Sales of unnecessary products is simply a consequence of capitalism working properly. People create needs that didn't exist previously through marketing which is all most "health" advice on television (eg Dr Oz) or other media is. Legitimate nutritional deficiencies and cherry picked studies help fuel the marketing strategy. They get fantastic viral social media support from all the hypochondriacs, paranoid conspiracists and other health nuts who can't think critically and lack the scientific education to assess the marketing.

Some vitamins and vitamin analoques do have legitimate benefits as medication but best leave the dosing to a qualified health professional. Much better to eat a balanced diet with lots of vegetables, fruit and some whole protein. And get some sun in moderation if the climate supports it.