The immune system is a complex network of cells, tissues and organs. It protects the body from disease by fighting disease-causing germs and eliminating foreign substances. A weak or overactive immune system can lead to various health problems such as allergies, infections or autoimmune diseases. Natural dietary supplements can support and strengthen the immune system - for example by supplying vitamin C or probiotic bacterial strains to promote a healthy intestinal flora. A balanced diet and regular exercise also help to keep the immune system in top shape.