How The Environment and Too Much Salt Affect Sweat Rate
We wrote a pretty extensive blog on hydration in 2018 after the carnage of Ironman Boulder. If you haven’t read it yet, we suggest you give it a look HERE. After the 2019 Ironman Texas (14% Did Not Finish rate), we revisited this topic with a focus on how the environment, and specifically acclimatization affect our sweat rate and sodium needs.
January through early May are typically cool and wet, but as soon as race season hits in late May, the temp seems to skyrocket. This causes extra stress on the body due to our lack of acclimatization (fancy word for saying we aren’t accustomed to the environment). This lack of acclimatization will severely impact your sweat rate and electrolyte losses. Going from a cool climate, or at sea level to a hot climate or altitude can cause an increase in both your sweat rate and sodium losses. Just how much of an increase? Honestly, we don’t know for sure. Generally speaking, your sweat rate will increase by around 5 – 10%, depending on the intensity, and sodium loss will increase by around 200 – 400mg per hour.
So does that mean we can just dump more sodium in our bottles or lick some more sea salt? Definitely not! We talk a lot about the reasons why this is not the best approach in the hydration blog so we will not cover that here. Instead, we will focus a bit on what happens internally when you consume too much sodium.
Our bodies love homeostasis (fancy word for balance). They are super smart machines that will do whatever it takes to maintain an optimal environment. They are so smart that they will actually recycle waste products for use. As we sweat, our bodies want to reabsorb both water and sodium as long as the balance of the environment is correct.
Our bodies reabsorb sodium via 2 main mechanisms. We are going to do our best to highlight what this means for athletes, but this will cause us to leave a lot of stuff out as it doesn’t have a true bearing for the athlete. Just know there is a lot more going on than what we describe.
The first mechanism where the majority of sodium is reabsorbed transports one water molecule and one sodium molecule. This mechanism is driven solely by the sodium to potassium ratio of your intracellular fluid. This means if you consume too much sodium, your body will start dumping it out to bring your sodium to potassium levels within a normal range. This will, in turn, concentrate your sweat with sodium and your body will not reabsorb either the water or the sodium due to an imbalance of osmolality.
This leads to the second mechanism of sodium reabsorption. At this point, sodium, chloride and potassium are reabsorbed. This mechanism, like the first, is driven by the sodium to potassium ratio. There are a couple of things that can affect sodium reabsorption. If you overload your body with sodium and/or chloride, your body will not be able to reabsorb the sodium. If this happens, you force your body to secrete stored water to flush out the extra sodium and chloride. Essentially you dehydrate your body.
So what’s the answer? We’ve found that consuming 750 – 1,000 mg of sodium per liter of fluid (about 33 ounces) reduces urine output and increases hydration. This has confirmed our recommendations in the hydration blog above. Just be aware, there is a point of diminishing return so more sodium is not the answer.
On a side note, we have found that loading the body with bicarbonate does help with both sodium and water reabsorption which may be another reason NBS Preload works so well.