BIRMINGHAM, United KingdomGood news for coffee drinkers. New research published in the journal PLoS ONE found drinking moderate amounts of coffee does not result in dehydration and actually contributes to daily fluid requirements in regular coffee drinkers just as other fluids do.
Previous research showed the acute effects of caffeine as a mild diuretic, and there is a common assumption that caffeinated beverages, such as coffee, can cause dehydration. However, the effect of coffee consumption on fluid balance cannot be directly compared with that of pure caffeine.
Researchers at the University of Birmingham School of Sport and Exercise Sciences conducted the study to directly assess the effects of a moderate consumption of coffee compared to equal volumes of water.
"Despite a lack of scientific evidence, it is a common belief that coffee consumption can lead to dehydration and should be avoided, or reduced, in order to maintain a healthy fluid balance. Our research aimed to establish if regular coffee consumption, under normal living conditions, is detrimental to the drinker's hydration status," said Sophie Killer, a doctoral researcher and lead author of the study.
In a sample of regular coffee drinkers, the researchers measured the effects of moderate consumption of black coffee compared to the consumption of equal volumes of water on fluid balance and hydration status. Fifty male participants were tested in two phases, where they were required to drink four mugs (200ml) of either black coffee or water per day for three days. In the second phase, those who had initially consumed coffee switched to water and vice versa. The two phases were separated by a 10-day wash-out period. Females were excluded from the trial to control against possible fluctuations in fluid balance resulting from menstrual cycles.
To assess hydration status, the researchers used a variety of well-established hydration measures including body mass and total body water, as well as blood and urine analyses. The researchers found no significant differences in total body water or any of the blood measures of hydration status between those who drank coffee and those who drank water. Furthermore, no differences in 24-hour urine volume or urine concentration were observed between the two groups.
"We found that consumption of a moderate intake of coffee, 4 cups per day, in regular coffee drinking males, caused no significant differences across a wide range of hydration indicators compared to the consumption of equal amounts of water," Killer said. "We conclude that advice provided in the public health domain, regarding coffee and dehydration, should be updated to reflect these findings."
A separate report published by the Institute for Scientific Information on Coffee (ISIC) in December 2013, found regular, moderate coffee consumption may decrease type 2 diabetes risk by 25%. The report, outlined the latest research on coffee and type 2 diabetes, including epidemiological evidence showing that drinking 3-4 cups of coffee per day is associated with an approximate 25% lower risk of developing type 2 diabetes, compared to consuming none or less than 2 cups per day.
Research has also suggested an inverse dose response, with each additional cup of coffee reducing the relative risk of developing type 2 diabetes by 7%-8%. Caffeine is unlikely to be responsible for the protective effects of coffee, as both caffeinated and decaffeinated coffee are associated with a lower risk of type 2 diabetes.