I have been thinking about this as well. Particularly from the perspective of people (like my MIL) who eat an appalling diet, who smoke A LOT everyday and yet still seem to have no health problems, and live to a ripe old age.
My MIL gives me so much grief about trying to eat healthy and look after myself. She does no exercise. She smokes - constantly. She eats nothing but rubbish food. And she is a healthy 76 years old.
And she believes that vitamins will make you sick and kill you.