why people say an apple a day keeps doctors away?

Eating an apple gives energy to  every parts in our body.prevents many chronic diseases.we know prevention is better than cure.so eat an apple regularly keeps your health fresh.
uses of eating an apple 
brain: good for brain.
           prevents alzeimer disease.
eyes:   prevents cataract.
heart:  controls high blood pressure.
           good for heart.
           reduce bad cholestrol.
 lungs: controls asthama.
            cures lung infections.
 skin :  improves complexion.
 hair:helpful for hair growth
 total body: boots immune system.
                  prevents cancer.
                  fights free radicals
                  best food for weight loss.
                  controls constipation
 digestive system:controls diabetics.
                           boosts immune system.
                           prevents gall stones.
                           best food for anemic patients.
bones and teeth:gives strength to bones and teeth.