Does Dehydration Cause Fatigue? Here's What a Dietitian Says

Your body is made up of 60% water. Drinking some H20 may help slay your sluggishness. Here's how to rehydrate right.

Many folks are familiar with the feeling of fatigue. Even if it's not a daily experience, you've probably felt tired and low on energy from time to time. But could it be a result of dehydration? The number of people who experience dehydration is tough to measure, especially when it comes to moderate dehydration, which probably affects many daily. The effects of dehydration may impact you in ways you don't even realize. In this article, we'll share the connection between dehydration and fatigue and how to ensure you're properly hydrated to feel your best.

What Is Fatigue?

According to the National Library of Medicine, fatigue is "a feeling of weariness, tiredness or lack of energy." That differs from wanting to sleep, which is considered drowsiness. Symptoms of fatigue, on the other hand, include:

  • Lack of energy
  • Lack of motivation
  • Feeling weary
  • Tiredness (often related to physical activity, boredom or emotional distress)

Fatigue can be a sign of an illness or a relatively harmless and normal feeling. Some illnesses associated with fatigue include iron-deficiency anemia, depression, thyroid disorders and sleep disorders.

What Is Dehydration?

According to the National Library of Medicine, dehydration is "a condition caused by losing too much fluid from the body. It happens when you lose more fluids than you are taking in, and your body does not have enough fluids to work properly." Common symptoms include:

  • Thirst
  • Dry mouth
  • Dry lips
  • Dry skin
  • Less urination
  • Less sweat
  • Dark-colored urine
  • Dizziness
  • Feeling tired

There are various levels of dehydration, from mild to severe. Severe dehydration requires hospitalization and intravenous fluids for rehydration, while mild dehydration can be reversed by drinking water or an electrolyte beverage. If you struggle to drink fluids throughout the day and notice some of the symptoms above, you may be mildly dehydrated and may benefit from upping your fluid intake.

a photo of a woman looking tired while holding a mug
Getty Images

What's the Link Between Dehydration and Fatigue?

Your lethargy or mental exhaustion might stem from being dehydrated. Here are two ways they're connected.

Fatigue Is a Symptom of Dehydration

According to the National Library of Medicine, fatigue is one effect of dehydration. You may feel extra sluggish, mentally and physically, if you're not taking in enough fluids. Among older adult women, those who were more hydrated had better attention and processing speeds compared to those who were less hydrated (or overhydrated), according to research in the European Journal of Nutrition in 2019. That said, many things can cause fatigue, and there can be many other symptoms of dehydration besides fatigue.

Dehydration Can Reduce Endurance and Muscle Strength

Several studies have evaluated the effect of dehydration on athletic performance, including on measures of endurance and fatigue. For example, a 2018 study published in Frontiers in Physiology found that combat sports athletes who were dehydrated reported feeling more fatigue and experienced reduced muscle-strength endurance.

Another study, published in 2018 in The Journal of Strength & Conditioning Research, examined the effects of dehydration on mixed martial arts athletes. They found that strength and endurance were worse for those who were purposely dehydrated than for members of a control group, even 24 hours after they were allowed to rehydrate.

How to Ensure Proper Hydration to Prevent Fatigue

Given that dehydration can lead to some not-so-pleasant symptoms, including fatigue, you may wonder how to stay hydrated. The Institute of Medicine recommends adults consume 2.7 to 3.7 liters of water daily, depending on age and sex. (That's 91 to 125 ounces of fluids per day.) Water can come from plain water, other liquids or water-rich foods like fruits, vegetables and soups.

In addition, the amount can vary depending on climate, physical activity and health conditions. For example, if you live in a hot climate and are very physically active, your fluid needs will likely be higher than someone living in a cold climate who is sedentary.

One of the best ways to check your hydration status is to monitor your urine. Ideally, your urine should be a pale yellow color. If it's dark yellow or amber-colored, you probably need to drink more fluids. You can also consider how often you're urinating. Urinating every two to three hours usually signals adequate hydration.

Of course, water is a great option to promote hydration. However, if you get bored with water, there are other options out there. Here are some ideas:

  • Consume fruits and veggies. These have a high fluid content and contribute to your fluid intake.
  • Add fruit to your water; boosting flavor may help you consume more.
  • Try sparkling water to add variety.
  • Have a glass of low-fat milk or 100% fruit juice.
  • Consume tea or coffee in moderation.

Frequently Asked Questions

How can you identify fatigue due to dehydration?

If you're feeling tired and low on energy, do a self-check to see if you're also experiencing symptoms of dehydration, such as dry mouth, thirst or infrequent urination. If you notice these symptoms, your fatigue may be related to dehydration.

What's the fastest way to fix fatigue due to dehydration?

Research shows it may take some time to bounce back from dehydration-related fatigue. However, as soon as you notice signs of dehydration, drink some fluids. If you're very dehydrated due to diarrhea, vomiting or an intensely sweaty workout, you may want to opt for a sports drink with electrolytes or an oral rehydration solution over regular water.

What are the signs of dehydration?

Common signs of dehydration include dry mouth, thirst, infrequent urination, fatigue, dizziness, dry skin, dry lips and dark-colored urine. These are all signs that you could use more fluids.

How much water should you drink to rehydrate?

The amount of water you need to rehydrate will vary based on how dehydrated you are. In fact, if you are very dehydrated, especially if it's related to diarrhea, vomiting or sweat, you may even need to drink an oral rehydration solution.

The Bottom Line

Dehydration can cause numerous symptoms, one of which is fatigue. The best way to rehydrate depends on how dehydrated you are and the root cause. Be mindful of symptoms of dehydration like dark-colored urine or infrequent urination, and act fast to add more fluids. Dehydration-related fatigue can take some time to resolve after rehydration, so stay mindful of your fluid intake every day to prevent dehydration in the first place.

Was this page helpful?
Related Articles