How To Tell If You're Dehydrated—And What To Do About It

Whether it's 30 degrees Celsius and sunny or a cool 10 degrees, it's imperative to stay hydrated. Proper hydration helps you to meet specific performance goals and, most importantly, to ensure your body is functioning optimally.

The most simple definition of dehydration is "when you're losing water balance in the body", said Hannah Kittrell, MS, RD, CDN, and director of the Mount Sinai Physiolab in New York City. It's directly related to thirst and occurs when you're not drinking enough fluids to meet the amount of water that you're losing in daily life, she said.

"Dehydration occurs when the amount of water that you've lost in a given time period exceeds the amount of fluid that you've replaced it with", said Kaitlyn Baird, a clinical exercise physiologist at NYU Langone's Sports Performance Center in New York City.

To better tackle dehydration, it's important to understand the role of the kidneys. This vital organ balances the amount of water in the body and ensures the blood has the appropriate concentration of electrolytes and other minerals and nutrients in it, Kittrell said. To sum it up: when you're dehydrated, you're losing the water in the blood, which can lead to fluid imbalances and imbalances of different minerals.

The symptoms of dehydration can vary from person to person, with thirst, dark-coloured urine and infrequent urination (barring underlying conditions and disease) being the most classic symptoms, according to Baird and Kittrell.

"Very dark urine means it's more concentrated with different nutrients, so that could be a sign that you're dehydrated and need to drink more, whereas the pale yellow colour would be normal hydration status", Kittrell said. "And in terms of frequency in urination, if you're going every two to three hours then you're probably well hydrated. If it's a lot longer between bouts, then that could be a sign that you're dehydrated".

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Other symptoms of dehydration in adults include feeling fatigued, lethargic and tired. Some not-so-obvious symptoms include headaches, dizziness, lightheadedness, confusion and memory loss. Having a high heart rate, specifically your heart beating faster than normal, swollen feet, constipation and at times muscle cramping are also less obvious symptoms of dehydration, according to Baird.

Most people depend on thirst to tell if they're dehydrated, said Kittrell, because it's triggered by high fluid concentrations in the blood. When you sweat, you begin to lose water from the blood, causing the blood to become highly concentrated with electrolytes and other minerals. This signals thirst as your body tries to bring your blood concentration back to a normal range.

Although thirst is arguably the most recognisable sign of dehydration, Kittrell explained that it can be unreliable for recreational and professional athletes alike. Often your brain doesn't recognise the signal for thirst during physical activity or you simply don't feel thirsty and, by the time you do, you may have already lost one percent of your body weight via sweat. This can then cause your heart to work harder to circulate blood throughout the body.

Dehydration during physical exercise will also decrease your athletic performance and make everything feel harder, Baird said.

"It increases your sense of effort and your strain because your body is already trying to pump all this blood to your working muscles and, if you don't have enough hydration, it's harder for your body to pump that blood, so it's going to increase the feeling of strain", she said.

Aside from experiencing symptoms like thirst and fatigue, dehydration can lead to muscle cramps, due to the electrolyte imbalance, Kittrell said. She added that more extreme levels of dehydration can lead to heat stroke, heat shock, nausea, vomiting, confusion, disorientation and can even be fatal if you're severely dehydrated.

Conversely, if you drink too much water, it can lead to hyponatraemia—a condition that occurs when you don't have enough sodium in your blood—and you may exhibit symptoms similar to those of dehydration like feeling tired, bloated and nauseated.

Because the sensation of thirst is often blunted by exercise, it's advised to be proactive with hydration and drink plenty of fluids before you become thirsty, "because if you're waiting to drink until you're actually feeling thirsty, you're probably already a little bit dehydrated", Kittrell said.

One easy way to stay hydrated is by eating foods with a high water content such as watermelon, cucumbers, strawberries, grapefruit, soups and celery, Baird said. She also recommended making a habit of drinking a glass of water in the morning and evening to improve your hydration levels.

For the average person, the general recommendation is to drink eight cups of water a day, but variables such as sun exposure, duration of exercise, heat and humidity will influence your hydration needs. This is why Kittrell recommended focusing on your hydration before, during and after a workout. And, if you're doing endurance training that lasts a long time, not only do you need to rehydrate during training, but you'll also need to refuel, Baird said.

Before training, Kittrell said the goal is to make sure you enter your workout in a balanced fluid state. As more research comes out—in addition to experts realising how individualised fitness is—experts now make bodyweight recommendations for hydration instead of prescribing a generalised amount of fluid intake. Kittrell admitted that these individual recommendations are more complicated, but emphasised that they're better since they use a personalised approach.

Three to four hours before exercising, Kittrell recommended you consume 2ml to 3ml of water per 0.45kg of bodyweight. Then about five to 15 minutes before hitting your workout, it's recommended you have a few sips of water.

Another key to staying hydrated is to know your sweat rate. This can be figured out by weighing yourself before and after exercise to see how much weight you lost. If you can't measure your sweat rate, Kittrell said to stick to periodically drinking fluids throughout your training session. If you're doing a longer workout, she advised drinking around 240ml of fluids every 15 to 20 minutes, but noted that this depends on the conditions you're training in and the length and intensity of the workout.

Water is always a great option when it comes to fluid intake, but there are certain situations where sports drinks are warranted, according to Kittrell. The weather, specifically heat and humidity, how much sun there is, your sweat rate and the length of your workout are all variables to consider when deciding whether or not to have a sports drink. For those who are participating in activities where equipment is required, such as American football, a sports drink is recommended as the additional gear will cause you to lose more sweat.

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Understanding your sweat rate is one of the best ways to understand your body and hydration needs and measuring your sweat rate is fairly simple. You can purchase patches to measure your sweat rate, but weighing yourself before and after exercise (nude or with as little clothing on as possible post-workout) will also suffice. As a general rule of thumb, if you lose two percent of your body weight of fluid during exercise, you're dehydrated. Losing more than two percent means you've reached excessive dehydration, which can also lead to significant impairments in aerobic exercise, Kittrell said.

"For every 0.45kg lost during exercise, drink 80 to 100 percent of that loss in water", Kittrell advised. Losing 0.45kg equates to about 470ml, so for every 0.45kg you lose during exercise, drink around 380ml to 470ml of water, she said.

These are just recommendations and Kittrell advised experimenting with your fluid intake, especially if you don't drink a lot during training sessions to avoid gastrointestinal issues.

"As it goes with anything, you don't want to implement something new on game day or race day, you definitely want to have experience with it in your training runs and your practices to see what works best for you", she said.

Dehydration is not something to take lightly and can have serious implications. It's important to understand and recognise the signs and symptoms of dehydration. It's also important not to write off dehydration as simply being tired and working hard. In the event that you might be dehydrated, Baird recommended immediately stopping activity, moving to a shaded or air-conditioned area and placing a cool towel around your neck or on your head. Get a cold drink (water or sports drink) and let someone know what you're experiencing. These tactics can help to avoid entering a heat stroke zone.

"I know it's hard to tell the difference sometimes [between dehydration and working hard], but being aware and taking the right steps if something doesn't feel right is essential for your safety", Baird said.

Words by Tamara Pridgett