Background: Recent studies have revealed a close relationship between obesity and polymorphism in the inflammation gene. However, the association between interleukin-1beta (IL-1β) and obesity remains controversial. We therefore investigated the association between IL-1B C-31T polymorphism and obesity in Japanese. Methods: The participants were 802 inhabitants (281 men and 521 women) of Japan, aged 39 to 88 years, who attended a health examination in 2003. Body height, weight, waist and hip circumferences, and body fat percentage were measured. The IL-1B C-31T polymorphism was genotyped by polymerase chain reaction with confronting 2-pair primers. The association between IL-1B C-31T genotypes and various indices of obesity was then investigated. The confounding factor-adjusted odds ratios (OR) and 95% confidence intervals (CI) for obesity were calculated for each IL-1B C-31T genotype by using unconditional logistic regression analysis. Results: Among male carriers of the CT and TT genotypes, the ORs for high body fat percentage were 2.58 (95% CI, 1.17-6.34) and 2.81 (1.17-7.33), respectively, as compared to carriers of the CC genotype (P for trend = 0.037). Among women, carriers of the TT genotype had significantly higher ORs for high BMI (OR, 2.13; 95% CI, 1.25-3.67) and large waist circumference (2.49; 1.37-4.66), as compared to women with the CC genotype (P for trend = 0.005 and 0.004, respectively). Conclusions: The IL-1B C-31T polymorphism is associated with obesity in Japanese. Men and women with the TT genotype of IL-1B C-31T had a higher risk for obesity than those with the CC genotype.
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