Physical Inactivity and Unhealthy Metabolic Status Are Associated with Decreased Natural Killer Cell Activity

PURPOSE: Several studies have reported relationships among physical activity, healthy metabolic status, and increased natural killer (NK) cell activity. However, large-scale data thereon are lacking. Thus, the present study aimed to assess NK cell activity according to physical activity and metabolic status. MATERIALS AND METHODS: A cross-sectional study was performed on 12014 asymptomatic examinees. Using a patented stimulatory cytokine, NK cell activity was quantitated by the amount of interferon-γ secreted into the plasma by NK cells. Physical activity levels were assessed using the validated Korean version of the International Physical Activity Questionnaire Short Form. RESULTS: The physically inactive group showed lower NK cell activity than the minimally active group (median, 1461 vs. 1592 pg/mL, p<0.001) and health-enhancing physically active group (median, 1461 vs. 1712 pg/mL, p=0.001). Compared to women with a body mass index (BMI) of 18.5–27.5 kg/m(2), those with a BMI <18.5 kg/m(2) had significantly lower NK cell activity (1356 vs. 1024 g/mL, p<0.001), and those with a BMI ≥27.5 kg/m(2) tended to have lower NK cell activity (1356 vs. 1119 g/mL, p=0.070). Subjects with high hemoglobin A1c levels and low high-density lipoprotein cholesterol levels, as well as men with high blood pressure and women with high triglyceride levels, exhibited lower NK cell activity. Moreover, physical inactivity and metabolic abnormalities were independently associated with low NK cell activity, even after adjusting for confounders. CONCLUSION: Physical inactivity and metabolic abnormalities are associated with reduced NK cell activity. Immune systems may become altered depending on physical activity and metabolic status.