Absence of Causal Relationship between Levels of Unsaturated Fatty Acids and ADHD: Evidence from Mendelian Randomization Study

Objective: Previous research suggests a potential link between unsaturated fatty acids (UFAs) and ADHD, but the causal relationship remains uncertain. This study aims to investigate the causal association between ADHD and UFAs using Mendelian randomization (MR) analysis. Methods: Summary data from genome-wide association studies were used to estimate the concentration of circulating UFAs, including Monounsaturated Fatty Acids (MUFAs), Polyunsaturated Fatty Acids (PUFAs), Omega-3 PUFAs, Omega-6 PUFAs, Linoleic Acid (LA), and Docosahexaenoic Acid (DHA). Data from the Psychiatric Genomics Consortium, including both childhood and adult ADHD, were respectively used to examine the relationship between genetically predicted UFAs levels and ADHD. Various MR methods, including Inverse-variance weighted (IVW), MR Pleiotropy RESidual Sum and Outlier, MR-Egger, weighted median, and weighted mode, were employed to assess heterogeneity and pleiotropy. Results: The IVW revealed only nominal evidence suggesting a potential causal relationship between genetically predicted PUFAs (OR = 0.92, 95% CI [0.85, 0.99], p = 0.031), Omega-6 PUFAs (OR = 0.90, 95% CI [0.83, 0.98], p = 0.020), and LA levels (OR = 0.90, 95% CI [0.82, 0.98], p = 0.021) with childhood ADHD risk. However, after false discovery rate correction, the p-values for PUFAs, Omega-6 PUFAs, and LA levels all exceeded the threshold for significance. For adult ADHD, we did not find any significant associations between the six circulating UFA levels and adult ADHD. Conclusion: Our findings do not support a causal relationship between UFAs levels and ADHD. This suggests that UFAs supplements may not be effective in improving ADHD symptoms and importantly, it appears that UFAs levels may not have a long-term effect on ADHD.