As is often the case, the research data is contradictory, but we still managed to find out some useful facts.
Vitamin D plays an important role in the body, regulating many metabolic processes. Its lack may lead to osteoporosis (decreased bone density) and rickets. There are recommendations for vitamin D supplementing that are applicable to ordinary people.
What about those who expose themselves to heavy and prolonged physical exercising? Can vitamin D be helpful to increase their bone strength, boost immunity and help build muscle tissue?
That is what we managed to find out.
Prehistory: how vitamin D was discovered and why it has such a name
Vitamin D was discovered in the 1920s by the pioneer of sports nutritional medicine Elmer McCollum. This American scientist previously discovered vitamin A in fish oil.
It has been found that dogs fed with fish oil do not suffer from rickets. McCollum suggested that vitamin A or another substance in fish oil helps to fight rickets. Neutralizing vitamin A in fish oil, he started giving it to dogs with rickets, and they got better.
The previously unknown substance got the name vitamin D, since it was the fourth vitamin discovered by scientists. A little later, in 1923, it was proved that food irradiated with ultraviolet light contains increased content of this vitamin. In addition, the assumption that a person is able to produce it in case of sunlight exposure received the proof.
Where does vitamin D come from and why we need it?
Vitamin D is a collective term that includes vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). D3 is produced under the action of ultraviolet rays in the skin. Also, it comes with some foods. Vitamin D2 can only be ingested into the human body with foods.
Here are vitamin D functions that are directly related to sports: improving muscle performance and recovery, maintaining bone health and immunity.
Vitamin D deficiency carries the risk of stress fractures, anemia, and weakened immune system. Together, this seriously reduces the athletic performance.
The main sources of vitamin D are sunlight (70–80%) and food (20–30%).
With insufficient number of sunny days per year or eating disorders, a person may develop a deficiency of this vitamin.
Vitamin D can be found in fish oil, eggs, cod liver, chum, mackerel, pink salmon, goat milk and other foods.
Recommendations for ordinary persons and athletes
Unfortunately, the mechanism of vitamin D deficiency formation is not completely clear. Because of this, there are diverse and often conflicting recommendations on how to monitor the level of this vitamin in the body and how to take it.
Thus, when assessing the level of 25[OH]D (a biologically inactive substance that allows to evaluate the vitamin D reserves in the body), athletes often show significant performance fluctuations.
There can be various reasons for this: number of sunny days per year, type of training clothes, dietary habits, training cycle phases.
For example, a study conducted with NFL players showed reduced levels of vitamin D in their blood, resulting in more muscle injuries than in athletes with normal levels of this vitamin.
This observation was confirmed by a large review, published in 2015 in Sports Medicine journal. The authors showed that 56% of athletes had vitamin D deficiency. At the same time, the results of a survey conducted by the National Academy of Medicine of the USA showed that the average level of vitamin D in the population is within the normal range.
There is a confusion with guidelines for maintaining normal vitamin D levels in athletes. Various schemes exist. They range from simple administration of 1000 IU per day to a complete weekly dose of 100,000 IU. At the same time, recommendations for ordinary people are more specific - 600 IU per day, with an increase in dose to 800 IU per day after the age of 70.
What are the norms of vitamin D content in the body?
One of the reasons for the confusion about vitamin D level in blood is associated with the definition of “normal” values of this substance.
The most common test used to determine the level of vitamin D in blood measures the concentration of 25[OH]D (calciferol, 25-hydroxyvitamin D). It is a biologically inactive substance, a precursor of a biologically active vitamin D, which does not always correctly reflect how much vitamin D is in the body in the form of active substance.
The accepted standard levels of vitamin D in the blood also vary: they are lower in the recommendations of the National Academy of Medicine (40–80 ng/ml) and higher in the recommendations of the Society for Endocrinology (30–100 ng/ml).
In addition, there are factors that reduce the level of vitamin D in the body. For example, if you live in the north, where the number of sunny days is small, or you work long hours in the office and move around the city in transport.
