The Hydration Debate - How Much Water Do You Really Need?

We explore whether there is a danger to drinking too much water and if it is better for you to drink when you’re thirsty, rather than aiming for a daily quota.

Regardless if you’re an experienced runner, athlete or novice, you’ve likely been reminded by your coach or peers make sure you drink enough water during your run!” 

For years the recommendation from coaches has been to drink before you are thirsty, to prevent dehydration and subsequent decrements in performance. But if you aren’t racing at the front of the pack, or competing professionally, do you need this much water? 

Hydration is currently a hot topic and it’s divided into two main camps: the traditional camp who believes you should pre-hydrate by drinking 8 cups of water daily, versus a growing camp who believes you should only drink when thirsty. It can be a complicated topic, especially when the men and women in white lab coats can’t even agree on the best strategy. So, what are the best guidelines for you? 

The Recommended Guidelines #

The American College of Sports Medicine’s (ACSM) recommendation for endurance athletes is to consume 5 – 7ml water per kilogram bodyweight in the four hours before exercise. This translates to approximately 340 – 477ml for a 150 lb. female and 455 – 636ml for a 200 lb. male. The general recommendation is to drink until your urine is clear. This seems very reasonable, so why the sudden change in thinking? 

Unfortunately, it’s not quite that straightforward. Just because you drink water doesn’t mean you’re absorbing the water. The composition of the water largely determines how much you absorb. If you drink distilled water with no salt, you won’t absorb the water and you’ll begin to deplete your blood sodium levels leading to hyponatremia. 

The Dangers of Too Much Water #

Hyponatremia sets in when the fluids you consume are greater than the amount of fluids you lose via sweat. Common symptoms of hyponatremia include nausea, muscle weakness, and disorientation, which can be easily confused with symptoms of dehydration. The problem becomes dangerous if you give a person suffering from hypoatremia more water. Increased water will further dilute their blood sodium levels which can lead to cerebral edema, pulmonary edema, and death. 

When a Boston marathoner died of hyponatremia in 2002 the wheels were put into motion to find the answers behind what hydration strategy is safest for all athletes. This led to the recent drink to thirst” stance on hydration and a new set of recommendations. 

New Thinking — Drink to Thirst #

In fact, this new thinking goes all the way back to the early 1990s when a ground-breaking study was published by Dr Tim Noakes PhD and his colleagues regarding the potential danger of overconsuming water during exercise. Contrary to popular belief, they found drinking too much water was far more dangerous than not drinking enough. The body’s inherent mechanism to maintain hydration balance has since been shown to be more than enough to keep you hydrated and prevent the catastrophic effects of hyponatremia. This has led to changes in recent recommendations for endurance athletes to simply drink to thirst.” 

What isn’t Discussed — The Composition of Water #

The composition of your water – specifically the amount of salt and carbohydrates – plays a major role in hydration and your capacity to effectively absorb the water you are drinking. Just because you drink a lot of water, doesn’t mean you’re hydrated. If you pee just as much as you drink, you’re likely not making the most of your water intake. Many people can actually drink less and be more hydrated. 

As mentioned above, if you drink too much distilled water you’ll flush out sodium from your body, depleting blood sodium levels and leading to hyponatremia. Fear not, it’s very rare to die of hyponatremia, but if you’re an avid recreational exerciser (in particular female) it’s important to consider (elite level athletes are less prone to hyponatremia). 

Adding salt (and potentially carbohydrates) to your water helps to maximize absorption. Nature is very smart; the fructose in a piece of fruit is naturally surrounded in fibrous pectin, which leads to a gradual release of fructose for energy. In sports drinks, your gut receives a large bolus of fructose all at once which can slow gastric emptying rate or the speed at which food and liquids leave your stomach. Too much fructose, or too many sips from a sports drink can lead to bloating, discomfort, and subsequently poor performance. 

Gender Differences in Hydration #

Interestingly, there are differences between men and women when it comes to hydration. The female hormonal terrain is more complex than that of men, which impacts the hydration question. The research of Dr Stacey Sims PhD highlights that women are more susceptible to hyponatremia during their high hormonal phase – between ovulation and menses – than during their low hormonal phase. Furthermore, hormonal shifts in oestrogen as well as high stress (e.g. exercise) can alter vasopressin release, which decreases a woman’s thirst cue during the high hormonal phase. Fructose is also poorly absorbed in women compared to men, which can slow gastric emptying rate. 

How Should I Hydrate? #

Your hydration plan should depend not only on your gender, but your level of competition and general state of hydration. To stay hydrated away from competition, an ancestral diet is a great platform for maintaining hydration because it’s naturally high in animal protein, vegetables and fruits, which provide a wealth of water and electrolytes to help keep you hydrated. Naturally salty foods like oysters, mussels, sardines, cured meats, olives, etc are great additions to your nutritional arsenal. 

A general way to tell if you’re adequately hydrated is to look at the colour of your urine. If it’s completely clear, you are likely over-consuming water and over-hydrating. If your urine is a darker yellow colour, you likely need to increase you veggies and fruit consumption and add more water into your diet (Note – if you are taking a b‑vitamin supplement it will lead to a very bright yellow urine. This does not mean you’re dehydrated). A urinalysis test can help confirm your hydration status. 

The average exerciser likely does not sweat enough to warrant the ingestion of large amounts of water and the old refrain of having a cup of water at every drink station isn’t necessarily the best strategy. Don’t worry about passing over a few water stations at your next race, let thirst be your guide and simply drink if you feel thirsty. 

For elite runners, a useful strategy to determine your hydration plan is to weigh yourself before and after your run. If you’ve gained weight, then you’re definitely over-consuming and you need to dial back your water intake. If you lose more than 2% of your bodyweight, you need to bump up your intake. 

It’s great to see so many people being active and training to compete in 10k, half and full marathon events throughout the year. Listen to your body and pay attention to a few key metrics – bodyweight, urine colour, hormonal phase in females – to ensure you’re optimally hydrated to look, feel, and perform your best!