Vitamin D and Magnesium: A Focused Review on Their Effects in Athletes

Paper: Dominguez, L.J. et al. (2025). The Importance of Vitamin D and Magnesium in Athletes. Nutrients. 17(10), 1655. https://doi.org/10.3390/nu17101655

In the realm of sports nutrition, vitamin D and magnesium have emerged as pivotal nutrients with multifaceted roles that extend beyond basic health maintenance to directly influencing athletic performance, recovery, and injury prevention. In this edition of Research Watch, we summarise the specific insights of Dominguez et al.'s comprehensive 2025 paper on the the particular effects of vitamin D and magnesium that are of paramount interest to athletes. Vitamin D’s influence in athletes transcends its classical role in calcium homeostasis and bone health, impacting muscle function, immune modulation, and potentially cardiovascular health. Central to its biological actions is the vitamin D receptor (VDR), expressed in diverse tissues including skeletal muscle, immune cells, and the brain.

I. Vitamin D

Vitamin D’s influence in athletes transcends its classical role in calcium homeostasis and bone health, impacting muscle function, immune modulation, and potentially cardiovascular health. Central to its biological actions is the vitamin D receptor (VDR), expressed in diverse tissues including skeletal muscle, immune cells, and the brain.

Muscle Function: Vitamin D deficiency commonly manifests as muscle weakness, which is detrimental to athletic performance. The active form, calcitriol (1,25(OH)2D), activates VDR in muscle cells, promoting genomic and non-genomic pathways that enhance muscle cell growth, particularly of type II fibers critical for strength and speed. Experimental models demonstrate that vitamin D stimulates myogenic differentiation, increases myosin heavy chain expression, and supports calcium regulation essential for muscle contraction. VDR knockout models reveal decreased muscle strength and fiber size, underscoring vitamin D’s role in muscle integrity. Clinically, higher pre-exercise serum 25(OH)D correlates with reduced post-exercise muscle weakness and faster recovery, although supplementation trials yield mixed results likely due to heterogeneity in baseline vitamin D status and dosing.

Bone Health and Stress Fractures: Vitamin D enhances intestinal absorption of calcium, phosphate, and magnesium, thereby supporting bone mineralization and remodeling. Its regulatory interaction with parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) maintains mineral homeostasis critical for skeletal strength. Stress fractures, prevalent in athletes (notably runners and track and field participants), are associated with low serum 25(OH)D levels (<20 ng/mL). Supplementation studies, including randomized controlled trials (RCTs) in military recruits and young athletes, demonstrate a reduction in stress fracture incidence and improved bone density metrics. These findings highlight the necessity of maintaining sufficient vitamin D status to prevent skeletal injuries that compromise athletic longevity.

Cardiovascular and Respiratory Systems: Although the cardiovascular effects of vitamin D in athletes remain inconclusive, deficiency is linked to impaired cardiac adaptation to training. More robust evidence supports vitamin D’s role in respiratory health; deficiency increases susceptibility to upper respiratory tract infections (URTIs) and asthma exacerbations, conditions that significantly impact athlete performance and training consistency. Maintaining serum 25(OH)D above 30-38 ng/mL appears protective, with supplementation reducing infection risk, particularly in winter or low UVB environments.

II. Magnesium

Magnesium’s indispensable role in athletic physiology stems from its involvement in over 600 enzymatic reactions, particularly those related to energy metabolism and neuromuscular function. Its dynamic interaction with ATP, forming the biologically active Mg-ATP complex, is fundamental for muscle contraction, relaxation, and overall cellular energetics. 

Muscle Function: Magnesium modulates muscle contraction by regulating calcium influx and supporting mitochondrial function. Approximately one-third of muscle magnesium resides in mitochondria, facilitating oxidative phosphorylation and ATP synthesis. Deficiency impairs mitochondrial efficiency, elevates oxidative stress, and reduces aerobic capacity, which can lead to premature muscle fatigue and decreased endurance. Magnesium also activates glycolytic enzymes and stabilizes ion channels crucial for neuromuscular excitability. While supplementation studies show mixed effects on performance, positive outcomes are noted primarily when base levels were suboptimal, emphasizing the need for individualized assessment.

Bone Health: Magnesium deficiency is linked to decreased bone mineral density (BMD) through increased osteoclast activity and impaired osteoblast function. Epidemiological data associate higher magnesium intake with improved BMD and potentially reduced fracture risk, although definitive evidence in athletes is limited. Given the high physical demands and risk of bone stress injuries in athletes, ensuring adequate magnesium intake is vital for skeletal integrity. 

Cardiovascular Health: Magnesium acts as a natural calcium antagonist, promoting coronary vasodilation and preventing arrhythmias by stabilizing cardiac ion channels and reducing inflammation. Athletes, especially endurance athletes, risk hypomagnesemia due to sweat losses, which can increase sudden cardiac death risk. Maintaining sufficient magnesium levels is essential for preventing cardiac arrhythmias and supporting vascular function.

Respiratory Function: Magnesium’s bronchodilatory effects, mediated by calcium channel blockade and modulation of inflammatory responses, are beneficial in managing exercise-induced bronchoconstriction and asthma—conditions prevalent in elite athletes. Magnesium supplementation has demonstrated efficacy in acute asthma management, although studies specifically targeting athletes remain scarce.

III. Interactions and Practical Implications

Vitamin D and magnesium share a synergistic relationship critical for metabolic and physiological functions in athletes. Magnesium is essential for vitamin D synthesis, transport, and activation, while vitamin D enhances magnesium absorption. Deficiencies in magnesium can impair vitamin D metabolism, exacerbating musculoskeletal and immune dysfunction. This interdependence underscores the importance of concurrent monitoring and optimization of both nutrients.

For athletes, maintaining adequate vitamin D and magnesium status is fundamental to optimizing muscle function, bone health, cardiovascular stability, and immune resilience. While evidence on direct performance enhancement from supplementation remains inconclusive, preventing deficiencies mitigates injury risk, supports recovery, and sustains overall athletic health. Personalized nutritional strategies, routine monitoring, and targeted supplementation in at-risk athletes—such as those training indoors, with darker skin, or at high latitudes—are prudent measures grounded in current scientific understanding.

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