Some people consciously avoid direct sunlight for fear of developing skin cancer. Although this is a good reason, you need to understand that contact with ultraviolet for 10-15 minutes a day will help you get a daily dose of vitamin D.
People with delicate skin sensitive to the sun should use sunscreens that block part of the UV. People with dark skin are better protected from the negative effects of UV, but because of this, the possibilities for the synthesis of vitamin D are limited.
How vitamin D affects performance
Despite the large number of studies on the vitamin D effect on performance, there is still no definitive answer to this question.
Those studies in which the intake of vitamin D led to increased efficiency and effectiveness, for example, in football players or rowers, have several limitations. A small number of athletes participated in the studies, and it is not very clear how a performance increase was obtained.
Did athletes have an initial vitamin D deficiency and high doses (5,000–6,000 IU/week) normalized its blood levels and led to improved performance? Alternatively, did these athletes have normal vitamin D levels and additional supplementing helped them improve performance?
All this leads to the conclusion that improved performance under the influence of increased vitamin D intake has not yet been definitively proven.
Also To Read: 9 Best Supplements for Runners
To sum up: is it necessary to supplement vitamin D?
Since vitamin D is produced under the influence of UV rays, spending more time outdoors on a sunny day helps to maintain its reserves.
Do not forget that about 20-30% of vitamin D comes to us with food (fish oil, eggs, cod liver, chum, mackerel, pink salmon, and goat milk), so a varied and nutritious diet also helps maintain its normal level in the body.
Residents of regions with not enough sunlight, especially in winter, should maintain their vitamin D levels by taking 600–800 IU per day (preferably in the form of vitamin D3).
For sports enthusiasts, the recommended daily intake is slightly higher, from 1000 to 2000 IU daily. Despite the fact that the effect of vitamin D on athletic performance is not fully understood, its deficiency in athletes is quite common, especially in winter, therefore, it is recommended to supplement it.
However, you need to understand that excessive vitamin D intake (4000 IU per day or more) is harmful, and can lead to hypercalcemia. This is an elevated level of calcium in the blood, manifested by nausea, vomiting, and frequent urination.
To find out, if you need vitamin D, you need to pass a blood test. This is a simple and affordable method to analyze your current vitamin level in the blood and help you understand whether to supplement it or not.
It makes sense to take this vitamin in the dark season - in fall and winter, when the number of sunny days is reduced. In addition, your diet should be varied, and include foods high in vitamin D.
Together, this will help you successfully fight infections, reduce the risk of stress fractures and improve your athletic performance.
Sources:
- Monaghan C, McIlvenna LC, Liddle L, Burleigh M, Weller RB, Fernandez BO, Feelisch M, Muggeridge DJ, Easton C. The effects of two different doses of ultraviolet-A light exposure on nitric oxide metabolites and cardiorespiratory outcomes. Eur J Appl Physiol. 2018 May;118(5): 1043–1052.
- Owens DJ, Allison R, Close GL. Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports Medicine (Auckland, N.z). 2018;48(Suppl 1): 3–16. doi:10.1007/s40279-017-0841-9.
- Baker JS, McCormick MC, Robergs RA. Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise. Journal of Nutrition and Metabolism. 2010;2010:905612.
- Dahlquist DT, Dieter BP, Koehle MS. Plausible ergogenic effects of vitamin D on athletic performance and recovery. J Int Soc Sports Nutr. 2015 Aug 19;12:33.
- Abrams GD, Feldman D, Safran MR. Effects of Vitamin D on Skeletal Muscle and Athletic Performance. J Am Acad Orthop Surg. 2018 Apr 15;26(8): 278–285.
- Larson-Meyer E. Vitamin D supplementation in athletes. Nestle Nutr Inst Workshop Ser. 2013;75:109–21.
- Ogan D, Pritchett K. Vitamin D and the athlete: risks, recommendations, and benefits. Nutrients. 2013 May 28;5(6): 1856–68.
