In the normal state, blood has no business anywhere except in the confines of the heart and blood vessels and in the sinusoids of the marrow, liver, and spleen. Of the average 5 L of blood, only 2.25 L, or 45%, consists of cells.
Take-away: Calcium and magnesium may best be taken in the evening with food or before nighttime sleep. Since zinc should not be taken with calcium and apart from iron, it is most useful if taken earlier in the day either slightly before/after food. Iron should ideally be taken on an empty stomach and separately from other multivitamin/multimineral combinations.
1 Preconception â Between the ages of 14 and 18 you need 9 milligrams of zinc a day. Between 19 and 50 years of age, you should get 8 milligrams of zinc a day.  Pregnancy â During pregnancy you need more zinc and should get 11 milligrams a day, 13 milligrams if you are 18 years old or younger.