataset was split into training (85%, n=2408) and testing (15%, n=424). Eleven variables (age, sex, ethnicity, marital status, smoking status, socioeconomic status, total weekly screen time, frequency of takeaway meals, average nightly sleep duration, height, weight) were considered. Recursive feature elimination with tenfold cross-validation identified the optimal subset: age, sex, weight, and height. Missing data were imputed using the missForest package. Three model types were built using the caret package in R: Bayesian generalized linear regression (bayesglm), random forest (rf), and neural network (nn). Synthetic datasets were generated using the synthpop library: synthetic dataset A (n=2408), synthetic dataset B (n=4816), and a combined real+synthetic dataset (n=4816). All models were tested on the same real test set (n=424). Model performance was assessed using root mean squared error (RMSE), R-squared, mean absolute error (MAE), and residuals compared via Wilcoxon signed rank test.
**Key Results:** Synthetic datasets showed high fidelity with the real training data (propensity score mean-squared error values low; e.g., for age: pMSE=0.000225, S_pMSE=2.16 for synthetic A; pMSE=0.000011, S_pMSE=0.27 for synthetic B). Model performances were comparable across all training data types. For Bayesian linear regression: MAE ranged from 8.25 to 8.28; RMSE 10.45–10.47; R-squared 0.22. For neural network: MAE 8.12–8.19; RMSE 10.31–10.36; R-squared 0.24–0.25. For random forest: MAE 8.20–8.33; RMSE 10.49–10.71; R-squared 0.18–0.22. None of the Wilcoxon signed rank test p-values were <0.05, indicating no significant difference in residuals between models trained on real vs. synthetic data.
**Clinical Implications:** This study demonstrates that synthetic data can produce machine learning models with predictive accuracy equivalent to those trained on real data for estimating blood pressure using only age, sex, weight, and height. The minimalistic variable set enhances real-world applicability. However, the study used a non-representative sample and did not assess reidentification risk. Further research is needed to confirm generalizability and privacy protection before synthetic data can replace real patient data in clinical prediction modeling.