N-Acetyl-l-cysteine is an amino acid that has antioxidant properties to support heart health, protect your cells from free radicals and promote overall well-being. NAC may support the functioning of your respiratory system. Since it contains sulfur, NAC may thin the mucus by weakening the disulfide bonds. As a result, you can expel the mucus from your upper respiratory tract more easily, which will help you feel better, especially because mucus also traps bacteria and other particles. NAC also serves as a precursor to glutathione, which promotes increased production of the antioxidant; this may be helpful as your age. A NAC supplement may boost the level of glutathione present in your tissues, which can boost immunity and make you less likely to get sick. Glutathione supports the proper functioning of lymphocytes, which are immune system components. It can also promote heavy metal detoxification.