This study examines the differences in circulating levels of cytokines among Japanese in Japan (JJ), Japanese Americans (JA), and whites and their associations with obesity and marine n-3 fatty acids (FA) in a cross-sectional population-based study of 297 men aged 40-49 (100 JJ, 99 whites, and 98 JA). Experimental studies show that cytokines are associated with obesity positively and marine n-3 FA inversely. Serum interleukin-1α (IL-1α), IL-1 receptor agonist (IL-1ra), IL-4, IL-8, IL-10, inducible protein-10 (IP-10), tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and marine n-3 FA were determined. Body mass index (BMI), waist circumference, and computed tomography-measured visceral and subcutaneous adipose tissues were determined. The JJ had significantly lower levels of IL-1α, IL-4, IL-8, MCP-1, and TNF-α than whites and JA. Whites and JA had similar levels of IL-1α, IL-4, and IL-8 whereas whites had significantly higher levels of MCP-1 and TNF-α than JA. The JJ were least obese (BMI (kg/m2), mean-standard deviation) 23.6-2.8, 27.9-4.6, and 27.9-4.5 for JJ, whites, and JA, respectively. The JJ had marine n-3 FA about 100% higher than whites and JA (serum marine n-3 FA (%), median (interquartile range) 8.79 (7.41, 11.16), 3.47 (2.63, 4.83), and 4.44 (3.33, 6.01) for JJ, whites, and JA, respectively). Generally cytokines had weak and nonsignificant associations with indices of obesity and nonsignificant associations with marine n-3 FA. BMI had significant inverse associations with IL-1α, IL-4, and IL-8 in JA (P?<?0.05). Marine n-3 FA had marginally significant inverse associations with IL-8 in JJ (P?=?0.055) and TNF-α in whites (P?=?0.076). The JJ had lower levels of many cytokines than whites and JA. Generally cytokines had weak and nonsignificant associations with indices of obesity and marine n-3 FA. Further investigation is needed to determine why JJ had lower circulating levels of cytokines.
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