How much magnesium do you lose working out? The surprising truth about exercise and mineral loss

October 11, 2025 •

4 min read

According to scientific research, athletes can experience a 10-30% increase in magnesium loss during intense exercise. Contrary to popular belief, the amount of magnesium you lose working out directly through sweat is minimal, with the most significant losses occurring indirectly through increased urinary excretion.

Quick Summary

Intense exercise primarily increases magnesium loss through urine, not sweat, as kidney function is reduced. This increases the magnesium requirements for active individuals, impacting energy metabolism, muscle function, and recovery if not properly managed through diet or supplementation.

Key Points

Indirect Loss: The majority of magnesium loss during exercise occurs through increased urinary excretion, not sweat, due to altered kidney function.
Increased Demand: Intense exercise raises the body's demand for magnesium by 10-30% compared to sedentary individuals.
Diet First: Maintaining a diet rich in leafy greens, nuts, seeds, and whole grains is the best way to ensure adequate magnesium intake.
Supplementation for Athletes: Supplements may be beneficial for active individuals who struggle to meet their higher magnesium needs through diet alone.
Recognize Deficiency: Signs of low magnesium include muscle cramps, fatigue, poor recovery, and difficulty sleeping.
Supplement Types Vary: Choose supplements based on bioavailability; forms like citrate and glycinate are better absorbed than oxide.
Individual Needs: Magnesium requirements vary based on activity level, age, gender, and overall health.

The Importance of Magnesium for an Active Body

Magnesium ($Mg^{2+}$) is a vital mineral involved in over 300 enzymatic reactions in the human body, making it crucial for virtually all physiological functions, especially for those who are physically active. It plays a critical role in energy production, helping to convert food into energy by activating adenosine triphosphate (ATP), the body's primary energy currency. For muscles, magnesium is essential for contraction and relaxation, while also supporting nerve function and bone health. Its role extends to regulating blood glucose levels, protein synthesis, and even blood pressure. An optimal magnesium status can enhance performance, reduce muscle damage, and aid in quicker recovery for athletes.

The Science of Magnesium Loss During Exercise

Sweat vs. Urine: The Real Culprit

While many assume that vigorous exercise and heavy sweating are the main pathways for magnesium loss, research reveals a more nuanced picture. The magnesium concentration in sweat is surprisingly low, with studies showing an estimated loss of only about 2 mg per hour. However, this does not mean exercise has no effect on your magnesium levels. The primary mechanism for increased magnesium loss during physical activity is through the kidneys.

During exercise, blood flow is redirected away from the kidneys and towards the working muscles. This change reduces kidney function and increases the amount of magnesium excreted in the urine. This leads to an average increase in magnesium loss of 20-30% for athletes, making urinary excretion the most significant factor in exercise-induced depletion. This increased excretion is the body's response to the heightened metabolic demand and stress placed on the system during physical exertion.

Factors Influencing Depletion

Several factors can influence the rate and amount of magnesium lost during a workout, including:

Exercise intensity and duration: The more intense and prolonged the exercise, the greater the metabolic demand and the higher the rate of urinary magnesium excretion.
Environmental conditions: Exercising in hot and humid conditions leads to higher sweat rates, though this contributes less to magnesium loss than urinary excretion. However, the combined effect is significant for maintaining overall electrolyte balance.
Hydration status: Dehydration can exacerbate electrolyte imbalances, though research indicates sodium is a more critical electrolyte lost through sweat.
Individual physiology: Factors like body size, age, gender, and baseline magnesium status can all play a role in an individual's specific needs and losses. Female athletes, particularly during the follicular phase of their cycle, may also experience hormonal fluctuations that influence magnesium availability.

