# Vitamin D in Switzerland: Supply Status and Supplementation

> Switzerland's geographical location affects the body's own vitamin D synthesis. What the research says about supply levels and what role supplementation can play.

Vitamin D is essential for numerous bodily functions, yet its endogenous production depends heavily on sun exposure. Particularly in regions at higher latitudes, the question arises of how to ensure an adequate supply. This also applies to Switzerland, where the sun's intensity is insufficient to meet the body's needs for much of the year.

## The latitude problem in Switzerland

The synthesis of vitamin D in the skin requires **UV-B radiation** in the 290-315 nm wavelength range. Switzerland lies at 46 to 47 degrees north, where the sun sits too low in the sky from **October to March**. During this period, UV-B radiation is filtered so heavily by the atmosphere that meaningful endogenous vitamin D production is physiologically impossible. Even extended time outdoors cannot compensate for the shortfall in these months. The Swiss Society for Nutrition (SGE) and the Federal Food Safety and Veterinary Office (BLV) therefore recommend **supplementation** during the winter half of the year.

## The vitamin D synthesis pathway

Vitamin D is activated in the body in several steps. First, UV-B radiation strikes **7-dehydrocholesterol** in the skin, producing previtamin D3. Body heat converts this into **vitamin D3 (cholecalciferol)**. In the liver, hydroxylation produces **25(OH)D3 (calcidiol)**, the storage form measurable in the blood. Calcidiol is then converted in the kidneys into **1,25(OH)₂D3 (calcitriol)**, the biologically active form. The 25(OH)D blood level serves as the benchmark for vitamin D status, with values below 50 nmol/l considered insufficient.

## Functions and synergies of vitamin D

The European Food Safety Authority (EFSA) confirms that vitamin D contributes to the normal function of the **immune system** as well as to the maintenance of normal **bones, teeth and muscle function**. These so-called health claims are based on extensive scientific studies. Vitamin D receptors (VDR) are found in almost all body tissues, underscoring the far-reaching importance of vitamin D beyond pure bone metabolism. For optimal effect, vitamin D often depends on cooperation with other nutrients.

Vitamin D promotes **calcium absorption** from the gut. **Vitamin K2 (MK-7)** directs the utilization of this calcium by activating osteocalcin, which guides calcium into the bones, and by activating matrix GLA protein (MGP), which keeps calcium away from the blood vessel walls. Combinations of D3 and K2 therefore make sense. **Magnesium** is an important cofactor for the enzymes that convert 25(OH)D into its active form. A magnesium deficiency can significantly impair vitamin D activation.

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## Frequently asked questions

**How much vitamin D should you supplement?**
The SGE recommends 600 IU daily for adults up to 60 years and 800 IU for people over 60. In preventive medicine, 1,000-2,000 IU daily are often targeted to reach a goal level of 75-125 nmol/l.

**Why is it important to take it with a meal?**
Vitamin D is fat-soluble. Taking it together with a meal containing dietary fat improves absorption considerably. On an empty stomach, bioavailability is significantly reduced.

**Can foods cover the vitamin D requirement?**
Fatty sea fish such as salmon or herring as well as eggs contain vitamin D, but in amounts that can hardly cover the daily requirement, especially in winter. Regular consumption in sufficient quantities is not practical for most people.

## Sources

SGE Reference Values 2020 - Vitamin D.
Holick MF (2007), New England Journal of Medicine - Vitamin D Deficiency.
Webb AR (2006), Journal of Steroid Biochemistry and Molecular Biology - Who, what, where and when.
EFSA Health Claims Vitamin D (2010).

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