What do you know about Vitamin D?
Good morning, Vibers! Today we bring you a new blog to introduce a very special nutrient: vitamin D. Vitamin D is a crucial nutrient not only for general health but also for athletic performance. Deficiency in this vitamin is a serious issue in general internal medicine, and certain disorders have been linked to low levels of vitamin D. Certain populations, such as infants, children, premenopausal women, and the elderly, are at higher risk of developing osteoporosis and osteoporotic fractures, among other problems. For athletes, especially women, there may be an increased risk of vitamin D deficiency. Therefore, it is vital to understand how this vitamin works and how to obtain it. Keep reading to learn more:
What is Vitamin D?
Vitamin D is an essential fat-soluble vitamin. In addition to being obtained from dietary sources, the body can also synthesize it from exposure to sunlight (1). The two main forms of vitamin D are D2 (ergocalciferol) and D3 (cholecalciferol). Ergocalciferol can be obtained from plant sources, while cholecalciferol is found in animal products and produced in the skin upon exposure to sunlight. In the skin, under ultraviolet solar radiation, 7-dehydrocholesterol is converted into previtamin D3, which is then converted into vitamin D (2). Although the two main forms of vitamin D differ in the structure of their side chains, they do not differ in their overall metabolism or functions in the body. The metabolism of this vitamin converts both D2 and D3 into the biologically active form, calcitriol.
The serum concentration of calcidiol (the precursor of calcitriol) is the best indicator of vitamin D status, as it has a half-life of 15 days. An intake of 1,000 IU of vitamin D per day can increase blood levels by approximately 5 ng/ml. Although the exact levels of calcidiol needed for good health are unknown, levels below 10 ng/ml are associated with more severe deficiency diseases, such as rickets in infants and children, and osteomalacia in adults. Generally, a concentration above 15 ng/ml is considered adequate for good health (3).
Functions of Vitamin D
Vitamin D is an important hormone with a wide range of functions. Its main role is to regulate calcium homeostasis along with parathyroid hormone, which is essential for bone development and growth (4). Secondary biological actions of vitamin D metabolites include regulating immune function and protein synthesis (3).
Moreover, vitamin D is estimated to regulate the expression of over 1,000 different genes in the human body, accounting for 5% of the entire genome that codes for proteins. Vitamin D deficiency has been shown to impair muscle function, cause sarcopenia, and reduce muscle strength (5).
Vitamin D acts through vitamin D receptors (VDRs), and the expression of VDRs in skeletal muscle has been reported. Through these muscle fiber receptors, vitamin D can regulate serum calcium concentrations, directly impacting muscle contraction (6).
How to increase Vitamin D levels
1. Sun exposure
About 15-20 minutes of sun exposure without protection is sufficient to achieve adequate levels. However, the amount of sun needed to meet vitamin D requirements can vary depending on factors like skin color, time spent in the sun, weather conditions, latitude, altitude, season, time of day, sunscreen use, and clothing type.
☀️ To achieve adequate levels of Vitamin D, about 15-20 minutes of sun exposure without protection is sufficient.
2. Foods rich in vitamin D
Very few foods naturally contain this vitamin.
- Fatty fish, such as trout, salmon, tuna, and mackerel, as well as fish liver oils, are among the best natural sources of vitamin D.
- Beef liver, egg yolks, and cheese contain small amounts of vitamin D.
- Mushrooms provide some vitamin D.
- Fortified milks and cereals.
3. Supplementation
Over-the-counter vitamin D supplements contain either vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol). These compounds are processed by your liver and kidneys to create the active form of the vitamin (calcitriol).
- Vitamin D3 (cholecalciferol): This molecule is found in animal products and synthesized in the skin after sun exposure. It is the most bioavailable form and is the primary recommendation when choosing a vitamin D product. It is not suitable for vegans or vegetarians due to its animal origin.
- Vitamin D2 (ergocalciferol): This compound is found in mushrooms and plant-based foods. Therefore, D2 supplements are suitable for vegans and vegetarians. However, this form is less well-absorbed and stored compared to vitamin D3. It is recommended for those following a strict vegetarian diet.
Conclusions
Vitamin D is an essential fat-soluble vitamin that is primarily obtained from sun exposure, as well as dietary intake or supplementation. Deficiency in this vitamin can lead to diseases or disorders that negatively impact health, particularly in children, premenopausal women, the elderly, and athletes. There are two forms of vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol), and a concentration above 15 ng/ml is considered adequate for good health. This vitamin has many functions, including regulating calcium and bone health, immune function, muscle function, cardiovascular health, and hormonal balance, making it a nutrient of great interest.
References
- [1] Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. South Melbourne, VIC, Australia: Cengage Learning, 2012.
- [2] Holick MF. Vitamin D: Physiology, Molecular Biology, and Clinical Applications. Totowa, NJ: Springer Science & Business Media, 2013.
- [3] Chiang CM, Ismaeel A, Griffis RB, Weems S. Effects of Vitamin D Supplementation on Muscle Strength in Athletes: A Systematic Review. J Strength Cond Res. 2017;31(2):566-574.
- [4] Dusso AS, Brown AJ, Slatopolsky E. Vitamin D. Am J Physiol Renal Physiol. 2005;289(1):F8-28.
- [5] Grimaldi AS, Parker BA, Capizzi JA, Clarkson PM, Pescatello LS, White MC, Thompson PD. 25(OH) vitamin D is associated with greater muscle strength in healthy men and women. Med Sci Sports Exerc. 2013;45(1):157-62.
- [6] Hamilton B. Vitamin D and human skeletal muscle. Scand J Med Sci Sports. 2010;20(2):182-90