Did you know that your body can produce a vitamin that affects immunity, mood, bones, muscles, and even heart and brain health? This is vitamin D , not without reason called the sunshine vitamin of life . Its synthesis begins in the skin when exposed to sunlight – this is one of the few cases where the body can "produce" the vitamin on its own. Unfortunately, living conditions in our latitude and modern lifestyle mean that many people struggle with vitamin D deficiency, often without even realizing it.
In this article we will take a closer look at:
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how exactly does natural vitamin D synthesis work in the skin,
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what factors influence its effectiveness,
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how much "sunshine time" we need each day,
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and when natural synthesis is no longer sufficient and it is worth considering supplementation.
You will also find recommendations for natural vitamin D supplements that will successfully supplement your vitamin D levels during months when there is little sunshine.
Make a cup of tea , sit comfortably and immerse yourself in reading – your health will thank you for it!
1. What is vitamin D?
Vitamin D is one of the most important biologically active substances in the human body, although, despite its name , it's not a classic vitamin . In fact, it acts like a hormone, influencing hundreds of metabolic and regulatory processes. That's why maintaining its proper levels is so crucial for physical and mental health.
1.1. Types of Vitamin D: D2 and D3
Vitamin D comes in two main forms:
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Vitamin D2 (ergocalciferol) – of plant and fungal origin, found e.g. in yeast or mushrooms exposed to UV rays.
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Vitamin D3 (cholecalciferol) – produced by the human body in the skin under the influence of UVB radiation, also found in animal products (e.g. fatty fish, eggs, cod liver oil).
From an efficiency point of view:
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D3 is a more biologically active and better absorbed form than D2.
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That is why vitamin D3 is most often used in dietary supplements.
1.2. How does vitamin D work in the body?
Once absorbed from food or produced in the skin, vitamin D must undergo two stages of activation —first in the liver and then in the kidneys. Only then can it perform its biological functions.
The most important of them include:
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✅ Regulation of calcium and phosphate metabolism – crucial for healthy bones and teeth, prevents osteoporosis and rickets.
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✅ Supporting the immune system – vitamin D influences the production of antibodies and the activation of immune cells.
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✅ Contributes to muscle function – its deficiency may lead to weakening of muscle strength, especially in older people.
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✅ Impact on mood and nervous system – low levels of vitamin D are associated with depression, especially seasonal depression (SAD).
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✅ Potential role in preventing chronic diseases – research indicates a possible link with a lower risk of heart disease, type 2 diabetes and some cancers.
In short: vitamin D is the foundation of overall health , and its deficiency can have wide-ranging and often underestimated consequences.
1.3. Symptoms and effects of vitamin D deficiency
Vitamin D deficiency is a silent yet common health problem. It often develops without obvious symptoms , and its consequences can be long-term and serious. For this reason, vitamin D is sometimes called the "hormone of the 21st century"—its impact on health extends far beyond the skeletal system.
The most common symptoms of deficiency
In the early stages, deficiency can be difficult to diagnose because the symptoms are nonspecific. The most common include:
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chronic fatigue and weakness – lack of energy despite rest,
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low mood, depression, irritability – vitamin D affects the functioning of the nervous system and serotonin levels,
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reduced immunity – more frequent infections, colds, flu,
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muscle and bone pain , as well as a general feeling of being “broken”,
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problems with sleep and concentration ,
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in children – late teething, delayed motor development .
In adults, deficiency is often associated with non-specific symptoms that can be confused with other conditions – which only increases the risk of it being missed.
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More serious effects of long-term deficiency
Lack of adequate levels of vitamin D over a long period of time can lead to a number of disorders and diseases:
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🦴 Weakening of bones and muscles – greater risk of fractures, back pain, osteoporosis in the elderly, rickets in children.
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🧠 Mood and cognitive disorders – there is growing evidence linking vitamin D deficiency to depression, anxiety, memory impairment, and even Alzheimer’s disease.
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❤️ Increased risk of heart disease – including hypertension, atherosclerosis, heart attack.
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🦠 Weakened antiviral and antibacterial immunity – greater susceptibility to respiratory infections, flu, and even more severe COVID-19.
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🍬 Metabolic disorders – insulin resistance, increased risk of type 2 diabetes.
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🧬 Greater risk of developing certain cancers – including breast, prostate, and colon cancer (although research is still ongoing).
Why is it worth acting early?
Symptoms of vitamin D deficiency can be easily overlooked, often attributed to stress, fatigue, weather, or age. However, regular blood 25(OH)D testing and informed supplementation can prevent many health complications. The sooner we respond, the easier it is to restore balance and improve quality of life—without having to treat the serious consequences of deficiency.
2. Vitamin D synthesis in the skin
One of the most fascinating aspects of vitamin D is the fact that the human body can "produce" it on its own – and quite effectively, provided we provide it with the right conditions.
Solar radiation , specifically UVB radiation , plays a key role in this process. It initiates a chemical reaction in our skin that leads to the production of biologically active vitamin D3.
