Sun exposure and vitamin D production: for who, when, how much and how?

HUN Blog from 11/04/2020

Vitamin D, or rather the D hormone, is involved in many metabolic processes, including the optimal functioning of the immune system. With the current coronavirus epidemic, it may be fashionable to pay more attention to the health of the immune system. Based on my studies so far, I believe that sun-produced vitamin D is one of the most effective and simplest tools we can use to strengthen our immune system. But who-when-how much and how? It does matter when you want to go for vitamin D hunting.

Vitamin D and sunbathing

Although it doesn’t have the same media coverage like the current epidemic, there has long been an epidemic of vitamin D deficiency in the modern world. The spectrum of sunlight varies according to both time of day and season, with each season having its own biological role. I have written previously about the importance of sunrise and morning sun exposure. In Hungary, the hours around noon and especially the period from April to October will be of interest for vitamin D production.

Heliotherapy in an old hospital

Vitamin D can be produced by sunlight, taken in from food or supplements and stored for a certain period of time. You cannot overdose on vitamin D from sunlight, you simply break down the excess. The vitamin D synthesised in the skin stays in the blood longer than the vitamin D in the diet. In addition, sunlight also promotes many other metabolic processes that food or vitamin D supplementation alone does not, and we can trace our African evolutionary roots back to this, which is why I believe sun exposure is the primary source of vitamin D for humans.

Photosynthesis of vitamin D

Image source: Holick, 2011

The synthesis of vitamin D by sunlight is a multi-step process, requiring UV (ultraviolet) radiation of sunlight on the skin and a cholesterol derivative molecule (7-dehydrocholesterol). UV (10-400nm) light is a broader region of the electromagnetic spectrum, UV-B (280-315nm) is a narrower wavelength region. Sunlight also contains UV-C (10-280 nm), which does not reach the Earth’s surface, and UV-A (315-400 nm), which is important in other biosynthetic processes. UV-B rays from sunlight enable the conversion of the 7-dehydrocholesterol molecule circulating in the blood into vitamin D3 in several steps. The wavelength range required for vitamin D synthesis is between about 295-300nm.

UV light fluctuations

VIS: visible light, UVA-UVB, IR: infrared

How much UV light reaches a person who wants to sunbathe depends largely on the time of day, season and geographical location. Generally speaking, UV-A is present all year round in Hungary, but only appears 1-3 hours after sunrise (above an angle of incidence of about 10-15°) and fades out a few hours before sunset. If we look at the UV index unit of measurement, this occurs approximately when it changes from 0 to 1 in the morning and vice versa in the afternoon.

UV-B is typically expected between about 9 and 16 hours depending on the season (above about 30° incidence angle), this range is largest in summer, narrowing in spring and autumn. The maximum UV-B radiation is measured at midday, around noon, between sunrise and sunset.

In Hungary (about latitude 45-48 degrees), UV-B is available from about mid-March to mid-October, with the strongest effects in summer. Below about 35 degrees latitude (from about Los Angeles, Tokyo, Gibraltar south to the equator through about Buenos Aires, Cape Town, Sydney), there is more or less photosynthesis of vitamin D from UV-B all year round.

Why did I write so much “about”? ?

Really accurate numbers would be possible if we had a spectrometer in our hands and measured every day. Fortunately, this has been studied in many studies, going back decades, so we have quite reliable ’abouts’. There are also smartphone apps nowadays, such as dminder, which – after setting a few parameters – can roughly calculate when UV-B is present in a given location and how much vitamin D we have synthesised while sunbathing.

What does the efficiency of vitamin D production depend on?

How much UV-B radiation we can absorb from sunlight depends on a variety of factors, the most important being the angle of incidence of the sun’s rays and the amount of free skin surface area. The more perpendicular the sunlight is to the earth’s surface, the more of it reaches it and the skin.

