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Getting salty over heat stress

How does salt intake impact the human body when exercising in a high heat, low humidity environment? This study explored the issue.

Study under review: Impact of 3-day high and low dietary sodium intake on sodium status in response to exertional-heat stress: a double-blind randomized control trial.

Introduction

In the early 1900s, hydration was an afterthought in many forms of athletics and physical exercise. Ironically, it was viewed as weakness in marathons up until the 1960s and drinking anything other than liquor—yes, you read that correctly—was considered taboo. The winner of the 1896 Olympic marathon drank cognac and in 1908 at the Chicago Marathon, Albert Corey attributed his win to sipping on champagne throughout the race. Drinking alcoholic beverages wasn’t an unknown practice, and it has been used in the world of sport performance for some time.

The notion that drinking anything other than liquor would negatively affect race performance spawned from research showing that the runners who lost the most weight ran the fastest[2]. Some people took this to imply that drinking next to nothing would boost performance, since cutting liquid results in the biggest reductions in body mass. It wasn’t until the mid-to-late 1960s that researchers began to warn that the effects of inadequate water intake during marathon[2] running could be detrimental, and likely harmful, to race-day performances. Not long after, a team of scientists came together in 1965 at the University of Florida to develop one of the most iconic brands to date: Gatorade. This line of work birthed a new market of supplements: sports drinks.

A $22.37 billion industry, the market is saturated with various names claiming to have the perfect balance of electrolytes to rehydrate athletes better than their competitors. Gatorade pioneered this space into the behemoth it is today. Various ingredients are used to hydrate and balance the electrolytes within your body, from magnesium to potassium, as well as the primary ingredient discussed in this review: sodium chloride, more commonly known as table salt.

Given the mass amount of profit there is in promoting supplements geared toward hydration, it’s reasonable to be skeptical of any marketing ploy designed to sell more of them. But context is crucial, and it’s been shown in multiple studies that there is a benefit to keeping hydrated for health and performance purposes[3]. As such, hydration during exercise is just as critical as going into a training session well-hydrated. During exercise, there is a marked reduction in plasma volume from being slightly dehydrated[4]. This can cause a significant reduction in cardiac output and result in the athlete being more susceptible to fatigue[5] due to a lack of hydration. Fatigue’s relationship to dehydration is charted in Figure 1. In view of the performance impact this creates, it would be useful to find ways to maintain hydration.

The present study investigated the effects of three days of high, low, or habitual dietary sodium intakes on sodium balance and various physiological markers of stress before and during an endurance based exercise performed in a hot environment. The authors hypothesized that there would be a significant difference in dietary sodium intake, plasma, and sweat sodium concentrations between the conditions, with a minimal difference seen in hydration status and cardiovascular and thermoregulatory variables.

In the early 1900s, hydration was an afterthought in many forms of athletics and physical exercise. Now it’s a $22.37 billion industry, and proper hydration is one of the most critical factors when it comes to athletic performance. The study under review explores how dietary sodium intake affects measures of hydration status and cardiovascular and thermal variables.

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Other Articles in Issue #62 (December 2019)