Dried powdered fruit and vegetable supplements, multivitamins, and other health remedies, even garlic and vitamin C or E, may show some benefits in those with deficient or marginal intake of antioxidants and phytochemicals, but the best and most effective way to prevent illness is with comprehensive nutritional adequacy maintained all year with dietary and supplemental recommendations, not by looking for specific cold remedies.
Almost every family has their favored remedies and advice. From chicken soup to wearing cloves of garlic around the neck to wearing warm hats, your mother learned her immunity-enhancing ideas from her mother. Unfortunately, chicken soup, steam vaporizers, hot tea with honey, and rubbing smelly salves on the chest do not have scientific data to document effectiveness and in fact, have mostly been debunked in scientific investigations. In fact, when scrutinized with high-quality placebo trials, almost all remedies show no significant effects, unless a person was somewhat nutritionally deficient before supplying more of the needed micronutrients. For example, pomegranate is a superfood that builds stronger immune function, and the long-term use of it and other highly nutritious superfoods may decrease the incidence of infections, but they should not be seen as cold remedies, but merely a highly nutritious food that supports a normal functioning immune system, which enhances immunity.
Even vitamin D, elderberry, and zinc, which have proven efficacy, are likely only of value in people whose levels are suboptimal. So the goal is still to achieve nutritional adequacy and forgets the idea of nutritional remedies when ill. Take 15 mg of zinc per day all year, and increase to 30 mg with an onset of cold symptoms. Probiotics and elderberry syrup are likely worth a try when ill.