Are vitamins good for you?

Nutrition: Vitamins on trial
After decades of study, researchers still can’t agree on whether nutritional supplements actually improve health.
Melinda Wenner Moyer
Nature 510, 462–464 (26 June 2014)
http://www.nature.com/news/nutrition-vitamins-on-trial-1.15459

But scientific opinion about the use of vitamin supplements by millions of seemingly healthy people has never been more divided.

“The tools we’ve had in the past have been so crude — it’s like we’ve been looking through a dirty window with the curtains closed,”

one of the many complexities of nutrient metabolism.
Nutrition scientists now recognize that risk curves are J- or U-shaped: nutrients have beneficial effects at low doses and toxic effects at high doses.
The magnitude of the response differs, too, depending on where individuals start on the curve — their baseline status.

Are supplements useless?
The current state of research offers only an equivocal half-answer: ‘maybe yes’ for some individuals, nutrients and doses, and ‘maybe no’ for others.
“Nutrition is complex, and I don’t think we’re necessarily going to find one formula that works for everybody,” says Mayne.

related article on within-cases analysis:
https://franzcalvo.wordpress.com/2014/06/29/gwas-explains-only-a-small-proportion-of-the-total-heritability