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In the journals
Adults who sleep only six hours per night may have a higher chance of being dehydrated, compared with those who sleep longer, according to recent research published online Nov. 5, 2018, by the journal Sleep. The findings suggest that some of the symptoms of inadequate sleep, such as fatigue, fuzzy thinking, and headache in the morning, may be due to dehydration.
Researchers looked at the risk of dehydration in approximately 20,000 U.S. and Chinese adults. In both populations, people who reported sleeping six or fewer hours had up to a 59% higher risk of dehydration compared with those who slept seven to eight hours on a regular basis. The researchers speculated that the finding may reflect the nightly rhythm of a hormone called vasopressin. During sleep, the pituitary gland in the brain uses vasopressin to signal the kidneys to retain fluid in the body rather than excreting it through urine.
Normally, the pituitary gland releases more vasopressin later in the sleep cycle, so if a person wakes up early, less of the hormone reaches the kidneys in time to conserve water. Naturally the best remedy is to get more sleep. But if you can't, be sure to drink at least one full glass of water when you first wake up.