  • Geographical location: It makes a difference whether we are at the equator or on the Kamchatka peninsula.
  • Season: There can be a big difference between summer and winter depending on the geographical location.
  • Time of day: UV-B only appears in the sunlight spectrum at certain hours of the day in a given place and not necessarily in all seasons.
  • Altitude: For every 1 km increase in altitude above sea level, UV radiation increases by about 5-6%. So you get slightly more in the mountains than at low altitudes.
  • Reflective surface: It also matters whether there is a water surface, snow or other good reflective surface nearby, so you get more sunlight.
  • Atmospheric components: Ozone layer, cloud thickness, air pollution can reduce UV penetration.
  • Clothing, exposed skin surface: It does matter if you sunbathe in beach gear or 5 layers of winter clothing… According to Professor Holick, a vitamin D expert, at least ¼ of your body should be exposed to the sun, so not just the face, but at least the arms or legs.
  • Sunscreen: Stronger sunscreens block 95-98% of UV-B rays, including vitamin D synthesis.
  • Indoors or outdoors: Window glass doesn’t let UVB through, so it’s not worth trying to hunt for vitamin D indoors with the window closed between the four walls
  • Skin pigmentation: Skin type is also important. In general, darker skinned people need more sunlight than lighter skinned people to produce the same amount of vitamin D (up to 5-10 times difference!). The so-called Fitzpatrick scale can give a good approximation. Most Hungarians fall into the 2, 3 category on a scale of 1 to 6.
  • Age: A 70-year-old person has about 25% less vitamin D synthesis capacity than a 20-year-old. Of course, this is only a statistical average and may vary from person to person.
  • Electrosmog, light pollution: Artificial lights at night, blue lights, excessive electrosmog unfortunately interfere here too. They dehydrate and interfere with cholesterol conversion (see more by Dr. Jack Kruse on this).
  • Duration of sun exposure: In summer, up to 10-15 minutes a day can be enough to produce enough vitamin D, but in spring and autumn much more is needed.
  • Other factors: Nutrition, hydration, health status, presence of metabolic diseases (each of these would be a longer topic..)

What happens if we ‘run out’ of UV-B sunlight in the autumn and don’t get it all winter?

Fortunately, vitamin D will not disappear from our bodies, it is not a coincidence it is a fat-soluble type of vitamin. We can store it in the liver, in fatty tissue. Ideally, if we’ve been well fueled up during the UV-B rich months, we can pull it out until next spring. The other important thing to know is that our food also contains vitamin D. The best sources are cod liver and its oil, seafood, offal, eggs, mushrooms.

How do northern peoples manage optimal vitamin D levels?

What’s their secret if they get little UV-B sunlight for most of the year and spend a lot of time in their huts or well-clothed? Here it is worth separating the modern urbanites (who are really hardly ever outdoors and on a western diet) and those living in traditional natural conditions. The former group is also more likely to have low vitamin D levels, while the latter have no or minimal health risks. This is largely due to their diet, which consists almost exclusively of fatty foods of animal origin, rich in vitamin D and the light-absorbing omega-3 fatty acid DHA. They are also genetically adapted to more efficient vitamin D production and lower vitamin D levels.

How much is too much sun exposure?

It is difficult to give general advice on this because it is very individual. 1 MED (minimum erythema dose) is the amount of sun exposure that causes mild redness within 24 hours of exposure. Half to a quarter of that may be enough, according to Holick, 2-3 times a week for optimal vitamin D levels. A few minutes is better than none, but it’s better to be outside for at least 10-15 minutes at a time every day during UV-B periods (too), with as much free skin as possible. Avoiding sunburn of course. If there was too much sun exposure that day, then move to shade or dress up, perhaps use sunscreen if you have to be outside for longer periods. If you don’t experience side effects and are comfortable outdoors, why not stay outside longer?

The evergreeen sunbathing

With gradual and regular sun exposure throughout the year (including sun exposure in the morning), we can adapt to the sun to a large extent. I can back this up with my own experience over many years. I used to burn red in half an hour in the summer sun, sometimes with a headache, and I had to put on sunscreen if I was outside for longer. With my lifestyle changes, I have managed to stay outside almost all day in summer without protection, sunburn and other side effects. So I’m sticking to sunbathing as an ancient immune booster and recommend it to others. For those who don’t believe me, do your research! Below are some references…

Mihaly Safran Hungarian books

Learn more about the biological effects of sunlight and artificial lights in my books!


Join the next fitness camp and optimize your Vitamin D level on the beach!


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