Most of us know that lemons are healthful and chock full of vitamin C. Sailors used to take along lemons and limes on ocean voyages to protect them from diseases like scurvy. Today we know that one of the secret powerhouses of lemons and other citrus fruits is a substance called limonene. Limonene is a substance that the body uses to help protect cells from attack. Scientists are investigating the potential cancer-preventing properties of limonene.
Lemons are also antibacterial, that is, they kill certain kinds of germs. It’s one of the main reasons that lemon juice and water are recommended in cold and flu season. Travelers to cholera-prone areas are urged to add lemon or lime to all beverages as a disease preventative. In fact, in the ancient world, lemons were considered an antidote to many types of poisons.
Lemons also contain potassium which is one of the many chemicals that helps regulate proper heart function.
Grandma may have recommended tea with lemon, but scientists at Purdue have just found that combining green tea with lemon quadruples the healthful punch of green tea by helping the body utilize tea’s catechins. Catechins are substances that work like disease-fighting ninjas in the body—they are thought to fight cancer, prevent cardiovascular disease, lower cholesterol and other good things—but they are often unstable in the body. Green tea is loaded with catechins and the lemon helps make them stable, plus lemon adds some Vitamin C (an antioxidant powerhouse) to boot. The result is that green tea with lemon is a far more healthful drink than green tea or lemon juice alone.
 Crowell, PL (1999). “Prevention and therapy of cancer by dietary monoterpenes”. The Journal of nutrition 129 (3): 775S–778S. PMID 10082788. http://jn.nutrition.org/cgi/pmidlookup?view=long&pmid=10082788.