High fish consumption may be associated with lower inflammation, suppressing atherosclerotic CVD (ASCVD). Long sleep duration, as well as short sleep, may contribute to inflammation, thus facilitating ASCVD. This study investigated the overall association between fish consumption, sleep duration and leucocytes count. We conducted a cross-sectional study between April 2019 and March 2020 with a cohort of 8947 apparently healthy participants with no history of ASCVD (average age, 46·9 ± 12·3 years and 59 % males). The average frequency of fish consumption and sleep duration were 2·13 ± 1·26 d/week and 6·0 ± 0·97 h/d. Multivariate linear regression analysis revealed that increased fish consumption was an independent determinant of sleep duration (β = 0·084, P < 0·0001). Additionally, habitual aerobic exercise (β = 0·059, P < 0·0001) or cigarette smoking (β = −0·051, P < 0·0001) and homoeostasis model assessment-insulin resistance (HOMA-IR) (β = −0·039, P = 0·01) were independent determinants of sleep duration. Furthermore, multivariate linear regression analysis identified fish consumption as an independent determinant of leucocytes count (β = −0·091, P < 0·0001). However, a significant U-shaped curve was found between leucocytes count and sleep duration, with 6–7 h of sleep as the low value (P = 0·015). Higher fish consumption may be associated with a lower leucocytes count in the presence of adequate sleep duration and healthy lifestyle behaviors. However, long sleep duration was also related to increased inflammation, even in populations with high fish consumption. Further studies are needed to clarify the causality between these factors.