18 Hidden Causes of High Neutrophil Counts That Doctors Want You to Know

14. Extreme Exercise and Overtraining

While regular exercise is widely recognized as beneficial for immune function, excessive physical exertion—especially among elite athletes or individuals engaging in extreme endurance training—can actually trigger neutrophilia. When the body undergoes intense physical stress, muscle fibers experience microscopic damage, and the immune system responds by increasing neutrophil production to aid in tissue repair. This effect is particularly pronounced in marathon runners, triathletes, and those who engage in prolonged high-intensity workouts. Additionally, overtraining without adequate recovery can lead to chronic inflammation, keeping neutrophil levels elevated for extended periods. While exercise-induced neutrophilia is usually temporary and not harmful, persistent overtraining without proper rest can compromise immune function, making individuals more susceptible to infections and fatigue. Balancing high-intensity training with proper recovery periods is key to maintaining a healthy immune response.