With the UK currently experiencing a significant heatwave, it feels only right to focus this week’s blog on staying hydrated. I love a beautiful summer’s day as much as the next person, but recorded temperatures of over 30 degrees throughout the day, not just in the middle of the day, puts you at serious risk of dehydration.

Hopefully, you have a good understanding of what dehydration is, but as a quick recap, dehydration is where you lose more water than you consume. As we’re composed of two-thirds water, it may seem difficult to easily lose enough fluid to cause harm. However, your body is so finely tuned that even the slightest change can have a devastating effect.

Water plays numerous roles in the body, and each of them is vital to our wellbeing and performance. Some of these roles include helping to maintain a constant internal temperature; helping to break down food through digestion; providing a medium for chemical reactions; transporting nutrients throughout the body in the bloodstream, and lessening the pressure on the kidneys to remove toxins.

When water levels are low, the body’s ability to regulate its own temperature is compromised, which can cause it to overheat. Enzymes—which control cellular reactions—prefer to work within specific temperature ranges, and their performance is impaired outside these levels. By raising your core temperature, you risk causing a decrease in your metabolism and cellular activity. This partly explains why we can all feel sluggish on hot days.

Proteins and carbohydrates are two nutrients essential for healthy bodily functioning. They provide energy and are vital for growth and development. However, these two substances are useless to the body without water. Water enables a chemical reaction to occur which results in proteins and carbohydrates becoming usable by the body. This is a secondary cause of heat-related fatigue or exhaustion.

In addition to this, reduced water in the blood makes it thicker, with three consequences. The first is a drop in the transport of nutrients, which impairs body functioning. The second is greater pressure on the heart to pump blood around the body, and the third is the additional strain placed on the kidneys to remove toxins.

With an understanding of how a drop in water level impacts the body, it’s now important to understand the different levels of dehydration and their associated symptoms.

We’ve all experienced dehydration at some point but most likely, hopefully, nothing too severe. Dehydration can be split into four categories: mild, moderate, severe, and fatal. During mild dehydration, the body loses 2–3% of its weight in water and the first indication is thirst. The effects will be minimal, and bodily functions are usually maintained with no real impact. At this stage, simply drinking water would be enough.

If we lose 3–5% of our body weight in water, the effects become a little more serious. You may experience dry skin, dizziness, headaches and intense thirst. Still not life-threatening at this stage, but unlikely to be a pleasant experience. It would be advisable to take in water with electrolytes—salts and sugars—to negate the effects.

As we continue to lose water and move into the 5–9% region, the consequences become more serious. You may develop a fever, high pulse, lack of sweat (which is normally used to cool the body), low blood pressure, and dark urine. At this stage, you need to take on water with electrolytes immediately and remove yourself from any heat-loss activity or setting that is causing you to lose water. If you don’t, you could end up in the final stage of dehydration, which I hope no one ever reaches, which is the fatal dehydration stage which includes delirium and loss of consciousness. At this stage, you are typically experiencing heat-stroke.

Heat-stroke is a condition where the body cannot regulate its own temperature so begins to get excessively hot—typically over 40 degrees. It’s caused, in part, by dehydration and can put a strain on the lungs, liver, kidneys and abdomen. It’s an extremely serious and potentially life-threatening condition. If someone gets heat-stroke, sit them in a cool room for 30 minutes and help them rehydrate. If the symptoms don’t begin to improve within that 30-minute period, call an ambulance.

The big question in all this is, how much should you drink to avoid dehydration? Unfortunately, this is an open-ended question and one that is difficult to answer. As each of us is different, there isn’t a one-size-fits-all approach, but the rule of thumb is two litres a day for the average adult in normal conditions for the UK. When it comes to exercise, an additional 0.5 litres is required for every hour of exercise. One of the best methods of monitoring dehydration is to look at the colour of your urine. You may have heard of this before but it really is a great way to see how hydrated you are. Pale yellow to clear is normal and indicates that you’re well-hydrated. Light yellow and transparent is also normal and indicates an ideal hydration status. Pale honey, transparent colour indicates normal hydration, but it may mean that you need to rehydrate soon. A yellow, cloudier colour means your body needs water. A darker yellow, amber colour isn’t healthy. Your body needs water. Orangish yellow and darker: you’re severely dehydrated. Contact your doctor immediately.