Journal Title (Medline/Pubmed accepted abbreviation): Br. J. Nutr.
Page numbers: 588-595
Background: Caffeine is consumed by a large proportion of adults. Also, it has a reputation to accelerate dehydration because of its purported diuretic effects. However, it is not known if “normal” ingestion of caffeinated black tea accelerates dehydration. Tea contains many additional compounds (flavonoids, guanine, etc.) and the amount of caffeine is less than in caffeine pills, which have traditionally been used in hydration studies.
Hypothesis: Black tea will not have an effect on blood or urine measurements of hydration at the concentrations studied.
Subjects: Males, age 20-54 y (average 36). There were 19 men who finished the study.
Experimental design: randomized, cross-over
Treatments: Black tea was prepared fresh with semi-skimmed milk, no sweetener. Boiled water was used as a control. There were 4 treatments (consumed throughout the day):
- Four mugs of tea (168 mg caffeine)
- Six mugs of tea (252 mg caffeine)
- Four mugs of water
- Six mugs of water
The participants reported to the laboratory after an overnight fast. A baseline blood draw was acquired and then they ingested one serving of the test beverage. Additional servings of the beverage were offered at 2, 6, and 10 hrs for the four-cup protocol and 2, 4, 6, 8, and 10 hrs for the six-cup protocol. The participants remained at rest in the laboratory for the whole duration of the study and received standardized meals. Blood samples were acquired at 6 points throughout the day. Urine was collected for 24 hrs starting when they arrived at the laboratory and assessed for color. At least 5 days separated laboratory visits.
Normal tea consumption probably does not cause dehydration. British nutritional advisory committees recommend consuming extra water when consuming caffeinated beverages, but this practice may not be warranted.
These participants rested the whole day indoors. These results should not be translated to highly active days.