Personally, I do my best to stay away from medicine, I want my immune system to be strong when I get older so I don't necessarily have to take a lot of medicine.
Eat a lot of fruit. Oranges, apples, bananas.. those usually boost your vitamin levels up. Eat healthy food--salads, chicken breast, broccoli, things like that help.
Just stay healthy and active, and you'll be fine in no time