If one is taking vitamins and minerals every day, then on days where one feels a headache coming on, the ones in the wrong group should not be taken that day, since they would worsen the headache, or prevent the other group from being effective enough to relieve the headache. For the same reason it is usually better for a headache-prone person to take all daily supplements later in the day, as by then, most people will have had signs of an impending headache... Full Text