Are you dehydrated?

Dehydration is a controllable risk factor that can affect a Service Member’s job performance, health, and safety, as well as overall unit readiness. However, by routinely assessing weight (W), urine color (U), and thirst (T), Service Members can check for dehydration throughout the day. Known as the WUT method, this practical, time-efficient, accurate tool can help measure your hydration status at home or in the field. When WUT criteria add up to 2 or 3, it’s time to rehydrate. Learn how to use the WUT method to help promote best practices for both individual and unit hydration.

What is dehydration?

Water is the most abundant molecule in the human body and is essential for you to function. However, your body regularly loses water through the skin (sweat), lungs (breath), kidneys (urine), and gastrointestinal tract (stool). Therefore, you need to replace it by consuming fluids to maintain the balance of water in your body. Your hydration status changes throughout the day depending on how much fluid leaves your body versus how much fluid you take in. So, it’s important to monitor your hydration status regularly.

Dehydration is a process that occurs when your body loses more fluid than it takes in. Extreme environments and extended periods of activity or operations outdoors can greatly increase the risk of dehydration, especially through sweat loss. Whether you’re turning wrenches on a flight line or rucking over miles of terrain loaded down with gear, you’re likely to experience fluid loss at rates that are hard to keep up with. To add to the challenge, sweat rates vary among individuals, making it difficult to establish a standard amount of water to maintain hydration levels, posing a significant challenge to unit-wide hydration status.The goal for every Service Member is to balance fluid loss with fluid intake to maintain good hydration.

Did you know? There are several technical terms used to describe differences in hydration status. “Dehydration” and “rehydration” are the processes of losing or gaining body water, respectively. “Hypohydration” is the state of having low body water (hypo- means “beneath” or “below”). “Euhydration” is the state of having adequate or optimal body water (eu- means “good” or “well”).“Hyperhydration” is the state of excess total body water content (hyper- means“excess”). While it’s common to use dehydration and hypohydration interchangeably, they are different.

What are the effects of dehydration?

Water plays a key role in all physiological functions in the human body. Therefore, dehydration can affect:

  • Physical performance. Dehydration leads to increased cardiovascular stress, increased sense of effort, and decreased physical performance. When you lose more than 2%–3% of body mass due to fluid loss, your aerobic and endurance performance are significantly impaired, particularly in hot, humid, or high-altitude environments.
  • Cognitive performance. Even mild dehydration (as little as 1–2% decrease in body mass due to fluid loss) negatively affects vigilance, working memory, visual-spatial function, reaction time, and mood, and contributes to fatigue. Fluid losses greater than 2% lead to changes in brain structure and decrease skill execution, alertness, and concentration.
  • Thermoregulation. Sweating is critical to maintain body temperature. If you don’t replace water lost through sweat (or other ways) with fluids, dehydration results, decreasing your body's ability to sweat and regulate its temperature (“thermoregulate”). Losing more than 2% of body mass due to fluid loss reduces your ability to sweat and increases the risk of heat illness.
  • Occupational performance, safety, and mission success. Decreases in physical and cognitive performance are likely to affect job-related duties and outcomes. For example, in high-performance aircraft pilots, more than 2% loss of body weight due to dehydration can decrease flight performance scores and G-tolerance up to 50%. Reduced performance may lead to mistakes and risk mission success.

How to tell if you’re dehydrated

Most methods to assess hydration status require advanced laboratory techniques or equipment and aren’t practical in most settings. However, a combination of three easy-to-collect measurements (weight, urine, and thirst) in a “Venn diagram” decision tool (see below) can be used to accurately measure hydration status. This method is proven to be comparable to hydration measures used in laboratory settings. Known as the WUT method, this model is now widely used for healthy, active, low-risk individuals to self-monitor their day-to-day hydration status. The “Dehydrated? WUT to Look For” handout that accompanies this article can help you easily assess your WUT markers and hydration status almost anywhere. No single marker is a true reflection of hydration status, but research indicates that testing positive for 2 or 3 of the WUT markers is a valid indicator of dehydration.

Three overlapping circles showing: W = Weight U = Urine  T = Thirst Where Weight and Thirst circles overlap: Likely Where Thirst and Urine circles overlap: Likely Where Urine and Weight circles overlap: Likely Where all three circles overlap: Very Likely

✔ Weight: Check the scale. “W” refers to percent (%) loss of body mass (weight). Monitoring your body mass is a simple, noninvasive, valid method to assess hydration status when you aren’t trying to gain or lose weight. When you replace water losses throughout the day, your body weight should change less than 1%. Therefore, 1% or more of weight loss is a marker of dehydration and counts as “1” in the WUT criteria.

To find 1% of your body weight, divide it by 100 (or multiply it by 0.01). For example, for a 220 lb Service Member:

220 lb / 100 = 2.2 lb weight loss 

(or 220 lb × 0.01 = 2.2 lb weight loss)

✔ Urine: Check your urine. “U” refers to changes in urine color. When you’re well hydrated, normal urine color is “very pale yellow,” “pale yellow,” or “straw-colored”—numbers 1, 2, or 3 on an 8-color urine scale (see below).  Urine color darker than 5  is a marker of dehydration and counts as “1” in the WUT criteria. Decreases in urine volume and urinating less often (more than 4 hours between voids) are also indications of dehydration. 

