Vitamins and minerals – zinc and vitamin C were high on the list, and some herbs.
The brown-eyed redheads have slower reflexes and should consider getting more Vitamin X (or whatever it is).
For example, if the system (conspiracy theorists will call it "The System") determines that people like me are happier and healthier with more thiamine in their system, that will come up in my custom vitamin formulation, which also includes whatever nutrients I didn't get enough of that day.
Or, we gravitate toward anecdotes like, "I take my vitamin C every day and haven't had a cold in year."
For an example of this, consider the case of vitamin A deficiency (VAD).