While low-sodium diets are often recommended for the general population to combat hypertension, these guidelines may not be suitable or even healthy for athletes. Athletes, due to their increased physical activity and sweat production, have unique sodium requirements. This article delves into the complexities of sodium intake for athletes, providing guidelines for maintaining optimal performance and health.
Understanding Sodium's Role in the Body
Sodium, an essential mineral, plays a vital role in numerous bodily functions, including:
- Fluid Balance: Sodium controls fluid balance in our bodies and maintains blood volume and blood pressure. It is the main cation in extracellular fluid, contributing to the release of digestive secretions and controlling the absorption of certain nutrients like amino acids, glucose, galactose, and water.
- Nerve and Muscle Function: It is vital for the stimulation of muscle and nerve cells.
- Blood Pressure Regulation: Sodium ensures sufficient blood volume, blood pressure and, ultimately, organ perfusion.
- Acid-Base Balance: Sodium is also involved in the control of the acid-base balance.
For athletes, sodium is crucial in maintaining serum electrolyte concentrations, resulting in a balance of intravascular osmotic pressure and plasma volume. It increases the thirst stimulus and reduces the amount of urine produced, effects that ultimately reduce physical fatigue and medical problems associated with these homeostatic imbalances in endurance sports.
The Sodium-Hypertension Link: A Closer Look
Consumption of Sodium Chloride (NaCl) has been linked with a rise in cases of hypertension, or high blood pressure, in the population at large. Because hypertension is a huge risk factor in all manner of nasty cardiovascular diseases, salt has, by association, taken a great deal of flak for its alleged contribution to this growing issue. In direct response, government guidelines in most countries, including the UK and USA, currently recommend very low daily salt intake levels (typically between 2000mg and 2500mg of sodium; salt is ~40% sodium so this equates to roughly 6g per day). The American Heart Association even goes so far as to suggest a target intake of under 1500mg of sodium a day for optimal health (3.75g salt per day).
As you consume more and more salt, your body tends to retain more and more fluid in the blood to maintain acceptable blood sodium concentrations. This has the effect of expanding total blood volume and therefore acutely increasing blood pressure (i.e., elevating BP in the short term).
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While there’s no debating that this acute effect of salt consumption on blood pressure is real, the link between sodium intake and chronic (long-term) hypertension is potentially a lot more complex, and has been the subject of growing debate in recent years. Many people with high blood pressure actually don’t respond well to a low-sodium diet, and many people who eat a high-salt diet don’t end up with hypertension.
Data published in 2017 from a 16-year study of blood pressure in a group of 2600 Americans seems to agree with DiNicolantonio, as they showed an INCREASE in blood pressure in those who routinely consumed less than 2500mg of sodium per day when compared with their peers who consumed more. While the exact mechanisms causing these findings are likely to be pretty complex and require further investigation, the overall message seems both clear and plausible: too little sodium in the diet is likely to be as damaging as too much. As a result, the conversation on sodium and blood pressure needs to start to shift to looking at what is optimal, rather than simply striving to promote arbitrary, universal upper limits for consumption, which has been the trend to this point in time.
Why Athletes Need More Sodium
While cutting back on overall sodium in the diet may be sound advice for the sedentary public, athletes have a special need to replenish lost sodium stores. Athletes need more sodium because they lose more sodium in sweat. The range of sodium lost in the sweat of athletes is large because some athletes are salty sweaters and others are not. Sweat is saltier during the early stages of training and heat acclimation than after an athlete is fit and fully acclimated to exercise in the heat.
The ‘average’ (read ‘non-exercising’) person may only require ~2000mg or less of sodium per day to meet their basic physiological needs. The average Western diet allegedly contains about 3,400mg/day, so it’s easy to see why most folks are able to meet and exceed this without even thinking about it. It’s also easy to see why general guidelines to reduce sodium intake might not be completely misguided, as many people are probably routinely consuming quite a bit more than they need.
