Taking vitamins with certain beverages can reduce absorption efficiency. Tannins and caffeine in many tea varieties interfere with your body’s ability to absorb some vitamins and minerals, especially iron. Herbal teas, on the other hand, actually enhance absorption. In addition, taking vitamins together with other supplements, such as iron, is not always efficient as some nutrients need fatty foods in your stomach and intestines to be properly absorbed.
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In general, three main tea categories exist: black teas, green teas and herbal teas. Black teas, such as Earl Grey and English Breakfast, are commonly consumed throughout the world and contain the most tannins and caffeine of the tea types, according to David Hoffman, author of “Medical Herbalism." Tannins are compounds that make black teas and red wines taste astringent and slightly bitter. Green teas are more commonly consumed in Asian countries, but also by Americans who are interested in different tastes and the antioxidant and fat-burning properties of green tea. Green tea contains virtually no tannins and lesser amounts of caffeine compared to black teas, although brewing methods greatly affect caffeine content. Herbal infusions, such as chamomile, are often referred to as teas and usually don’t contain any tannins or caffeine.
Affect of Caffeine
Caffeine inhibits vitamin D receptors within your body, which limits the amount absorbed when you take supplemental forms, according to the book “Metabolic Regulation: A Human Perspective” by Keith Frayn. Reduced vitamin D levels affect the absorption and use of calcium in building strong bones. Caffeine displays diuretic effects, which causes you to urinate more frequently. Increased rates of urination and fluid loss can reduce the concentrations of water-soluble vitamins such as the B-complex vitamins and vitamin C. Further, caffeine interferes with the metabolism of vitamin B1, or thiamine. However, caffeine stimulates the production of stomach acid, which can help your body absorb vitamin B12. For iron, caffeine significantly reduces its absorption rates in your intestines, by up to 80 percent, according to “Medical Biochemistry: Human Metabolism in Health and Disease.”
Affect of Tannins
Tannins don’t seem to affect the absorption of vitamins, but they do bind to iron and block its absorption in your intestines, as cited in the book “Nutrition and Wound Healing” by Joseph Molnar. Iron deficiency leads to anemia and symptoms of fatigue, dizziness and reduced metabolism, among others. In addition to caffeine and tannins, other dietary items that interfere with iron absorption include eggs, milk, cheese and bran. Consult with your doctor about whether you need to supplement with iron.
Taking vitamin and iron supplements with black and green teas is best avoided and you should wait at least an hour to take any supplements if you are a tea or coffee drinker. Some herbal teas, such as rose hip tea, actually enhance the absorption of iron because of its high vitamin C content. Herbal teas are also ideal for nighttime consumption because of their lack of caffeine and mild sedative properties, especially chamomile and valerian root teas.