A study from researchers at Penn State has revealed a new reason why getting less than the recommended eight hours of sleep a night could be damaging to our health. The research found adults who only got around six hours of sleep per night were more likely to be dehydrated, and the cause could be a particular hydration-regulating hormone that is released late in a person's sleep cycle.

The study looked at 20,000 adults across three samples, spanning the US and China. Sleeping habits were surveyed, and urine samples were gathered from all participants. The results found across all three samples that those adults reporting around six hours of sleep per night were between 16 and 59 percent more likely to be dehydrated compared to those regular eight-hour sleepers.

The study's findings are, at this stage, just an observational association, so no definitive causal connection can be clearly made, however, the researchers do propose a potential causal explanation for this connection between shorter sleep duration and hydration.

One of the fundamental hormones that regulate our body's hydration is called vasopressin. Research from McGill University in 2010 suggested that vasopressin levels are modulated in conjunction with a person's circadian rhythm. This is essentially how our bodies are set to store water while we sleep, so we don't over-produce urine and become dehydrated from not drinking across eight-hour stretches of slumber.

The 2010 research hypothesized that vasopressin levels increase during sleep, particularly in later sleep cycles. It is this mechanism, the researchers behind this new study suspect, is responsible for the correlation between shorter sleep duration and inadequate hydration.

"If you are only getting six hours of sleep a night, it can affect your hydration status," says lead author on the new study, Asher Rosinger. "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."

The researchers do stress that this new study is just an observational association and the causal hypothesis is just that, a hypothesis. The next stage for the research is to try to verify the relationship between sleep and hydration across a longitudinal study examining single subjects over the course of a week.

Nevertheless, Rosinger does suggest that this research may help explain why some people feel unwell, or out of sorts, after a shortened night of sleep. They may be mildly dehydrated, and the advice is to drink additional water on days following shortened nights of sleep.

The new research was published in the journal Sleep.

Source: Penn State