Vitamin D: How to create it naturally with the Maxi UVB panel? | Mitochondriak®

  Vitamin D is something your body can produce on its own, but it needs UVB radiation hitting the skin at the right angle. In May, the doors to vitamin D season finally open across Central Europe, when the spring sun is truly strong enough to trigger vitamin D production in your skin. However, the results depend on timing, exposed skin area, and your skin type.

Why can't you produce vitamin D in winter and early spring, even when the sun is shining?

Your skin can only produce vitamin D when it is exposed to UVB radiation with a wavelength of 290 to 315 nm. In winter and early spring, the sun sits too low in the sky and most UVB rays scatter in the atmosphere before they can reach your skin.

This phenomenon is known as vitamin D winter. According to an analysis by Khanna et al. (2022), which compiled data from across Europe, vitamin D winter at latitudes 48 to 49° N (roughly the latitude of Munich, Vienna, or Paris) lasts from October to March. During these months, UVB radiation reaching the skin is so weak that vitamin D production is virtually zero, even on sunny days. [R]

This means that even if the sun was shining in February and you were outdoors, your body did not produce a single microgram of vitamin D. The reason is not the intensity of light but the angle at which the sun's rays hit the Earth's surface.

What is the solar zenith angle and why does it determine vitamin D production?

The solar zenith angle (SZA) is the angle between the sun and the point directly above your head. The lower the sun sits on the horizon, the greater the SZA and the longer the path UVB rays must travel through the atmosphere. When the SZA exceeds roughly 50 to 55°, the atmosphere filters out virtually all UVB radiation and vitamin D cannot be produced in the skin.

Research by Neville et al. (2021) from University College Cork confirmed that UVB radiation makes up less than 5% of total UV radiation from the sun, yet this minor component is the only one that triggers the conversion of 7-dehydrocholesterol into previtamin D3 in the skin. When the SZA is too large, UVB simply cannot pass through the ozone layer. [R]

In practical terms, for Central Europe (latitudes 48 to 49° N) this means:

• November to February: SZA stays above 55° throughout the entire day, no vitamin D is produced
• March: SZA drops below 55° only for a brief period around solar noon, production is minimal
• April: SZA drops below 50° between 11:00 and 13:00, vitamin D season begins
• May: SZA stays below 40° from 10:00 to 15:00, enabling full vitamin D production

When in May is the sun finally strong enough?

In May at Central European latitudes, a 5 to 6-hour window opens during the day when UVB radiation is strong enough for vitamin D production. This window spans roughly from 10:00 to 15:00 or 16:00 local summer time on clear days.

According to a global study by Kift et al. (2024) from the University of Manchester, vitamin D synthesis at latitudes above 40° N is limited to certain months of the year. At latitudes 48 to 49° N, the vitamin D season lasts approximately from April to September, peaking in June and July. [R]

May is therefore the first month when you can reliably build your vitamin D stores from sunlight in Central Europe. After a long vitamin D winter, this is exactly when you should start going outside and exposing your skin, ideally from 10:00 onwards on clear days.

Be mindful of cloud cover, though. Thick clouds can reduce UVB intensity by 50 to 80%, meaning that on an overcast May day your body may not produce sufficient vitamin D even if the time and solar angle are right.

How many minutes in the sun do you need for your daily dose of vitamin D?

To produce an adequate daily dose of vitamin D in May at latitudes 48 to 49° N, most people need 15 to 30 minutes of direct sunlight on exposed skin between 10:00 and 14:00, provided it is a clear day and at least 35% of the body surface is uncovered (arms, forearms, face, neckline, and ideally legs).

This figure is based on a review by Wacker and Holick (2013) published in Dermato-Endocrinology, which showed that brief sun exposure covering the hands, face, and legs for 5 to 30 minutes twice a week (depending on skin phototype) can generate sufficient vitamin D. [R]

The exact time depends on several factors:

It is important not to exceed the minimal erythemal dose (MED), the exposure time after which the skin begins to redden. The goal is not sunburn but a suberythemal dose where the body produces vitamin D while simultaneously building melanin protection.

What blocks vitamin D production in the skin?

Vitamin D is produced directly in the skin through the action of UVB radiation, but several common factors can significantly reduce or completely block this production, even when you are outdoors in the sun at the right time.

Clothing and glass. Ordinary glass (car windows, office windows) blocks virtually 100% of UVB radiation. If you are sitting behind a window, you are not producing any vitamin D. Similarly, clothing, even a thin t-shirt, catches most UVB rays before they reach your skin.

Chemical sunscreens. Sunscreens with SPF 30 and higher have been shown to reduce vitamin D production in the skin by 95 to 99%. Instead of automatically applying SPF before every sun exposure, we recommend gradual skin adaptation and sensible timing. Chemical filters also penetrate into the bloodstream and may disrupt the hormonal system. You can learn more about this approach in our article on solar callus and protection from sunburn.

