Black tea

Black Tea/Nutrient Depletion:

  • General (vitamins and minerals)General (vitamins and minerals): According to secondary information, caffeine consumption may result in a loss of several vitamins and minerals, including thiamine (B1), riboflavin (B2), pyridoxine (B6), vitamin B, vitamin C, potassium, magnesium, zinc, and iron.
  • CalciumCalcium: Theoretically, caffeine can increase urinary calcium levels (112). Experts report that tea polyphenols do not interfere with the bioavailability of calcium (276; 111). Additionally, a 1994 NIH advisory panel concluded that caffeine has not been found to affect calcium absorption or excretion significantly and that two tablespoons of milk added to one cup of coffee can counteract any of the calcium lost.
  • FolateFolate: In human research, both green and black teas reduced folate bioavailability (85).
  • GlucoseGlucose: Caffeine consumption has resulted in an increase and decrease in glucose (384). In human research, black tea decreased postprandial plasma glucose (390).
  • IronIron: Caffeine may inhibit iron absorption, which can lead to iron deficiency anemia. In thalassemia major and intermedia patients, tea caused inhibition of iron absorption (337). Impaired iron metabolism and microcytic anemia may occur in infants of breastfeeding women consuming caffeine (101). Experts report that tea polyphenols may inhibit iron absorption by binding to iron in the gastrointestinal tract and forming insoluble complexes. This binding appears specific to nonheme forms of iron only, with black tea demonstrating greater inhibition than green tea. Ascorbic acid may overcome this binding. Vegetarians are recommended to drink tea between meals, as binding by tea could exacerbate the low availability of iron found in plant sources (276). The effect of tea consumption on iron status has been investigated by various authors (338; 339; 340).
  • LipidsLipids: According to clinical review, meta-analysis, and animal research, caffeine may increase cholesterol and triglyceride levels (73; 88; 307; 396). Moderate (224mg) and high (674mg) tea catechins reduced postprandial triglyceride levels in healthy adults (397).
  • MagnesiumMagnesium: According to secondary sources, at high levels, caffeine may increase magnesium loss in urine.
  • PotassiumPotassium: According to clinical review and human reports, caffeine, particularly in large amounts, may reduce potassium levels (399; 400; 401).
  • ThiamineThiamine: Black tea may inhibit the body's utilization of thiamine (theoretically).