Urologic cancers, prostate cancer (PCa), bladder cancer (BCa), and renal cell carcinoma (RCC), are associated with high morbidity and mortality. While monounsaturated fatty acids (MUFAs) have shown potential health benefits, dietary assessments are prone to confounding and measurement errors. This study used Mendelian randomization (MR) to explore the causal relations between MUFA intake and the risk of these cancers.

A two-sample MR analysis was conducted using genetic variants as proxies for MUFA intake. Outcome data were obtained from the FinnGen project (PCa: 17,258 cases, 143,624 controls; BCa: 1,701 cases, 258,704 controls; RCC: 2,223 cases, 287,137 controls). MR-PRESSO and MR-Egger tests were used to ensure the absence of pleiotropy. MR analysis was performed using the Inverse Variance Weighted (IVW) method, accompanied by sensitivity analyses to evaluate causal relations. Findings for PCa were further validated using PRACTICAL consortium data (79,148 cases, 61,106 controls).

MUFA intake was inversely associated with PCa risk (adjusted odds ratio [aOR] = 0.87, 95% confidence interval [CI]: 0.77–0.98, p = 0.028), and the relation persisted in validation analysis (aOR = 0.88, 95% CI: 0.79–0.98, p = 0.020). No associations were identified between MUFA and RCC (aOR = 0.99, 95% CI: 0.76–1.29, p = 0.924) or BCa (aOR = 0.94, 95% CI: 0.69–1.28, p = 0.696).

The results showed an inverse causal relation between MUFA intake and PCa; high MUFA intake has a protective effect against PCa. No associations were found for RCC or BCa.