But what about the athletes? The average liter of human sweat contains ~1000mg sodium (range ~200mg/l - 2000mg/l) and sweat rates easily reach 1.5-2 litres per hour in trained athletes, so it’s very easy for some of us doing multiple hours of exercise a day, on multiple days of the week, to rack up some significant sodium (and fluid) losses compared with the rest of the population. These losses can far exceed the 2500mg or even 3400mg/day that are recommended or consumed in a ‘normal’ diet.
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This is especially true for anyone with exceptionally high rates of fluid and sodium loss, or anyone doing sports that demand hours and hours of practice or training on back-to-back days. As someone with both salty sweat (I lose around 1800mg/l) and a high sweat rate (2l per hour in hot conditions), I can lose 6-8g of sodium in a hard two-hour run. In the past, I learned the hard way that taking insufficient sodium in and around exercise left me performing poorly and feeling terrible. For an athlete like me, trying to get by on the recommended 2000mg/day would be far from optimal for health or performance. An excellent paper looking at the role of sodium in the diet of athletes summarizes the topic neatly. It points out that there’s been a widespread acceptance of the fact that athletes who sweat a lot need more fluid than the average person, but there’s been much less emphasis placed on them potentially needing a lot more sodium too - probably because it contradicts the perceived wisdom that sodium is ‘bad’ for you.
Another fascinating case study focused on an athlete in Germany who suffered over-training type symptoms (and increased blood pressure) when undertaking regular endurance training. At the time, she was following a low sodium diet that she perceived to be ‘healthy,’ and was able to reverse her condition simply by increasing dietary sodium intake - avoiding the usual decrease in training load that is normally required to correct symptoms of over-training syndrome.
This is consistent with a host of anecdotal reports we’ve had from athletes over the years who’ve attempted to follow ‘best practice’ by eating low sodium while simultaneously training hard and losing a lot of sodium in their sweat.
Risks of Sodium Imbalance in Athletes
Hyponatremia
While sodium is essential, excessive fluid consumption, especially without adequate sodium intake, can lead to hyponatremia, a condition characterized by a low blood sodium concentration (less than 135 mmol/L). This is most often seen in endurance exercise, such as in marathons and triathlons.
Causes:
- Excessive fluid consumption during exercise
- Increased sodium loss in sweat
- Loss of normal Antidiuretic hormone (ADH) suppression, called the syndrome of inappropriate ADH secretion (SIADH)
Symptoms:
Symptoms of hyponatremia vary, including nausea, headache, confusion, and in severe cases, seizures and coma. Because some symptoms of hyponatremia can be identified with other conditions, the clinical sign that differentiates hyponatremia from other conditions that result in collapse is vomiting. Vomiting may be a reflex action in response to the increasing distension of large and unnecessary amounts of fluid within the gastrointestinal tract or may be caused by the central nervous system.
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Prevention:
EAH can be prevented by avoiding over-hydration, ensuring adequate oral sodium intake and training athletes, focusing on sweat rate and sweat sodium content, exercise intensity and environmental conditions . Estimates of individual athlete replacement needs can also be used by monitoring weight changes during training activities, although this may not be practical. Forced hydration, particularly in large quantities, should be discouraged.
Exercise-Associated Muscle Cramps (EAMC)
Exercise-associated muscle cramps (EAMC) are defined as painful, spasmodic and involuntary contractions of skeletal muscles during or immediately after physical activity. The basic etiological evidence in the literature is that electrolyte depletion through excessive sodium loss in sweat along with dehydration causes this condition.
Determining Individual Sodium Needs
The range of individual sweat sodium losses during exercise is extremely large. As is the case with daily water needs, daily sodium needs can also vary widely, especially for athletes, workers, and soldiers -in other words, anyone who sweats profusely. For sedentary individuals, the primary route of sodium loss is via the urine. The kidneys can either conserve sodium if sodium intake falls below needs or can excrete sodium whenever intake exceeds needs. The latter scenario is virtually always the case with sedentary people.
Given the variability in sodium losses through sweat, it's crucial for athletes to determine their individual needs. Several factors influence sodium loss:
- Sweat Rate: The volume of sweat produced during exercise.
