Is it worth taking vitamin D supplements during the summer?


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A research group of Semmelweis University has recently found that 9 out of 10 Hungarians have vitamin D deficiency by the end of the winter season. [1] We might think that vitamin D deficiency can become less severe, and we can overcome it as summer approaches and we are more exposed to sunshine, however, most of the time this is not the case.

The synthesis of vitamin D is affected by many factors:

  • The ability of the skin to synthesize decreases with aging. As we grow older, our skin is able to produce less than half of the amount of vitamin D that we can produce when we are young.
  • The browner your skin is, the more time it needs to produce a given amount of vitamin D. The vitamin D synthesis of tanned white people might decrease by 50%.
  • Modern people spend little time in the open air – and if they do venture out into nature, they apply plenty of sunscreen, which is known for not allowing UVB to get into the skin. (Spectrum UVB of the sunrays trigger the production of vitamin D in the skin.)
  • Not only the number of hours of sunshine matters, but the solar incidence angle as well. So that’s why it is relevant when we sunbathe during the day. In Hungary during summer, the period between 10.30 am and 4 pm should be targeted for the production of vitamin D!
  • High level of fructose intake inhibits the synthesis of vitamin D and it increases the breakdown of the vitamin! The diet of western culture is characterised by high fructose intake – due to the huge amount of processed foods in which fructose can be found as sweetener in the form of corn syrup. Fructose increases the production of enzyme 24-hydroxylase (which is responsible for the breakdown of vitamin D3) and inhibits the production of enzyme 1α-hydroxylase (which contributes to the synthesis).

So in theory, sunbathing during summer would be an excellent way to reach the optimal level of vitamin D. However, it appears that in practice many factors can inhibit the synthesis of vitamin D.

Reaching the optimal level of vitamin D is essential for everyone, but it is of high importance for sportspeople since, as we can see, it affects not only our health condition, but sports performance as well.

In a study involving 35 people, researchers randomly divided the participants into two groups. The members of both groups had low level of vitamin D.

One of the groups received a daily dosage of 5,000 IU of vitamin D3 for four weeks, while the people in the other group received only placebo.

After four weeks, the level of strength and the level of serum vitamin D concentration of the members of the group receiving vitamin D increased significantly, while these levels of the group receiving placebo only remained the same. [2]

A blood test is the easiest way to find out whether you as a sportsperson need to take vitamin D during summer, and if so, what amount you need.

Vitamin D levels are considered deficient below 50 nmol/L, low between 50 and 75 nmol/L and normal between 75 and 150 nmol/L.

You can find two types of vitamin D in our range of products: Vitamin D3 and Vitamin D3 Forte. Both products – as their names suggest – contain vitamin D3 which is the form of vitamin D that can be best utilized by the body.


[1] 2nd Hungarian consensus on the role of vitamin D in the prevention and treatment of diseases.

[2] Jung, H. C., Seo, M. W., Lee, S., Jung, S. W., & Song, J. K. (2018). Correcting vitamin D deficiency improves some, but not all aspects of physical performance during winter training in Taekwondo athletes. International Journal of Sports Nutrition and Exercise Metabolism, 3. 1-25.