Tired But Wired? Research Says You Might Just Be... Thirsty
When I can’t fall asleep, I usually blame my phone, my stress levels, or that 4 p.m. coffee. But what if the real culprit is something far simpler…dehydration.
According to a new study1, even mild dehydration can make it harder to drift off—and leave you feeling groggier the next morning, even if you technically slept longer.
It’s a small but important reminder that one of the most basic biological needs (aka hydration) could be quietly shaping how well we rest.
How hydration impacts sleep
For this study, researchers tracked 18 healthy young adults over four consecutive days, each under a different hydration condition: baseline, well-hydrated, mildly dehydrated (after 24 hours of limited fluids), and rehydrated.
Each morning, participants filled out a validated sleep diary assessing how easily they fell asleep, how long they slept, and how refreshed they felt. The researchers also confirmed hydration levels through urine samples and body mass changes, so this wasn’t just about “how thirsty” participants felt.
The results were surprisingly clear:
- When mildly dehydrated, people took longer to fall asleep.
- They actually slept about an hour longer (7.5 hours vs. 6.4 hours when hydrated), but woke up feeling more tired.
- Once they rehydrated, both their sleep onset and fatigue levels improved.
In other words, dehydration seemed to trick the body into sleeping longer, but not better.
Why being a little dehydrated messes with your sleep
It might sound strange that water intake could affect something as complex as sleep, but it makes sense when you zoom out on how interconnected the body really is.
Dehydration influences the brain’s neurotransmitters, especially dopamine and norepinephrine, which regulate attention, motivation, and fatigue. When hydration dips, these systems falter, making us feel more sluggish and mentally foggy.
That “extra hour” of sleep in the dehydrated state may actually reflect the body’s effort to recover from that fatigue, not deeper rest.
Hydration also impacts the hypothalamus, the same brain region that controls both fluid balance and circadian rhythms. When fluid levels drop, your body’s internal clock can misfire, disrupting melatonin production and making it harder to fall asleep.
And because dehydration increases heart rate and core body temperature (two things that naturally decrease as you prepare for sleep), it essentially works against your body’s built-in bedtime signals.
Mild dehydration is more common than you think
If you’re thinking, “That doesn’t apply to me—I drink plenty of water,” you might be surprised. Studies estimate that 25–30% of adults are mildly dehydrated on any given day, often without realizing it.
You can reach that point by simply drinking less than 1.5 liters of water in 24 hours, sweating more than usual, or consuming extra caffeine or alcohol, both of which increase fluid loss.
Mild dehydration (a 1–2% loss in body weight from fluids) can subtly affect everything from mood and focus to metabolism and, as this study suggests, sleep quality.
How to stay hydrated & sleep better
Supporting deeper sleep could be as easy as adjusting how (and when) you hydrate:
- Front-load your fluids: Try to drink most of your water before midafternoon. Chugging a full bottle before bed can backfire by waking you up for bathroom breaks.
- Add electrolytes: Support hydration by replenishing key minerals like sodium, magnesium, and potassium.
- Eat your water: Hydrating foods like cucumber, citrus, watermelon, and yogurt can contribute significantly to daily intake.
- Pay attention to your cues: If you’re frequently thirsty, have dark urine, or feel tired for no reason, hydration may be part of the puzzle.
RELATED READ: 5 Signs Your Body Is Begging You For More Electrolytes
The takeaway
Hydration isn’t just about energy and performance; it’s also about recovery and rest.
Before reaching for melatonin or changing your bedtime routine, consider checking your water bottle instead. Your brain, hormones, and circadian rhythm all depend on steady hydration to do their jobs—and a well-hydrated body is a body that sleeps (and wakes) more easily.
So next time you find yourself staring at the ceiling, maybe skip the scroll and sip some water instead.