Air pollution. Smog and elevated ground-level ozone further reduce UVB intensity, especially in cities. City dwellers may have lower vitamin D production compared to people living in rural areas.

Age and melanin. As we age, the amount of 7-dehydrocholesterol in the skin decreases. This is the precursor to vitamin D. According to Holick (2007), a 70-year-old person has roughly one quarter of the precursor compared to a 20-year-old. People with darker skin (higher melanin content) need longer exposure for the same level of vitamin D production, because melanin absorbs UVB radiation.

How to build natural skin protection instead of using SPF?

Your skin has a built-in mechanism for gradual adaptation to UV radiation called the solar callus. It involves a thickening of the skin and increased melanin production, which makes your skin progressively more resistant to sunburn while it continues to produce vitamin D efficiently.

Instead of automatically reaching for a sunscreen with chemical filters, we recommend gradual adaptation:

1. Start in April and May with morning sunlight (before 10:00), when UV intensity is lower but still beneficial for your eyes and circadian rhythm.
2. Gradually extend your time in stronger midday sun, starting with 5 to 10 minutes and adding a few minutes each day.
3. Expose your skin progressively, beginning with forearms and face, then legs and torso.
4. Never try to get a tan in a single day. Sunburn is the exact opposite of what you want to achieve.
5. If prolonged exposure is unavoidable (a full day at the beach after months spent indoors), use physical protection: clothing, shade, a hat.

You can read more about gradual adaptation and building a solar callus in our article Solar callus: how to build your sun tolerance in May.

Your grandmother worked in the fields from spring to autumn and never got sunburned, because she built this solar callus every year. Today's average person spends 90% of their time indoors and heads off on holiday with pale, unadapted skin, leaving them defenceless against UV. The solution is not more SPF but a return to gradual, natural adaptation. Read also our article Why didn't your grandmother get sunburned and you did?

A practical skin adaptation plan for May

If you have spent the entire winter indoors and your skin is pale and unadapted, here is a concrete 14-day plan for safely building a solar callus in May:

Days 1 to 3: Go outside in the morning between 8:00 and 9:30. Expose your forearms and face. Spend 15 to 20 minutes outdoors. At this time, UVA is stronger than UVB, which helps your skin prepare for more intense radiation.

Days 4 to 7: Move closer to midday, between 10:00 and 11:00. Also expose your neckline and neck. Stay outside for 10 to 15 minutes. Monitor your skin; if you see no reddening, you are on the right track.

Days 8 to 14: Add midday sun, 11:00 to 13:00. Expose your legs as well (shorts). Extend your sun time to 15 to 25 minutes. Your skin should already have a visibly darker tone and a thicker texture, which is a sign that your solar callus is building.

After two weeks, you will be able to spend 30 minutes or more in the May sun without risk of burning, while your body efficiently produces vitamin D, melanin, and endorphins. If even mild reddening appears during the adaptation process, go back a step and shorten your exposure time.

Can you produce vitamin D without sunshine using a UVB panel?

Yes. Clinical studies confirm that UVB radiation from an artificial source triggers the same photochemical reaction in the skin as sunlight, provided it contains wavelengths in the 290 to 315 nm range. On overcast days or when you simply cannot get outside, a UVB panel can supplement what the sun cannot provide.

A pilot clinical study published in Scientific Reports (2025) confirmed that controlled UVB light exposure was able to increase serum vitamin D levels and alleviate deficiency. [R]

This is where light therapy at home comes in. Mitochondriak® devices include, alongside red and near infrared light, a UVB wavelength of 295 nm, enabling them to stimulate the skin to produce vitamin D, melanin, and other important molecules. A single infrared panel can replace the sun on days when it is not shining. Specifically, the Mitochondriak® Maxi UVB Upgraded, which is currently available for pre-order with a 20% discount, was designed precisely for this purpose.

Practical tips for using UVB light on Mitochondriak® devices:

• Always combine UVB with red and NIR light (never use UV on its own)
• Start with 30 seconds of UV and gradually work up to a maximum of 3 minutes per session
• Use at least 2 hours after sunrise and no later than 2 hours before sunset
• Allow a minimum 2-hour break between sessions
• Before your first session, test your photosensitivity according to the instructions on our FAQ page

You can find a detailed guide on how to use UV light with Mitochondriak® devices in our article Vitamin D: why a tablet isn't enough and how to produce it naturally.

Which foods contain vitamin D?

