This funny-sounding nutrient is found in tons of foods and can help your system fend off sickness. With warm mugs of hot cocoa, fuzzy socks, and cozy fires of winter can also come stuffy noses, colds, and the flu. Thankfully, there are so many ways we can boost our immune systems, through everyday habits and choices—regular exercise, adequate sleep, and the healing power of food and nutrition. Enter: quercetin, a plant compound found in a variety of familiar foods that will help your immune system thrive, ward off cold and flu, and also improve your overall health. When it comes to determining what makes a food healthy, many turn to…