For the WUT method to be a valid tool for medical professionals to assess and identify dehydration, urine color should be assessed undiluted (such as in a urine-collection cup) and then compared against the 8-color urine color chart developed by Lawrence Armstrong in 1994 (see references below).

Diagram with 8 colored squares numbered, left to right, 1 through 8, increasing in color from pale yellow to dark brownish yellow.

✔ Thirst: Check in with your body. “T” refers to a conscious desire for water—thirst. If, like many people, you have learned to override internal body cues and ignore feelings of thirst, it’s time to reconnect your mind with your body. When using the WUT method, thirst is assessed on a scale of 1 to 9, where 1 is “not thirsty at all,” 3 is “a little thirsty,” 5 is “moderately thirsty,” 7 is “very thirsty,” and 9 is “very, very thirsty.” A thirst level of 5 or more is a marker of dehydration and counts as “1” in the WUT criteria.

How to prevent dehydration using the WUT method daily

You can use the WUT method daily to assess changes in hydration status. To get started, measure your weight 3 days in a row (under similar conditions) to get an accurate baseline body weight. It’s very important to weigh yourself at the same time each day, after urination, and in comparable clothing. So, choose a time and conditions that work for you and be consistent. Do you weigh yourself first thing in the morning, after voiding, with no clothing? Great! Keep those conditions similar for accurate baseline body-weight assessment. Or do you weigh yourself between 1500–1600 regularly, after voiding, in PT clothing before you hit the gym? Wonderful! Keep those conditions the same.

Now that you have an idea of your baseline body weight, you can watch for changes in body weight from day to day. Whenever you assess your weight, be sure to consider your urine color and feelings of thirst too. This way, you can use the WUT method on a regular basis to assess hydration status and help determine if you need to consume more fluids.

How to prevent dehydration using the WUT method for activities

Once you know your baseline body weight, you can also use the WUT method before, during, and after activities to determine if and when you need fluids to optimize your performance for specific events. Whether you’re getting in an afternoon workout or going out on an operational exercise, the goal is to begin well hydrated. Run through the WUT method about 4 hours before your activity to determine if you need more fluids to begin well hydrated. This gives you enough time to slowly drink fluids before the activity begins. This is particularly important if you know that you won’t have access to fluids during the activity. Consuming fluids with sodium, salted snacks, or small meals with salt can help you retain fluids and optimize your hydration status.

During activity, you may not be able to monitor body-weight changes. However, you can continue to assess feelings of thirst, and you may be able to assess urine color (if the activity is long enough and allows for bladder relief). These 2 WUT criteria can help you make hydration decisions throughout prolonged activity. As a standard practice, continue to take small sips of fluid throughout an activity to help minimize changes in urine color, body weight, and feelings of thirst during the activity.

After the activity, use the WUT method again to assess your hydration status, and rehydrate if necessary. If you retain proper hydration levels by consuming fluids during activity, then no specific rehydration strategies are needed. Keep in mind, if you gained weight during the activity, you might be consuming too much fluid. However, if your WUT criteria add up to 2 or 3 after activity, it’s time to rehydrate.

What do I do if I’m dehydrated?

Rehydrate! Your goal is to replace any fluid and electrolytes lost. Changes in body weight that reflect fluid loss can be used to calculate fluid-replacement needs at that time. If dehydration isn’t severe, and time permits, you can slowly consume normal meals and fluids to restore your hydration status over time. However, if recovery time is short (less than 12 hr), you can rehydrate by consuming about 1.5 liters of fluid for each kilogram (20–24 ounces for each pound) of body weight lost during activity. Consuming carbohydrates and electrolytes with rehydration fluid can help stimulate your thirst, retain fluid, and promote rehydration. Consider consuming options such as sports drinks, milk drinks, or food (such as salted pretzels) along with water.

Caution! Don’t drink more than you need. If you consume too much fluid, hyponatremia (low sodium levels in the bloodstream) can occur. Hyponatremia is less common than dehydration, but it can be more dangerous. As sodium levels in the bloodstream fall, you could experience symptoms such as headache, vomiting, fatigue, confusion, and disorientation. As the condition worsens, it could lead to cerebral edema (swelling of the brain) with seizure, coma, and even death.

Know when to ask for help

If dehydration continues without correction, you could develop more severe signs or symptoms, such as flushed skin, apathy, dizziness or lightheadedness, nausea, diarrhea or vomiting, chills, headache, gastrointestinal cramping, and discomfort. When weight loss due to dehydration is more than 2%, the effects on physical and cognitive performance may become more apparent. In these situations, it’s important to notify a team member, leader, or healthcare provider for continued care. Understanding the signs of dehydration, in daily life and during operations, can help you correct fluid balance with rehydration strategies to improve performance, reduce risk, and increase chances of mission success.

Fluid losses and needs vary a lot from person to person. Characteristics such as body weight, genetics, heat acclimatization, type and intensity of activity, differences in clothing, and environmental conditions can all impact fluid loss. Therefore, what’s “right” for you may not be “right” for your fellow Service Member. Regularly assessing your WUT and referring to the “Dehydrated? WUT to Look For” handout can help you stay on top of your hydration status and fluid needs.

Link to Dehydrated? WUT to Look For handout

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