Zinc is a popular supplement for relieving common cold symptoms. Studies have found that zinc can help shorten the duration of a cold and reduce the number of upper respiratory infections in children. The mineral is required for the development and functioning of immune cells in the innate and the adaptive immune system.
Black elderberry (Sambucus nigra) extracts have been shown to reduce the severity and length of certain types of influenza. The berries and flowers of elderberry are packed with antioxidants, especially anthocyanins, as well as vitamins with immune boosting properties, such as vitamin C.
In one randomized study of 60 adults with flu-like symptoms, those who took 15 mL of the elderberry syrup four times a day saw symptoms clear up on average four days earlier than those who took a placebo syrup.
Another study tested its effectiveness in air travelers. Those who took the elderberry syrup had a shorter duration of cold symptoms that were less severe than the control group.