Sunlight and vitamin D: what I learned about summer in Moscow

With three months of summer ahead, I started wondering: do we really get vitamin D from sunlight in Moscow and central Russia, or are we just romanticising our walks?

It turned out to be less straightforward than I thought. 🧐

Vitamin D is not produced by “sunshine in general”.

Not by warmth.
Not by how bright the day is.
Not simply by the fact that it is summer outside.

Production is triggered by a specific part of the solar spectrum: UVB ultraviolet radiation.

The skin contains a substance with a slightly intimidating name: 7-dehydrocholesterol. When UVB reaches it, it turns into a precursor of vitamin D3, which the body then converts into its active form.

And this is where things get interesting.

The very same UVB that helps produce vitamin D can cause sunburn and damage DNA in skin cells.

There is no separate “good sun for vitamin D” and “bad sun that causes cancer”.

It is the same wavelength range.
The difference is the dose.

In summer, getting vitamin D from sunlight in Moscow and central Russia is possible. Especially in June, July and August, when the sun is higher, the days are longer, more skin is exposed and the necessary UVB reaches the surface.

But that does not mean “I need to start sunbathing right away”.

Quite the opposite.

A tan is not a sign of health.
It is the skin's protective response to damage.
And sunburn is a signal that there has been too much ultraviolet exposure.

Another point: lying in the sun does not make vitamin D rise indefinitely. Beyond a certain dose, the body does not keep producing more benefit. Skin damage, however, continues to accumulate.

So “I'll roast myself for vitamin D” is a bad strategy. 👎🏽

A better approach:
brief exposure to sunlight: yes;
sunburn: no;
aiming to get a tan: questionable;
aiming to spend a little time in daylight: fine.

How much is enough?
There is no universal number. It depends on skin phototype, time of day, cloud cover, the area of exposed skin, age, air pollution and the UV index.
You may come across guidelines such as 5-15 minutes with the hands, forearms or legs exposed. But without accounting for conditions and individual characteristics, I cannot justify that figure for Moscow or treat it as a safe standard.

Skin redness cannot be relied on as the sole measure of safety. No sunburn does not mean no damage.
If your skin is red, burning or painful by evening, you have overdone it.

Moscow has another particular factor: the air.

Moscow is not just a latitude; it is also a big city, with dust, aerosols, exhaust fumes and fine particles. All of these scatter and weaken solar radiation.

Air pollution can also affect UVB, the shortwave part of the spectrum. The size of the effect depends on the composition of the air and the conditions; I do not provide specific measurements for Moscow here.

So you can get a strange situation: the day is bright, warm and sunny, yet less of the “vitamin-producing” part of the spectrum reaches your skin than you might think.

Summer walks are wonderful. For mood, sleep, movement and feeling alive.
But “I walk in summer, so my vitamin D must be fine” is not necessarily true.

In the south, in Krasnodar, Sochi and Crimea, the situation is a little different.
The sun is higher, there is more UVB and the season is longer. It is easier to get vitamin D, but also easier to get sunburned. Especially near water, in windy conditions, in the mountains and around midday.
My takeaway for the south is this: conditions for vitamin D synthesis may be more favourable, but UV exposure still requires care. This does not yield a universal safe window measured in minutes.

In autumn, winter and early spring in Moscow, sunlight matters for mood and biological rhythms, but it is a weak source of vitamin D.

My conclusion for the summer:
the sun is not an enemy;
the sun is not a pill;
the sun is a powerful natural influence that needs to be handled sensibly.
Walking: yes.
Spending time in daylight: yes.
Occasionally letting your skin have brief exposure to the sun: yes.
Getting sunburned: no.
Deliberately tanning “for vitamin D” is a bad idea.

If deficiency is a concern, it is useful to discuss with a doctor whether a 25(OH)D test is indicated. The Endocrine Society guidelines do not recommend testing every healthy adult routinely.

That is the main point of the article. What follows is for curious minds. 🙂‍↔️

Skin cancers are caused primarily by ultraviolet radiation, rather than visible light or heat.

UVC: 100-280 nm.
Very dangerous, but almost entirely blocked by the ozone layer.

UVB: 280-315 nm.
The main cause of sunburn; it directly damages DNA and is linked to skin cancer.

UVA: 315-400 nm.
Penetrates more deeply, causes oxidative stress and skin ageing, and also increases cancer risk.

Think of it this way: the range of ultraviolet wavelengths harmful to skin is broad, while the “useful window” for vitamin D is small, variable and dependent on a host of conditions.

Vitamin D can come from food and supplements when they are needed. Do not order tests or start taking tablets based only on this note: the need depends on your circumstances. Take care of yourself, and stay energetic and happy!