This study aimed to examine the relationship between fibroblast growth factor 19 (FGF19) and depressive symptoms, measured by Beck’s Depression Inventory (BDI) scores and investigate the moderating role of smoking.

This study involved 156 Chinese adult males (78 smokers and 78 non-smokers) from September 2014 to January 2016. The severity of depressive symptoms was evaluated using the BDI scores. Spearman rank correlation analyses were used to investigate the relationship between cerebrospinal fluid (CSF) FGF19 levels and BDI scores. Additionally, moderation and simple slope analyses were applied to assess the moderating effect of smoking on the relationship between the two.

FGF19 levels were significantly associated with BDI scores across all participants (r = 0.26, p < 0.001). Smokers had higher CSF FGF19 levels and BDI scores compared to non-smokers (445.9 ± 272.7 pg/ml vs 229.6 ± 162.7 pg/ml, p < 0.001; 2.7 ± 3.0 vs 1.3 ± 2.4, p < 0.001). CSF FGF19 levels were positively associated with BDI scores in non-smokers (r = 0.27, p = 0.015), but no similar association was found among smokers (r = −0.11, p = 0.32). Linear regression revealed a positive correlation between FGF19 and BDI scores (β = 0.173, t = 2.161, 95% CI: 0.015–0.331, p < 0.05), which was negatively impacted by smoking (β = −0.873, t = −4.644, 95% CI: −1.244 to −0.501, p < 0.001).

These results highlight the potential role of FGF19 in individuals at risk for presence of or further development of depressive symptoms and underscore the importance of considering smoking status when examining this association.