You can eat a proper amount of daily food and probably get 100iu of Vitamin D for example (just an example). People go to the rip off toxic supplement store and purchase 10,000iu of Vitamin D and think GREAAAAAT. What these people don't realise is that the amount in the food was virtually all assimilated and worked out at higher concentrations in the body. You see supplements are non natural and hardly get assimilated.