To strengthen your immune system, add a daily dose of probiotics to your arsenal of supplements. That’s what researchers concluded from a recent study at the Institute for Physiology and Biochemistry of Nutrition in Germany. Participants in the study who took supplemental probiotics daily for at least three months shortened bouts of the common cold by almost two days and reduced the severity of symptoms such as headaches, coughing, and sneezing (Clinical Nutrition, 2005, vol. 24, no. 4).

“Probiotics are not just good for the gut, they are also a good immune stimulator,” says Hilary Andrews, ND, an adjunct professor at the National College of Naturopathic Medicine in Portland, Oregon. “The bacteria in probiotics strengthen the immune system by providing it with extra stimulation, and then when we are exposed to viruses or harmful bacteria, the immune system is strong enough to handle them quickly and effectively.”

Be careful when choosing a brand, Andrews adds, because not all probiotics are created equal. Look for supplements that contain live, natural bacteria. Andrews advises buying a recommended brand from a natural products store you trust and taking roughly 12 billion colony-forming units (CFU) per day. It’s also a good idea to rotate brands, she says, so the body can benefit from a variety of helpful bacteria strains.