Let's talk about hydration!

Hello MRC! Today, I’m here to talk to you about hydration. So, grab a glass of water and settle in…

We’ve been experiencing some glorious weather recently, and whilst it makes a welcome change from cloud and drizzle, the sun and the increased temperatures can cause a few issues for us as runners. It’s a subject I’ve recently become passionate about, since running the 4^th hottest London Marathon on record this year (2025), and witnessing first-hand just how awful the effects of dehydration and heat exhaustion can be. So, I thought it might be worth sharing some tips I picked up along the way and the reasons why they are helpful.

Common Sense Disclaimer – I am not a medical professional. All tips are referenced in articles I have read, as well as my own experience.  I have avoided putting figures on exactly how much liquid anyone should drink (aside from the well published 6-8 glasses of water) because without expert knowledge or testing, it’s impossible to know. As humans, we’re all built differently. What’s important is that we get to know our own bodies and what they need in order to perform well and stay healthy. The information provided below is a rough guide.

Let’s begin with the symptoms of dehydration – so we can listen to our bodies and understand what we’re trying to avoid:

·         dry mouth

·         fatigue

·         dizziness

·         headache

Dehydration is guaranteed to impact running performance, enjoyment, and will, at best, make you feel a bit rubbish. At worst, dehydration risks exacerbating existing medical conditions, such as asthma, heart conditions, and can cause urinary tract infections, and more... At the very worst, continued exertion in hot weather, whilst dehydrated, could lead to heat stroke.

What contributes to dehydration?

Dehydration occurs when your body loses more fluid than you take in. As members of MRC, we’re likely to think of sweating whilst running as a top contributor. However, lifestyle factors also play a big role. How many of us don’t drink as much liquid during the day as we should? We’re too busy, day full of meetings, rushed off our feet, or simply forget. Sound familiar?

What about caffeine? It’s complicated. Although caffeine is a diuretic, meaning it increases urine production, which in theory can contribute to dehydration, studies have shown that the volume of liquid in coffee tends to balance out the effect of caffeine in relation to dehydration. However, there are other factors that can influence its effect on your system, such as difference in tolerance between individuals (we’re not all the same). To be on the safe side, you could aim to alternate cups of coffee with a glass of water, or decaff.

Caffeine gels during a race? Most brands recommend balancing these with a suitable amount of water to prevent dehydration. Make full use of those aid stations!

How can we hydrate more effectively?

Got that dry mouth feeling? Grab a glass of water! Fill a bottle and put it on your desk and sip regularly. Set reminders in your phone to hydrate!

It’s obvious to most people that if you exercise, you’re going to need to drink, possibly during (depending on the duration of activity, level of exertion and individual needs), and definitely afterwards, to replace fluids lost through sweating. So, taking some water with you on your run is always a good idea during periods of hot weather, and having a drink to hand for afterwards too.

That said, it takes more than a big glass of water to properly hydrate our bodies. We need to be drinking 6-8 glasses of water a day, and prior to a training run or race, additional liquids up to 2-3 days before! If you’re planning to join us on a Wednesday evening over the Summer, or you have Summer races in your calendar, it’s worth checking the weather forecast in advance to see if you need to start drinking more over the preceding days.

The other thing to be aware of is electrolyte loss and potential imbalance. Electrolytes are essential minerals that help regulate the body's fluid balance, nerve and muscle function, and other vital processes. Dehydration can also lead to electrolyte imbalances. Electrolyte imbalances, in turn, can worsen dehydration and cause a range of symptoms, from mild (like muscle cramps) to severe (like cardiac or neurological issues). 

Therefore, it’s also important to make sure that we include electrolytes in our hydration process. My personal favourites are Hi-5 electrolyte tabs, which you can just pop into a bottle of water. There are loads of flavours and they taste just like fruit squash. I drink at least 500ml with electrolytes each day in the 2 days preceding a summer race / club run.

Saltstick fast chews are great for replacing electrolytes during races as they taste like Refreshers and work almost instantly. They dug me out of a fuzzy-headed hole during the London Marathon. They are also really small and fit in a pocket / bumbag. Other club members have informed me that they help enormously with muscle cramps.

You can also make your own electrolyte drinks at home.

How will I know if I’m hydrated enough?

The frequency and colour of your wee is a good indicator of how hydrated you are. More water in leads to more water out, and therefore more toilet trips. A light straw colour is recommended. Anything darker, like orange or brown, you are dehydrated and need to drink more water! (https://www.healthline.com/health/hydration-chart) On the other end of the scale, clear wee means you have probably drunk too much water (see below).

Can I over hydrate?

Yes, you can. This occurs when you drink more water than your kidneys can remove from your urine. Endurance athletes, such as those who run marathons and triathlons, sometimes drink too much water before and during an event. In healthy people, athletes are at the highest risk for overhydration. (https://www.healthline.com/health/overhydration)

Further tips for running during hot weather

Lastly, when running in hot weather, please also consider:

• Taking stock of the conditions alongside your own capabilities, how you’re feeling on that particular day, and adjusting your goals where needed (this may mean running in a lower group for a club session, or lowering your pace on race day.

• Sports sunscreen (sweat / water resistant)

• Wearing a hat (sun stroke is no joke)

Stay safe, and HYDRATE!