In 1919, British physician Harriette Chick conducted groundbreaking studies on rickets in Vienna, demonstrating that light and nutrition play central roles in achieving strong bones. Her work marked a turning point: sunlight is medicine – but in the right dose. Today, high performers face a similar balancing act: protecting skin from UV damage while ensuring adequate vitamin D levels. Both are possible when we cleverly combine science and everyday life.

Vitamin D is a hormone-like vitamin that the body synthesizes through the skin with the help of UVB radiationa component of sunlight with wavelengths of ~290–320 nm that initiates the body's vitamin D synthesis. In the blood, we measure 25(OH)D25-hydroxyvitamin D, the stable storage form of vitamin D as a status marker. Sunscreen remains essential because UV radiationultraviolet radiation that can lead to skin aging and increase the risk of skin cancer damages DNA. Therefore, the key is dynamic management: situationally adapted UV protection combined with nutrition, fortification, and supplements. D3 (cholecalciferol) is the most common form in foods and supplements; D2 (ergocalciferol) is also used. The goal is to achieve a 25(OH)D range that supports muscular function, bone health, and performance – without endangering the skin.

An adequate vitamin D status supports bone metabolism and muscle strength; severe deficiencies increase the risk of rickets, osteomalacia, and likely falls and fractures – there is consensus and a duty of care on this matter ^[1]. At the same time, uncontrolled UV exposure is a clear risk factor for skin cancer. Indoor tanning in solariums offers no health benefits but significantly increases skin cancer risk and can shift the UVA/UVB balance to make it more harmful for the skin than summer sunlight ^[2]. For everyday life, this means: yes to vitamin D – but not at the cost of DNA damage. Safer sources through diet, fortified products, and well-dosed supplements are better to ensure consistent skin protection ^{[3] [1]}.

Randomized studies show that fortified milk and yogurt reliably raise 25(OH)D levels. A recent evaluation of 35 RCTs involving 4,965 participants found significant increases with D3-fortified milk and yogurt as well as with D2-fortified milk; even cheese showed a potential benefit after sensitivity analysis. Key takeaway: fortification is a practical lever, especially in months with little sunlight or with consistent UV protection ^[3]. An international position paper contextualizes: vitamin D is central to the musculoskeletal system; supplements should aim to avoid deficiencies at a population level, not blindly maximize levels. It emphasizes the role of season, skin pigment, clothing, and supplement use, recommending targeted strategies over blanket measurement or high-dose protocols ^[1]. For managing UV exposure, technologies are coming into focus: reviews show that smartphone apps and connected sensors can predict or measure the UV index to plan individual safe exposure times – a pragmatic way to protect the skin while still utilizing short, safe light windows ^[4].

- Plan your vitamin D intake through your plate: include fatty fish (e.g., salmon, mackerel), eggs, and fortified milk or plant-based alternatives 2–3 times a week. Fortified milk/yogurt significantly increases the 25(OH)D level – particularly helpful in sun-deficient periods ^[3].
- Supplement strategically in autumn/winter or with low sun exposure: choose vitamin D preparations after consulting with a physician and tailor to personal factors (skin type, lifestyle, region). Aim to avoid deficiencies, not maximize ^[1].
- Avoid solariums as a "vitamin D source": they increase skin cancer risk and provide an unfavorable UVA/UVB profile – health benefits are not proven ^{[2] [5]}.
- Manage UV exposure wisely: use UV index apps or wearables to coordinate time of day and duration of stay. This allows for short, low-risk outdoor outings without risking overexposure ^[4].
- Avoid high-dose experiments: no indiscriminate, permanent high consumption of vitamin D to "replace" sunlight. Incorrect dosages can lead to hypercalcemia – preparations vary in units and concentrations ^[6].

You do not have to choose between skin protection and vitamin D: with fortified foods, smart supplements, and UV index management, both can be achieved. Next step: install a UV app, expand your shopping list with fortified products and fatty fish, and set an appropriate winter dose with your doctor.