Vitamin D für Sportler - ein neuer Blickwinkel

Vitamin D is synthesized in the skin upon exposure to ultraviolet B (UVB) radiation, hence it is often referred to as the sunshine vitamin. It is classified as a fat-soluble vitamin, although in reality it is a prohormone, a substance that can be converted into a hormone. The active form of vitamin D collaborates with parathyroid hormone and calcitonin to regulate the concentration of calcium and phosphorus in the plasma. Vitamin D can amplify the absorption of these minerals in the gut, contributing to bone mineralization and protecting against the consequences of osteoporosis and osteopenia, as well as fractures associated with stress. Vitamin D sourced from food, supplements, and UVB exposure must undergo two chemical processes before becoming usable by the body. Initially, vitamin D is metabolized in the liver into 25-hydroxyvitamin D [25(OH)D], also known as calcidiol, and subsequently forms the physiologically active complex 1,25-dihydroxyvitamin D [1,25(OH)2D], commonly known as calcitriol. Calcitriol, as a steroid hormone, regulates over 50 genes in various tissues of our body, including muscles and nerves.

Before the connection between UVB radiation and the synthesis of vitamin D was established, sunlight was considered a source of physical strength and vitality. Ancient Egyptians perceived the sun god Amon-Ra as the one who could make one man stronger than the entire crowd. However, ancient Olympians were instructed to train and live in the sun. Nowadays, due to gymnastics and office work, we generally have low levels of vitamin D in circulation. Currently, we distinguish four possible levels indicating the status of the supply of the mentioned vitamin D: – deficiency level (less than 30 nmol/L); – suboptimal levels (30–50 nmol/L); – adequate levels (50–125 nmol/L); – high levels (more than 125 nmol/L). This is a classification that does not take into account the special needs of physically active people. In 2006, Professor Heike A. Bischoff-Ferrari presented a better classification, stating that the optimal range for muscle function is 90–100 nmol/L. Too many athletes show a vitamin D content in the body that is unsatisfactory in terms of effectiveness. One study discovered that an alarmingly large number of athletes have suboptimal vitamin D levels: 94% of dancers, 94% of basketball players, and 67% of taekwondo athletes. Although there are few studies confirming the impact of supplementation on the effectiveness of young athletes, they are still promising. For example, a study from 2012 showed that 5000 IU of vitamin D3 over an 8-week period significantly increased the 25(OH)D levels in athletes, resulting in a significant improvement in their sprinting and high jump performance.

Vitamin D can be found in food products such as eggs, salmon, and potatoes, as well as in supplements. The standard variant is vitamin D3, which is better absorbed than other calcitriol precursors. The need for vitamin D should be determined individually, taking into account its status in the body. Generally, it is recommended to take 2000 IU per day, although some people use it at higher doses. Vitamin D is fat-soluble, which can lead to difficulty in excreting excess, compared to water-soluble vitamins. This is due to its fat solubility, which means that it is best absorbed in the presence of fats. Studies have shown that the absorption of vitamin D from a meal with 11 grams of fat is greater than from a meal with 35 or 0 grams of fat.