Apparently healthy adults with high serum gamma-glutamyl transferase levels are at increased risk of asthma development in the near future: a Korean nationwide cohort study.

Serum gamma-glutamyl transferase (GGT), an indicator of oxidative stress and/or a chronic inflammatory process, is associated with the levels of leukotrienes and other inflammatory mediators that play a critical role in the pathogenesis of asthma. This study aimed at investigating whether apparently healthy subjects with higher serum GGT levels at a national health check-up are at an increased risk of developing asthma in the near future.We analyzed 564,213 Korean adults, aged 20-80 years who underwent a national general health examination, including measurement of baseline serum GGT between 2003 and 2015, using data from a large-scale representative cohort of the Korean population. Data were analyzed using a Cox proportional hazards regression analysis.In total, 516,956 participants were included in the final analysis. During the mean follow-up period of 8 years (standard deviation, 4.0), 7,439 incident asthma events occurred. We then classified the male and female participants according to quartiles of blood GGT levels (males: ≤ 20, 21-30, 31-51, and ≥ 52 IU/L; females: ≤ 12, 13-16, 17-22, and ≥ 23 IU/L, respectively). The adjusted hazard ratio (aHR) for incident asthma was significantly greater for subjects in the highest GGT quartile than for those in the lowest GGT quartile (aHR, 1.47; 95% confidence intervals, 1.36-1.59). Further, there was a significant linear trend across quartiles with regard to asthma (ptrend<0.001). We estimated the optimal cut-off values (using the minimum p-value approach) as 35 IU/L for the total population, 35 IU/L for males, and 36 IU/L for females, respectively.Clinicians should be aware of the risk of incident asthma in healthy subjects with elevated GGT levels. Our findings advance our understanding of asthma pathogenesis.