Vitamin D – importance and dosage in strength training

Vitamin D is a fat-soluble vitamin, but its importance in the body goes beyond simply taking one capsule a day. It is a component that the body can produce in the skin under the influence of UVB radiation, and at the same time it can be supplied through diet and supplements. In food, it occurs naturally primarily in fatty fish, cod liver oil, egg yolks and, in smaller amounts, in other animal products; some products available on the market are also enriched with vitamin D. For this reason, it is best to think of it first as an element of daily physiology and food, and only then as an ingredient in supplements.

1. This is no coincidence
2. Why is vitamin D important for strength training?
3. What else is worth knowing about vitamin D?
4. D3 or D2?
5. Dosage in practice
6. Vitamin D in the diet of a person who exercises
7. Summary

This is no coincidence

In strength training, the topic of vitamin D comes up very often, but it is worth discussing it in detail. Not because it is a "vitamin for athletes", but because authorised claims for vitamin D include areas such as maintaining normal muscle function, maintaining healthy bones, normal absorption and utilisation of calcium and phosphorus, and maintaining normal blood calcium levels. It is these functions that make strength trainers pay special attention to vitamin D.

Why is vitamin D important for strength training?

Muscles, bones and the musculoskeletal system

Strength training is based on the work of muscles and the musculoskeletal system, which is why vitamin D naturally fits into this context. From the perspective of authorised statements, the most important thing is that vitamin D contributes to the maintenance of normal muscle function and helps maintain healthy bones. This is enough to consider it an essential component in the diet of a physically active person, without the need to add excessive, unauthorised properties.

In practical training terms, this simply means that vitamin D is part of the basic nutritional support system, rather than a supplement with "special sporting effects". People who do strength training tend to be more conscious of the nutrients that are important for muscles, bones and everyday bodily functions, which is why vitamin D is so often included in supplementation plans. There is no need to build up a sensational narrative here. Its role is important enough at the level of ordinary physiology.

Calcium and phosphorus are also important

Vitamin D also contributes to the normal absorption and utilisation of calcium and phosphorus and to the maintenance of normal blood calcium levels. This is why it so often appears alongside calcium or vitamin K in foods and supplements. In the context of strength training, it is not about a spectacular "boost", but about its participation in the basic processes related to the body's mineral metabolism. This is a calmer but much more reliable way of talking about vitamin D.

What else is worth knowing about vitamin D?

Vitamin D is a compound whose supply depends on several sources simultaneously: exposure to sunlight, diet, fortified foods (if any) and supplements. For this reason, not everyone functions under the same conditions. The season, time spent outdoors, diet, age, body weight and overall lifestyle are all important factors. The 2023 Polish recommendations emphasise this diversity and indicate that daily vitamin D intake should depend on age, body weight, time spent in the sun, eating habits and lifestyle.

It is also worth remembering that vitamin D is a fat-soluble vitamin. From a practical point of view, this means that vitamin D supplements are usually recommended to be taken with a meal containing fat. It is a simple detail, but it is often such details that determine whether the use of a supplement is orderly and logical, or whether it boils down to just mechanically swallowing a capsule.

D3 or D2?

There are two main forms commonly found on the market: vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol. Polish recommendations indicate cholecalciferol as the first choice for supplementation. This is why the D3 form dominates in most preparations available on the market. From the user's point of view, it is therefore more important than the marketing name itself to check whether the product contains D3, what the dose per serving is and whether the description is clear.

Dosage in practice

For adults aged 19-65, current Polish recommendations usually indicate 1000-2000 IU per day. From May to September, adequate exposure to the sun may be sufficient, but additional supplementation in this regard is considered recommended and safe. For people aged 65–75, 1000–2000 IU per day is also recommended throughout the year, and for people over 75, 2000–4000 IU per day is recommended throughout the year.

In strength training practice, it is not worth assuming that the mere fact of exercising automatically means that very high doses are needed. It is much more reasonable to think of vitamin D as a component whose supply should be adjusted to age, season, sun exposure, diet and the actual status of the body. This is why testing 25(OH)D levels is often considered the most systematic way to individualise supplementation, especially when someone wants to select a dose more precisely than just "by eye".

At the same time, it is necessary to distinguish between nutritional recommendations and the rules for labelling supplements in Poland. The Dietary Supplements Team at the Chief Sanitary Inspectorate (GIS) indicates the maximum level of vitamin D in dietary supplements as 2000 IU for a healthy adult population up to 75 years of age and 4000 IU for healthy individuals over 75 years of age, with the labelling clearly indicating the target group. This is an important detail from the perspective of the market and legal communication about products.

Vitamin D in the diet of a person who exercises

People who do strength training usually focus on protein, creatine, energy and recovery, but vitamin D is an example of a component that should be treated more fundamentally. Not as a "trendy supplement", but as part of everyday nutrition and physiology. Oily fish, eggs and fortified products can be part of this puzzle, with supplements becoming a complement rather than the only source of support. This way of thinking is usually the most stable and best suited to a long-term approach to diet.

Summary

Vitamin D makes sense in the context of strength training, not because it promises "athletic results", but because it participates in basic functions that are important for active people: it contributes to the maintenance of normal muscle function, helps maintain healthy bones, supports the normal absorption and utilisation of calcium and phosphorus, and maintains normal blood calcium levels. This is entirely sufficient to take it seriously in the diet of a person who trains.

When it comes to dosage, it is safest to rely on current recommendations and real-life conditions, rather than the belief that "the more, the better". Polish recommendations for adults most often range from 1,000 to 2,000 IU per day, taking into account sun exposure, age and lifestyle, and if you want a more accurate adjustment, 25(OH)D testing is helpful. This version is practical, factual and consistent with a cautious approach to communication about supplements.

Sources:

• Vitamin D and Sport Performance https://pubmed.ncbi.nlm.nih.gov/32245151/
• Vitamin D and the athlete-patient: state of the art https://pubmed.ncbi.nlm.nih.gov/33833045/
• Effects of vitamin D supplementation on maximal strength and power in athletes: a systematic review and meta-analysis of randomized controlled trials https://pubmed.ncbi.nlm.nih.gov/37841405/