Can Dehydration Cause Insomnia? (Science-Backed)

More and more research shows that dehydration has a negative effect on both physical and mental processes.

Dehydration causes fatigue, anxiety, mood changes, and even cognitive impairment (1,2).

It’s natural to wonder if it can affect sleep as well, since symptoms like anxiety and depression are known risk factors of insomnia.

The research that we’ll summarize on this page shows that dehydration does cause insomnia, but the severity depends on the specific case.

The Link Between Short Sleep and Dehydration

The most comprehensive study to date on this topic was published in 2019, which examined national data from both the United States and China (3).

They found:

Short sleep duration (under 6 hours) was associated with higher odds of inadequate hydration in US and Chinese adults relative to sleeping 8 hr.

In other words, people who were regularly dehydrated were 1.42 times more likely to sleep less than 6 hours.

The most likely explanation that was highlighted was vasopressin regulation issues. Vasopressin is an antidiuretic hormone, which basically means that it’s released in order to tell the body to retain water, a key part of the circadian rhythm.

Normally, vasopressin is released late in sleep to modulate hydration levels, but people who are dehydrated have irregular levels of vasopressin during late sleep (4). In common terms, the body essentially says that dehydrated people sleeping need more liquid too early, so they wake up early to get it.

SummaryThere’s a significant link between dehydration and short sleep duration, which was found in multiple national populations.

Mild Dehydration May Not Affect Sleep Quality

While it only had 12 subjects, another study performed a controlled dehydration experiment on sleep quality (5).

Each participant spent a day in a dehydrated state (1.25 L of non-caffeinated fluids), and also a day with a “normal” (euhydration) fluid consumption (3 L or more of non-caffeinated fluids), in a random order.

It showed:

No significant differences were found in any of the examined indices of sleep quality and quantity between the dehydration and euhydration scenarios (p > .05). This is the first study to show that controlled mild dehydration does not seem to affect sleep quality and quantity in young healthy adults.

There’s a few things to mention here:

• One day of low fluid consumption will result in a different dehydration level than regularly not drinking much liquid.
• All the sleep quality metrics were a small amount worse in the dehydration group, it just wasn’t statistically significant. It’s possible that replicating this experiment with a larger sample size would change that conclusion.
• These were “healthy” young subjects. This conclusion may not apply in populations that are more at risk for sleep trouble (e.g. women, elderly)

SummaryWhile it’s not completely convincing, some research shows that mild dehydration doesn’t cause significant sleeplessness if it’s not a regular event.

Not All Dehydration Is Created Equally

Another study looked at the effects of dehydration caused by exercise on sleep quality (6).

Even if the dehydration itself had a negative effect, the benefits of exercise in this case more than made up for it:

Following exercise in hot conditions, participants reported an increased length and more efficient bout of sleep.

As the authors note in this paper, this is possibly just a short term effect, and someone who exercises a ton on a regular basis may have different results.

Dehydration in the Elderly

One potential explanation of why older people are more vulnerable to dehydration and insomnia is insensible water loss.

Insensible water loss refers to the water lost through the skin and from breathing. Research shows that this factor goes up as we age and contributes to aging related dehydration (7).

How Much Liquid Should You Drink?

One analysis of Europeans showed that approximately 20% of adults are dehydrated on a regular basis (8).

In the same analysis, the average water intake in euhydrated (“good” hydration) women was 2.42 L per day, and 2.8 L per day for males.

The chart below shows data for females, while the values were 10-20% higher in all categories for males.

The amount of water from food was relatively consistent, so it makes more sense to focus on the amount of water from beverages.

SummaryWhile it depends on the individual (i.e. larger people need more), drinking only 1.53 L (females) or 2.08 L (males) of water will likely leave you dehydrated.

The Type of Liquid Matters

Drinking a liter of water is not equivalent to drinking a liter of coffee.

Many beverages are diuretics, which means they promote urination. While you’ll still “gain” some hydration from coffee, it will be less than the equivalent amount of water.

The most common diuretics to avoid are:

• Coffee
• Energy drinks
• Alcohol
• Green tea

Additionally, all of these contain some level of caffeine, and caffeine is one of the common causes of insomnia; if you have to drink it, do it early in the day.

Preventing Dehydration That Affects Sleep

The solution to dehydration is pretty obvious: drink more water.

But there a few common sense tips to make this easier:

• Drink a large glass of water first thing in the morning. It will help you wake up and replace the fluids lost during the night. While you want to drink coffee (or tea) early on, it can wait until you’ve had some water first.
• Reduce drinking in the hours leading up to bed. Otherwise you may find that you have to get up frequently to urinate (9).
• Don’t drink diuretics at night. On top of usually having caffeine, the diuretic effect can interfere with your circadian rhythm.

At the same time, too much water can cause you to have to get up at night to go to the toilet.

In addition, drinking a ton of liquids can be dangerous, so don’t suddenly start drinking a huge amount.

Studies show that kidneys can remove no more than 0.8-1.0 L per hour, so drinking more than that in a short term period can cause serious health problems (10).

Summary: Dehydration and Insomnia

While more research is needed, there appears to be a clear link between dehydration and short sleep duration.

It’s unlikely that dehydration will prevent someone from getting to sleep, but it’s likely to cause an early wake up and can make it hard to get back to sleep. This is one of the main types of insomnia.

If someone is having insomnia that involves trouble getting to sleep, it’s likely caused by another factor.

References

1. Mild dehydration impairs cognitive performance and mood of men
2. Effects of hydration status on cognitive performance and mood
3. Short sleep duration is associated with inadequate hydration: cross-cultural evidence from US and Chinese adults
4. Preventing dehydration during sleep
5. Effects of controlled dehydration on sleep quality and quantity
6. Impact of Exercise-Induced Dehydration on Perceived Sleep Quality
7. Increased insensible water loss contributes to aging related dehydration
8. Water Intake and Hydration Indices in Healthy European Adults
9. Nocturia
10. Hyponatremia caused by excessive intake of water as a form of child abuse