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Dossier: Strong bones and muscles also depend on vitamin D**

Bone density is often mentioned in the same breath as calcium. Thanks to years of work to inform the public, many people now appreciate the importance of another nutrient for strong bones: Vitamin D. A dossier published last year in Deutsche Medizinische Wochenschrift (German Medical Weekly) updated basic specialist knowledge of vitamin D and bone density. We have compiled a few interesting excerpts below to help you refresh your knowledge of vitamin D.**

  • Vitamin D basic knowledge

Although vitamin D is considered a vitamin, it does not actually fit the definition. It has the characteristics of a hormone and only a small proportion of it comes from our food. Instead, the body’s main source of vitamin D is endogenous synthesis of the vitamin in skin tissue due to exposure to sunlight.

  • Vitamin D status

To be able to absorb calcium from the gut and incorporate it in our bones, our bodies need an adequate supply of vitamin D. In most cases, this supply is assessed based on the level of the biologically active form of the vitamin, also known as 25-OH vitamin D. The optimal level has not yet been conclusively determined, but the most commonly used measure is the classification established by Prof. Michael F. Holick and his colleagues.**

Vitamin D serum levels


<25 nmol/l (<10 ng/ml)

Severe vitamin D deficiency

<50 nmol/l (<20 ng/ml)

Vitamin D deficiency

51–72 nmol/l (21–29 ng/ml)

Vitamin D level insufficient


Ideally, a vitamin D deficiency should be avoided altogether. As an insufficient supply of vitamin D can remain asymptomatic for long periods, blood analysis can bring clarity. Almost everyone would be well advised to arrange laboratory diagnostic testing of their vitamin D levels because, according to internationally published studies, large parts of the population do not have an adequate supply. Regular checks of vitamin D levels are essential, particularly for certain high-risk groups (e.g. people with dark skin, the elderly and expectant mothers).**

  • On vitamin D and bone density

A winter-related fall in a person’s vitamin D level is associated with a rise in their parathormone level. This hormone is among the substances to play a key role in calcium-phosphate metabolism. An elevated parathormone level increases calcium absorption in the gut and releases calcium from the bones. Post-menopausal women in particular may experience a significant reduction in bone density if their calcium intake is too low. In this case, micronutrient interventions containing calcium and vitamin D would certainly be recommended.

  • On vitamin D and muscle function

We now know that vitamin D, which our body creates when exposed to direct sunlight, is vital – not only for strong bones but also for normal muscle function. For example, a meta-analysis of 310 young and healthy subjects has shown that vitamin D supplements increase muscular strength in the upper and lower extremities. Another meta-analysis of 5615 older subjects confirmed the positive effect of vitamin D on muscular strength, with particularly pronounced results in cases where subjects previously had an insufficient supply of vitamin D. Given that muscle mass and muscle function decline over the age of 50 in particular, a good vitamin D supply is certainly important and desirable for older people.

Researchers’ key statements at a glance**

  1. A good supply of vitamin D is important for maintaining healthy bone density and supporting muscle function.
  2. Large parts of the population – especially high-risk groups – should have their vitamin D level tested.
  3. Vitamin D supplements (of 800–1000 IU per day) support muscle function.
  4. As vitamin D2 raises the vitamin D level to a lesser extent, healthy people should opt for vitamin D3.


Conclusion: As well as being important for maintaining healthy bone density over the long term, a good supply of vitamin D also supports normal muscle function. The researchers state that if a person is identified as having a vitamin D deficiency, it must be rectified. They recommend vitamin D supplements in the form of vitamin D3.**


Literature: Schlereth, F. et al. 2019. Osteoporose – gibt es Indikationen für eine Vitamin-D-Therapie? Dtsch Med Wochenschr. 144: 1120–40.

**These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

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