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1. inTroducTion

1.1 thE ImPortAncE of ProPEr hydrAtIon for hEAlth

recently, the current knowledge of water intake as it pertains to human health was reviewed by Popkin et al (2010). this review highlights the importance of proper hydration for the prevention of nutrition-related diseases such as kidney stones and urinary tract infections. next to that it summarizes the consequences of dehydration, including constipation and headache and a decrease in physical and mental performance3.

In line with this review, the European Food Safety Authority (EFSA) (opinion 2075, April 2011) approved two health claims on health benefits of water; “Water regulates normal body temperature” and “Water maintains normal physical and cognitive functions”. As tea contains >99% of water, it can in fact be a large contributor to total water intake and all health benefits linked to it. Actually, our recent research26 has shown that black tea consumption improves attention and alertness; this evidence will be discussed in our next newsletter focussed on tea and cognition.

Water is the largest component of the human body, representing 45–70% of total body weight8. Fluid-electrolyte turnover and whole-body water

balance change constantly because water is lost from the lungs, skin, and kidneys, and because water is gained from food and fluids1,2. The normal daily water balance for a sedentary healthy individual of 70–75 kg living in a temperate climate shows an average daily water exchange of 2250 ml. Urine excretion usually accounts for about 1250 ml while the rest (1000 ml) is typically lost via sweating, respiration and elimination of faeces. Food generally accounts for 1000 ml of the daily water intake, metabolism for 350 ml and drinks from all sources for the remaining 1200 ml.5

Because of the wide variability within and between individuals, it is difficult to estimate a general water requirement. For the US population, Adequate Intake (AI) for total water was set based on the median total water intake from U.S. survey data (IOM, 2004). The AI for total water intake for young men and women (age 19 to 30 years) is 3.7 L and 2.7 L per day, respectively. The World Health Organization (WHO) recommends 2.5 L for women and 2.9 L for men under average conditions and intakes of 4.5 to 5.5 L under specific conditions such as during exercise, in hot climates or during pregnancy and lactation.9

1.2 thE contrIButIon of tEA to fluId IntAkEthanks to its popularity and flavour which makes it often a preferred beverage over water, tea is an important contributor to fluid intake in the diet. for example in the netherlands, daily consumption of 330–340 ml has been reported for men and 400–610 ml for women.10 In the uk, both men and women consume comparable amounts of tea, ca. 540 ml per day.11

In 2006, a guidance system for beverage consumption was proposed by a panel of US scientists. The panel ranked beverages from the lowest to the highest value for hydration based on

caloric and nutrient contents and related health benefits and risks. Drinking water was ranked as the preferred beverage to fulfil daily fluid needs, and was followed directly by unsweetened tea12. The panel recommended consumption of unsweetened tea up to 40 oz (ca. 1 litre) per day.

Next to water, green, black and oolong tea from the Camellia sinensis leaves contains theanine, flavonoids, and caffeine. In relation to hydration, most discussion has evolved around caffeine as an active in tea that may negatively influence water balance.