Caffeine is a part of the breakfast meal of many Americans. Many also take a multivitamin supplement daily as a part of their morning routine. Not many people are aware that taking vitamins at the same time as a cup of coffee or tea can interfere with the body's absorption of many necessary nutrients.
Caffeine causes calcium to be excreted in the urine and feces. For every 150 mg of caffeine ingested, about the amount in one cup of coffee, 5 mg of calcium is lost. This effect occurs even hours after the consumption of caffeine. One study of postmenopausal women found that those who consumed more than 300 mg of caffeine lost more bone in the spine than women who consumed less.
Caffeine also inhibits the amount of calcium that is absorbed through the intestinal tract and depletes the amount retained by the bones. Studies have shown that women with high caffeine intake suffer more hip fractures than those who avoid caffeine or drink in moderation (1 to 2 cups per day).
Caffeine inhibits vitamin D receptors, which limit the amount that will be absorbed. Because vitamin D is important in the absorption and use of calcium in building bone, this could also decrease bone mineral density, resulting in an increased risk for osteoporosis.
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.
Caffeine has a mild diuretic effect, which increases urination. Water soluble vitamins, such as the B-vitamins, can be depleted as a result of the fluid loss. In addition, it interferes with the metabolism of some B-vitamins, such as thiamine (vitamin B1). The one exception to this rule appears to be vitamin B12. Caffeine stimulates the production of stomach acid, which actually helps the body absorb B12.
Other Vitamins and Minerals
Caffeine may reduce the absorption of manganese, zinc and copper. It also increases the excretion of the minerals magnesium, potassium, sodium and phosphate. There is also evidence that caffeine interferes with the action of vitamin A.
Sources of Caffeine
Coffee and tea are obvious sources of caffeine. Even decaffeinated versions contain a little residual caffeine. Other sources include soft drinks, chocolate, cocoa and some energy drinks. Some supplements and medications, such as those that promote wakefulness, along with pain relievers for headaches, contain caffeine anhydrous, which is the dried, powdery form of caffeine. Dietary supplements sometimes use a natural ingredient called guarana, which is another form of caffeine.
A cup of coffee or green tea a day is not likely to have a negative effect on your overall health. However, in excess, caffeine can cause nutrient deficiencies that can affect both health and quality of life. As with most dietary factors, moderation and balance are key in optimal nutrition intake.