Lemons are rich in vitamin C and other antioxidants that can help boost the immune system against germs that cause colds and flu. Adding vitamin C from lemons will reduce the incidence of colds, they can help reduce the duration of colds.
Vitamin C can also help boost immunity in people who are undergoing extreme physical activity. Squeeze a lemon into a glass of hot water with a teaspoon of honey and you will have a soothing drink for people with coughs or colds.