Many people take their daily vitamins or iron-containing supplements right after their breakfast with a cup of tea or coffee. The question is: Is that the optimum way to consume your supplements? Probably not, as research shows that caffeine interferes with the body’s absorption of iron, which is necessary for red blood cell production. Drinking caffeine at the same time as an iron source can reduce absorption by up to 80%, according to the Nutrition Desk Reference. Any beverage containing caffeine should be separated from iron-containing foods or supplements by at least one hour.