STORRS, Conn.— For decades, health and exercise experts have cautioned
that caffeine causes dehydration – despite a dearth of scientific evidence to support
that notion. A new study conducted at the University of Connecticut’s Human
Performance Laboratory, however, shows that consuming the equivalent of two
to four cups of coffee a day causes no more dehydration than drinking water.
how much caffeine Americans consume. If the myth is true, why aren’t hospitals
filled with severely dehydrated people?” asked Larry Armstrong, a professor
of exercise science and environmental physiology in UConn’s Neag School of
Education, who led the study.
studies have shown that caffeine acts as a mild diuretic over the course of one to
three hours, none of them yielded any evidence that caffeine consumption coupled
with exercise produces chronic dehydration, as the medical establishment has warned,
diuretic effect does not equal dehydration,” Armstrong explained.
Armstrong’s study is the first laboratory investigation of caffeine consumption
and hydration status, electrolyte balance and renal function to last longer than
Researchers at UConn’s Human Performance Lab gave 59 moderately active men
between the ages of 18 and 34 controlled amounts of caffeine for 11 consecutive
days. All of the men ingested capsules with 226 milligrams of caffeine – the
equivalent of two cups of coffee – daily for the first six days of the study.
For the final five days, one third of the group was given placebos or pills
without any caffeine; one third of the men maintained the same level of
caffeine (226 milligrams daily) and the remaining third
took capsules with 452 milligrams of caffeine – or the equivalent of four
cups of coffee – daily.
Among Armstrong’s findings:
- Men in all three groups showed similar levels
of hydration for the entire duration of the study
(20 measures of hydration status were used);
- There were no discernable differences in whole-body
electrolyte balance (sodium and potassium) and renal
function in any of the men, based on diet intake
records and excreted electrolyte measurements; and
- All of the men maintained their regular regimens
of moderate exercise, including running, biking and
resistance training, during the 11-day study and
still none of them showed increased signs of dehydration,
electrolyte imbalance or impaired renal function.
findings show that the health and performance of athletes and active adults will
not be impaired if they consume caffeine or caffeinated beverages in moderation,” Armstrong
said. “This is contrary to the advice of most nutritionists, athletic trainers
avid runner and well-respected scientist who has been conducting fluid balance and
body temperature regulation research for 25 years, began studying caffeine consumption
and hydration status after observing that his own experiences did not conform to
conventional wisdom on the subject.
In 2002, he published a research review study that concluded no scientific evidence
existed to suggest that moderate caffeine consumption contributed to chronic dehydration.
study, funded by the Washington-based International Life Sciences Institute, used
a controlled, randomized, double blind design.
His findings were published in the International Journal of Sport Nutrition
and Exercise Metabolism earlier this month.