Diet is a supplementary source of vitamin D, but food alone only covers a fraction of your daily requirement. Nevertheless, it is helpful to know which foods can support your 25(OH)D levels in May:

• Oily sea fish (salmon, mackerel, sardines, herring): the richest dietary source; one serving of salmon contains approximately 600 to 1,000 IU of vitamin D3
• Cod liver oil: one tablespoon provides around 1,360 IU
• Egg yolks: one yolk contains roughly 40 IU; eggs from free-range hens may contain more
• Game meat and organ meats: liver contains measurable amounts of vitamin D, especially from pasture-raised animals
• Sun-dried mushrooms (shiitake, maitake): contain vitamin D2, provided they were dried in sunlight

It is important to view food as a supplement, not a replacement for UVB exposure. The daily recommended dose of vitamin D is, according to various experts, 1,000 to 4,000 IU, while a typical diet provides at most 200 to 400 IU per day. The remainder must come from sunlight or a quality UVB source.

Frequently asked questions about vitamin D and sunlight in May

Can I produce vitamin D while sitting behind a window in my office?

No. Ordinary window glass blocks virtually 100% of UVB radiation, which is essential for vitamin D production in the skin. UVA rays do pass through glass, but they do not trigger vitamin D synthesis. To produce vitamin D, you need to be outdoors with exposed skin in direct sunlight.

Is 10 minutes of sun in May enough to top up my vitamin D?

For people with fair skin (phototype I and II), yes, provided at least 35% of the body is exposed between 10:00 and 14:00. People with darker skin or those over 65 need 25 to 40 minutes. On cloudy days, the required time increases significantly.

Why should I not use SPF sunscreen before a short time outdoors?

Sunscreens with SPF 30 and above block 95 to 99% of UVB radiation, which practically halts vitamin D production. For short exposures (below your MED), gradual skin adaptation is the better approach. Use sunscreen only for prolonged exposure on unadapted skin, for example on holiday after months spent indoors.

From which month can you start producing vitamin D from sunlight in Central Europe?

Meaningful vitamin D production from sunlight begins in Central Europe (latitudes 48 to 49° N) in April (around solar noon) and the full season runs from May to September. From October to March, UVB radiation at these latitudes is too weak for vitamin D synthesis.

Is vitamin D from a supplement tablet as effective as from UVB light?

Not quite. Vitamin D from a tablet (D3) is absorbed through the digestive tract, while UVB exposure produces it directly in the skin together with other beneficial molecules (melanin, endorphins, nitric oxide). A tablet is a safety net for the winter months, but it does not replace the full spectrum of benefits that natural or high-quality artificial UVB light provides.

What should my blood vitamin D level be?

The optimal 25(OH)D blood level is, according to most experts in mitochondrial health, above 40 ng/ml (100 nmol/l). Standard laboratories consider 30 ng/ml to be normal, but from a prevention and performance perspective a higher level is more advantageous. After winter, you should have your levels checked with a blood test.

Can you overdose on vitamin D from the sun?

No, you cannot overdose on vitamin D from sunlight. Your body has a built-in regulatory mechanism. Once enough previtamin D3 is produced in the skin, further UVB radiation converts it into inactive metabolites. Overdosing is only possible through excessive use of supplements (tablets).

What should I do on overcast May days when the sun is not shining?

If the sun is not shining for several days in a row, you can supplement your vitamin D with a UVB panel at home. Mitochondriak® devices with a wavelength of 295 nm can trigger the same photochemical reaction in the skin as sunlight. Your second option is foods rich in vitamin D (oily fish, egg yolks) and vitamin D3 supplements.

Summary

May is the first full month for producing vitamin D from sunlight in Central Europe. The key to success is going outdoors between 10:00 and 15:00, exposing at least 35% of your body, and not coating your skin with chemical SPF for short exposures. Adapt your skin gradually, build your solar callus, and on cloudy days make use of devices with UVB light.

Curious about how to make the most of the spring vitamin D season? Check out our Mitochondriak® infrared panels with added UV.

Scientific studies and references

1. Khanna T. et al. Comprehensive Analysis of Seasonal and Geographical Variation in UVB Radiation Relevant for Vitamin D Production in Europe. Nutrients. 2022. PMC9735494
2. Neville JJ. et al. Physical Determinants of Vitamin D Photosynthesis: A Review. JBMR Plus. 2021. PMC7839826
3. Kift RC. et al. Globally Estimated UVB Exposure Times Required to Maintain Adequate Vitamin D Status. Photochemistry and Photobiology. 2024. PMC11124381
4. Wacker M., Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermato-Endocrinology. 2013. PMC3897598
5. Nature Scientific Reports. A pilot clinical trial to explore the effects of UV exposure on vitamin D status. 2025. doi:10.1038/s41598-025-09203-8
6. Kallioğlu MA. et al. UV index-based model for predicting synthesis of (pre-)vitamin D3. Scientific Reports. 2024. PMC10861575