The Weird Side Effect of Sleeping 6 Hours (or Less) a Night

Updated: Jan. 20, 2021

Six hours never feels like enough sleep. Turns out, it’s not.

There’s plenty of research out there underscoring how crucial sleep is for maintaining your weight, focus, stamina, healing powers, and general health. Now there’s another reason to get your beauty sleep: Six hours or less of slumber a night can leave you dehydrated.

In a study from Penn State, published in the journal Sleep in 2019, researchers analyzed sleeping habits and urine samples in more than 20,000 adults in the United States and China. They found that people who slept six hours on average were up to 59 percent more likely to be dehydrated than adults who slept eight hours on a regular basis at night. This suggests that feeling awful after a poor night of sleep may also be attributed to this resulting dehydration, not just to a lack of sleep. (Find out the other surprising things that happen to your body when you don’t get enough sleep.)

The study noticed that vasopressin, a hormone that regulates the body’s hydration status, is released toward the end of a sleep cycle. “Vasopressin is released both more quickly and later on in the sleep cycle,” said lead author Asher Rosinger, PhD, assistant professor of biobehavioral health and anthropology at Penn State, in a press release. “So if you’re waking up earlier, you might miss that window in which more of the hormone is released, causing a disruption in the body’s hydration.”

Michelle Drerup, PsyD, Director of Behavioral Sleep Medicine at Cleveland Clinic, who is not associated with this study, says that these findings are in line with other research on hormones and sleep. “Our hormones have a circadian rhythm as well,” she explains. “We think of the sleep/wake cycle as being a circadian rhythm, but our temperature varies on a circadian pattern and our hormone levels, including our appetite hormones, are on a circadian pattern as well, so this finding about vasopressin makes sense.” (Here’s how circadian rhythm disorders can affect your sleep.)

To combat this problem, getting more sleep is obviously a good idea. (If you’re having trouble getting enough shut-eye, check out these 50 ways to sleep better.) Furthermore, Rosinger says, drinking water throughout the day is important—and it’s even more critical the morning after a poor night of sleep. “If you are only getting six hours of sleep a night, it can affect your hydration status,” he explains. “This study suggests that if you’re not getting enough sleep and you feel bad or tired the next day, drink extra water.”

And it’s not only important to keep yourself sufficiently hydrated to feel better. In a review of numerous studies on dehydration published in the Annals of Nutrition & Metabolism, researchers found that dehydration has a consistent, worsening effect on mood and that it can also impact cognitive performance, particularly in children and the elderly. In the long term, if you’re experiencing dehydration on a regular basis, it can lead to kidney stones or urinary tract infections. Make sure you know these surprising dehydration symptoms and also check out these ways that an extra hour of sleep could save your life.