- Sweat Sodium Concentration: The amount of sodium present in sweat (can vary significantly between individuals).
- Acclimatization: Athletes who are acclimatized to the heat lose less sodium in their sweat.
- Exercise Intensity and Duration: Longer and more intense workouts lead to greater sodium losses.
Practical Assessment:
The most easily accomplished way to assess sodium needs is by having athletes weigh themselves before and after an exercise bout. Weight loss indicates the presence of dehydration and the need to increase fluid intake during future exercise bouts. Weight gain is a signal to drink less.
Practical Guidelines for Athletes
- Don't Rely Solely on Thirst: Thirst alone is not the best indicator of dehydration or the body's need for fluid, a fact that is particularly true during exercise. Both the American College of Sports Medicine (ACSM) and the National Athletic Trainers' Association (NATA) issued press releases soon after the IOM report, cautioning physically active people against "letting their thirst guide them." Rather, the clear and important health message should be that thirst alone is not the best indicator of dehydration or the body's need for fluid, a fact that is particularly true during exercise.
- Hydrate Adequately: The volume of fluid consumed by athletes during and especially after exercise should be based on the volume of fluid lost in sweat. The recommended fluid intake can be estimated as the difference between the athlete's body weight before and after activity. To minimize the potential for heat exhaustion and other forms of heat illness, ACSM and NATA experts recommend that water losses due to sweating during exercise be replaced at a rate close to or equal to the sweat rate.
- Choose Sodium-Rich Sports Drinks: Water and sports drinks are not dangerous to athletes when consumed as recommended -in volumes approximating sweat losses. Water quenches the sensation of thirst before body fluid replacement is achieved, so thirst should not be the only determinant of how much fluid is consumed under such conditions. Consuming a sports drink with adequate sodium (at least 100 mg/8 oz) encourages continued drinking, more adequately replacing the active individual's fluid and electrolyte needs.
- Consider Sodium Supplementation: For athletes with high sweat rates or those training in hot and humid conditions, sodium supplementation may be necessary to replenish lost sodium stores.
- Monitor Urine Color: Athletes engaged in vigorous training accompanied by profuse sweating should record body weights after urinating each morning and monitor the color of the urine. If body weight has dropped by more than 1 pound (about 0.5 kg) from the day before and if urine color is more like apple juice than lemonade, dehydration is likely and the athlete should pay extra attention to fluid intake during the day.
- Listen to Your Body: Pay attention to how your body feels during and after exercise. Symptoms like muscle cramps, fatigue, and nausea can indicate sodium imbalances.
Dietary Sources of Sodium
While sports drinks can be a convenient source of sodium during exercise, athletes should also focus on incorporating sodium-rich foods into their daily diet. Good sources of sodium include:
- Table salt
- Processed foods (in moderation)
- Canned soups
- Salty snacks (crackers, pretzels)
- Pickled foods
The Importance of Individualized Strategies
The bottom line on sodium intake for athletes (or anyone who sweats a lot during the course of their day) is that you should strive to be roughly in-line with your individual sodium losses as a minimum. To use an analogy from the field of Game Theory, sodium consumption should ideally be a zero-sum gain. Intake should essentially cancel out output and therefore, in theory, the effect on overall sodium balance (and as a result, blood pressure and other homeostatic measurements) should be net-zero.
And if Dr. DiNicolantonio is to be believed, then even taking in a little bit more sodium than you need ought to be fine, because the body can deal with a degree of excess relatively easily (assuming the kidneys are functioning well) and avoid any risk of incurring a deficit over time.
The 2004 recommendations on water and sodium intake from the Institute of Medicine (IOM) of the National Academy of Sciences are targeted primarily at sedentary Americans. These guidelines for water and salt intake should not be applied to athletes. The volume of fluid consumed by athletes during and especially after exercise should be based on the volume of fluid lost in sweat. The recommended fluid intake can be estimated as the difference between the athlete's body weight before and after activity.