Your immune system works best to protect you from illness when it isn’t overloaded with toxins and stressors. However, if you have a demanding job, family responsibilities, and live in a large city, your immune system can be compromised, making you more susceptible to infections. Processed food, sugar, and smoking can also damage your immune system. Regular exercise, adequate sleep, and relaxation are all important to reducing stress and keeping your immune system strong. In addition, certain supplements containing plant sterols can help regulate your immune system and protect you from infections such as colds and flu.