Recognizing the Signs of Magnesium Deficiency

For athletes and active individuals, recognizing the signs of suboptimal magnesium levels is important to prevent adverse effects on performance and health. Symptoms can include:

Muscle cramps and spasms: Uncontrolled muscle tension or twitching can be a sign of low magnesium, which helps muscles relax after contraction.
Fatigue and weakness: Magnesium is essential for energy production. A deficiency can lead to feelings of low energy and poor endurance.
Poor sleep quality: Magnesium has calming properties that can help regulate the nervous system and sleep-wake cycle.
Poor recovery from workouts: Inadequate magnesium levels can increase muscle damage and oxidative stress following intense exercise, hindering recovery.
Anxiety and irritability: Magnesium helps regulate the body's stress response, and low levels can negatively impact mood.

Replenishing Magnesium: Dietary Intake and Supplementation

The best way to maintain optimal magnesium levels is through a balanced diet rich in magnesium-containing foods. For active individuals with higher needs, incorporating specific foods and potentially supplements is important.

Magnesium-Rich Foods

Leafy greens: Spinach and kale are excellent sources.
Nuts and Seeds: Pumpkin seeds, chia seeds, and almonds are particularly high in magnesium.
Legumes: Black beans, edamame, and lentils provide a good amount of the mineral.
Whole Grains: Brown rice and whole wheat bread offer more magnesium than their refined counterparts.
Dark Chocolate: Unsweetened cocoa powder and dark chocolate with high cocoa content are rich sources.
Avocados: This fruit is a good source of magnesium and healthy fats.

Magnesium Supplement Comparison

For those with higher athletic demands or dietary gaps, a supplement may be necessary. Different forms of magnesium have varying levels of bioavailability and specific uses.


Magnesium Form	Bioavailability	Common Uses
Magnesium Citrate	High	General supplementation, often used for digestive health as it has a laxative effect.
Magnesium Glycinate	High	Supports relaxation, improved sleep, and muscle recovery. Often preferred for individuals sensitive to the laxative effects of other forms.
Magnesium Oxide	Low	Low absorption rate, frequently used as a laxative. Not ideal for correcting a systemic deficiency.
Magnesium Malate	Good	Supports energy production and muscle function, potentially aiding in combating fatigue.

Conclusion

While the amount of magnesium you lose working out through sweat is minimal, the stress of intense exercise increases the body's overall magnesium requirements, leading to greater losses through urine. Active individuals, particularly athletes, should be mindful of their magnesium intake to avoid deficiency, which can compromise energy production, muscle function, and overall athletic performance. By prioritizing a diet rich in magnesium-rich foods and considering a high-bioavailability supplement if needed, you can maintain optimal levels. Consulting with a healthcare provider or dietitian can help determine if supplementation is appropriate for your specific needs, supporting peak performance and recovery.

Optional Outbound Link: For more detailed information on dietary reference intakes for magnesium, visit the National Institutes of Health (NIH) Office of Dietary Supplements website.

Frequently Asked Questions

Scientific evidence indicates that the amount of magnesium lost directly through sweat is minimal, estimated at only about 2 mg per hour.

During intense physical activity, blood flow is diverted from the kidneys, reducing their efficiency. This causes an increase in urinary magnesium excretion, which is the main source of exercise-induced magnesium loss.

While an active lifestyle increases magnesium demands, not all individuals require a supplement. A well-balanced diet with magnesium-rich foods can often meet the needs of those with moderate activity levels. Supplements are generally recommended for elite athletes, those with low baseline levels, or specific dietary restrictions.

Excellent food sources include leafy green vegetables like spinach, nuts and seeds (pumpkin, chia, almonds), legumes, whole grains, avocados, and dark chocolate.

Some studies have linked low magnesium to muscle cramps, and supplementation is a common remedy. However, scientific evidence on its effectiveness for exercise-associated muscle cramps is limited and inconsistent, with some research suggesting cramps are more related to nerve function or other electrolytes like sodium.

Highly bioavailable forms of magnesium, which are absorbed more completely by the body, include magnesium citrate and magnesium glycinate. Magnesium oxide, though common, is poorly absorbed.

Assessing magnesium levels can be difficult as only a small percentage is in the blood. However, symptoms of deficiency can include muscle cramps, fatigue, poor sleep, and reduced athletic performance. A blood test, particularly an RBC magnesium test, may offer a better indication of status.