## 3 Importance of Vitamin and Mineral Supplements
### Minerals  
Minerals, similar to vitamins, are essential micronutrients required in the diet of combat players and are classified into major and trace minerals (Figure 1) depending on the amount necessary for the body.  
_Calcium_, the most important mineral of the skeleton, is also involved in muscle contraction, heart rhythm regulation, coagulation and nerve conduction. Being involved in such important processes, calcium homeostasis is precisely regulated by calcitonin, parathyroid hormone and vitamin D. In a situation where the calcium balance is negative, the plastic concentrations are maintained within their required limits by mobilizing bone calcium. This fact has to be taken into consideration in athlete nutrition because proper bone mineralization is essential in fracture prevention. Calcium in combination with vitamin D was proven to increase bone mineralization and reduce fractures in a prospective study among female athletes. Although, in most cases, vitamin D is the limiting factor of bone mineralization and calcium uptake, proper calcium intake has to be taken into consideration, especially in calorie-restricted or dissociated diets, which are popular among athletes.  
_Magnesium_ is essential in sports nutrition, as it is utilized as a cofactor in over 300 enzymatic reactions, including those of ATP synthesis and muscle contraction [130]. Glucose metabolism is limited by magnesium availability, with magnesium being involved in glucose utilization and homeostasis, phosphorylation, pyruvate dehydrogenase and creatine kinase reactions [105]. Magnesium is demonstrated to promote muscle synthesis through activation of the mTOR pathway [106]. Magnesium might have a lifesaving role in sports due to its demonstrated arrhythmia prevention effects [131], given that most sudden cardiac deaths in athletes occur through arrhythmias [132]. Multiple studies have proved the efficiency of magnesium in sports related performance, such as increases in muscle strength and walking and running speed and a decrease in lactate levels [105].  
Higher training adaptation regarding erythrocyte and hemoglobin levels was observed in teakwondo athletes after magnesium supplementation [133]. In judo athletes, magnesium was demonstrated to reduce strength loss after a caloric restriction program [134].  
_Sodium_ is an important consideration because, during intense training, especially on hot days, large amounts of water and sodium are lost through perspiration [109; 135], so nutrition strategies for athletes should include sodium in foods and beverages in order to minimize diuresis, thus promoting regeneration in post-training athletes [114]. In the case of intense exercises that cause considerable sodium loss through sweating, sodium intake can exceed 10 g/day.  
_Iron_ deficiency in athletes can affect muscle function and limit work capacity, resulting in impaired athletic performance [123]. The causes that lead to a low iron status are low intake of heme food, inadequate energy intake, rapid growth of the player, training at high altitudes or intense training [123]. Iron supplementation is not recommended to occur immediately after intense training, as high levels of hepcidin may interfere with iron absorption [123; 136]. It is preferable for athletes to take in iron from food, especially by eating heme iron foods or combining non-heme iron foods with vitamin C foods for better absorption.