Why vitamin D is so important
Vitamin D belongs to the fat-soluble vitamins and occupies a special position in metabolism: with sufficient sunlight, the body can produce it itself in the skin. Only a small proportion of requirements is covered through food. Studies suggest that around 80 to 90 per cent of the vitamin D needed is formed in the skin through UVB radiation.
Strictly speaking, vitamin D is not a classic vitamin but a precursor to a hormone. In its activated form, it acts on numerous cells in the body – from bone and muscle cells to cells of the immune system.
Vitamin D deficiency: a widespread problem in Austria
A vitamin D deficiency is more common in our latitudes than many people assume. Various surveys show that a considerable proportion of the Austrian population – especially between October and March – is not adequately supplied with vitamin D. The reason lies in the geographical location: north of the 42nd parallel, UVB radiation in the winter months is barely sufficient to enable noteworthy endogenous production in the skin.
The following groups are particularly at risk:
- Older people, whose skin can produce less vitamin D
- People who spend most of their time indoors
- People with darker skin, as more melanin reduces UVB absorption
- Pregnant and breastfeeding women with increased requirements
- People with chronic gastrointestinal conditions or on certain medications
- Infants and young children
Even in summer, levels can be low – for example, if sunscreen is used consistently or little time is spent outdoors. Both, however, are basically sensible from a skin-protection perspective.
Importance for the bones
The best-known function of vitamin D concerns bone metabolism. It promotes the absorption of calcium and phosphate from the intestine and is therefore significantly involved in the mineralisation of bones.
- In children, a pronounced deficiency can lead to rickets.
- In adults, insufficient supply can be associated with softening of the bones (osteomalacia).
- In older age, a long-term deficiency can increase the risk of osteoporosis and bone fractures.
Adequate vitamin D supply is therefore an important pillar of bone health – alongside a calcium-rich diet and regular exercise.
Vitamin D and the muscles
Vitamin D also acts on muscle cells. Adequate supply can contribute to maintaining muscle strength and coordination. In older people, a connection between low vitamin D levels and an increased risk of falls is being discussed.
Vitamin D and sport
The topic of vitamin D and sport has been raised frequently in recent years. Physically active people are increasingly interested in whether good supply can support performance. Current data suggest that:
- a balanced vitamin D level contributes to normal muscle function,
- a deficiency is associated with reduced strength development and longer recovery times,
- athletes who mainly train indoors may have a higher risk of inadequate supply.
Supplementation alone does not increase athletic performance – it can, however, be useful in the case of a documented deficiency in order to cover requirements.
Vitamin D and the immune system
Vitamin D receptors are also found on many cells of the immune system. Vitamin D is involved in regulating defence reactions and can influence both the innate and the adaptive immune response. A balanced level can help maintain the normal function of the immune system. Indications of a possible connection with respiratory infections are currently being investigated further; sweeping promises are not appropriate here.
Measuring vitamin D levels: when does it make sense?
Anyone who wants to know about their own supply can have their vitamin D level measured. The so-called 25-hydroxy vitamin D value (25-OH-D) is usually determined in the blood. This value reflects the supply over the past few weeks.
A medically guided assessment can be particularly useful in the case of:
- persistent tiredness, muscle weakness or bone pain
- known risk factors (e.g. osteoporosis, chronic illnesses)
- after prolonged periods without sun exposure
- before starting higher-dose supplementation
- in highly active athletes with symptoms
Important: A blanket, non-medically supervised high-dose intake is not recommended, as vitamin D, being a fat-soluble vitamin, is stored in the body and can have undesirable effects in very high doses.
How can supply be improved?
The following measures can help prevent a deficiency:
- Make use of sunlight: in the summer months, 15 to 25 minutes a day with uncovered arms and face are often enough – without risking sunburn.
- Pay attention to diet: oily sea fish (e.g. salmon, herring, mackerel), eggs, certain mushrooms and fortified foods contain vitamin D, but usually only cover part of the requirement.
- Outdoor exercise: regular walks, including in winter.
- Supplementation after medical consultation: dosage and duration should be determined individually, ideally on the basis of a measured value.
The Austrian Nutrition Society recommends a daily intake of 20 micrograms (800 IU) for adults in the absence of endogenous synthesis. The individually appropriate dose can, however, differ from this and should be agreed with a doctor.
Conclusion
Vitamin D is an important building block for bones, muscles and the immune system. Particularly in Austria, supply is often borderline in the winter months. A medically guided assessment of the vitamin D level provides clarity and allows an individually tailored recommendation – whether in everyday life, with chronic complaints or in a sporting context. Blanket self-treatment is not advisable; a targeted, well-founded approach, on the other hand, can contribute to maintaining health.
This article does not replace medical advice.