We all know that vitamin C is the poster child immune booster. But there’s something else you should actually be grabbing when you feel that pesky cold coming on: probiotics. Why?Because your immune system starts in your gut. Yup, your gut health and your immune system are tied together like two peas in a pod against sickness. “A huge proportion of your immune system is actually in your GI tract,” says Dan Peterson, assistant professor of pathology at the Johns Hopkins University School of Medicine. While bacteria get a bad rap, the good kind of bacteria is something you need to keep your gut in balance for an overall-healthier you.