Don't Take Vitamins with Your Coffee
Taking vitamins or mineral supplements with coffee can diminish their beneficial effects because caffeine blocks the absorption of vitamin D and iron.
Health consultants for the Chosun Ilbo said caffeine blocks the receptors in the small intestines that absorb vitamin D, and iron bonds easily with caffeine and ends up being secreted in urine without being absorbed.
Caffeine can decrease iron absorption by up to 80 percent.
Vitamin B and C are also affected by the diuretic response caused by caffeine. The body absorbs only necessary amounts of vitamins like B and C and releases the rest through urine, but caffeine increases the diuretic response, so more is lost.
Calcium and minerals should also be consumed without caffeine.
Since it takes about two hours for the body to get rid of caffeine, the best thing is to wait until then.