2.1. How does natural vitamin D synthesis work?
The process of vitamin D synthesis in the skin begins with the presence of 7-dehydrocholesterol , a natural fatty compound found in the epidermal layer. When the skin is exposed to UVB radiation (wavelength 290–315 nm), the following reaction occurs:
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UVB rays convert 7-dehydrocholesterol into previtamin D3.
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Previtamin D3 spontaneously isomerizes to vitamin D3 (cholecalciferol).
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Vitamin D3 enters the bloodstream and travels to the liver, where it undergoes further metabolic changes.
This is a mechanism that nature created as the basic source of vitamin D for humans – and it works very effectively, but only under appropriate conditions .
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2.2. What influences the effectiveness of skin synthesis?
📍 Latitude and time of year
In Poland and other countries north of the 37th parallel, from October to March UVB radiation is too weak to enable effective vitamin D synthesis. In practice, this means that for about half a year the body is unable to produce it in the skin – even if you are outdoors.
☀️ An hour in the day
The highest intensity of UVB radiation occurs between 10:00 a.m. and 3:00 p.m. Outside this time period, the angle of incidence of the sun's rays is too low, limiting their ability to penetrate the atmosphere.
⏱️ Exposure time and exposed skin area
For synthesis to be effective:
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15–30 minutes of sun exposure per day is enough (in spring and summer),
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it is best if larger parts of the body are exposed: arms, legs, neckline ,
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exposure to the face and hands is usually not enough to cover the daily requirement.
👩🏽🦱 Skin type
The darker the skin color (more melanin), the more difficult it is for UVB rays to reach the deeper layers of the epidermis:
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people with fair skin (phototype I-II) synthesize vitamin D faster,
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People with dark skin (phototype V-VI) need up to 3-5 times more time in the sun to achieve a similar effect.
🧴 Using sunscreen
Sunscreens, especially those with a high SPF (30+), can reduce vitamin D synthesis by up to 95–99% . Therefore, it's important to find a balance – short, daily exposure without sunscreen , followed by subsequent application, may be the optimal solution.
👕 Clothing and physical barrier
The natural barrier in the form of clothes, as well as staying in the shade, behind glass or indoors, completely prevents the synthesis of vitamin D - UVB rays do not penetrate glass.
👵 Age and skin condition
In older people, the amount of 7-dehydrocholesterol in the skin decreases significantly, which limits the ability to synthesize vitamin D. Therefore, seniors are one of the groups particularly vulnerable to deficiency .
Natural vitamin D synthesis is a brilliant mechanism, but it requires appropriate conditions and daily exposure to sunlight. Unfortunately, as we will soon demonstrate, in practice, many people are unable to afford this luxury.
3. How much sun is enough?
Although the human body can synthesize vitamin D on its own when exposed to UVB radiation, this doesn't mean that every sun exposure leads to optimal levels of this substance in the blood. Too little sun, too short an exposure time, or the wrong time of day can all result in insufficient vitamin D synthesis. On the other hand, excessive UV exposure is associated with a risk of skin damage. Therefore, finding a sensible balance is crucial.
3.1. General recommendations: how much and how long?
According to experts, to get your daily dose of vitamin D from sunlight:
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15 to 30 minutes of exposure per day is enough, depending on skin type.
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At least 20–25% of your body surface should be exposed – e.g., forearms, calves, and face.
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The best time is between 10:00 a.m. and 3:00 p.m. , when UVB radiation is most intense.
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Exposure should be without the use of sunscreen – but only for a short time and without the risk of burns.
During the spring and summer months, in sunny weather, this dose is usually sufficient to maintain normal vitamin D levels, provided that exposure is regular and daily .
3.2. Examples of daily exposure
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Walking in short sleeves and shorts for 20 minutes on a sunny day in June can provide up to 2,000–4,000 IU of vitamin D.
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Exposing only your face and hands is usually not enough to cover your daily needs.
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Lying on the beach for 1-2 hours won't significantly increase vitamin D production – the body limits its synthesis once a certain level is reached. Excess UV exposure only leads to skin damage.
3.3. Factors that reduce the efficiency of synthesis
Despite regular outdoor activities, many people do not achieve optimal vitamin D production . Common obstacles include:
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Exposure time too short.
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Wearing clothing that covers most of the body.
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Staying in the shade or behind glass.
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Using UV filters throughout the day.
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Being outdoors after 4pm – UVB rays are minimal then.
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Cloud cover, smog, high latitude.
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3.4. Is it possible to overdose on vitamin D from the sun?
This is one of the most common questions – and the answer is no , at least not under natural conditions. The body has an autoregulatory mechanism that stops vitamin D synthesis once a sufficient level is reached. Further UV radiation only leads to the breakdown of the excess vitamin precursor into inactive compounds.
However, overdose is only possible with excessive supplementation , so it is always worth following the recommendations and – if possible – testing the level of 25(OH)D in the blood.
Conclusion? Daily sun exposure is important and effective , but it must be properly planned. In practice, many of us fail to meet these requirements, especially during the fall and winter months, leading to serious deficiencies.
And that is why more and more experts recommend conscious supplementation , which we will discuss in more detail later in the article.
4. Why is natural synthesis not enough?
Although nature has equipped us with the ability to produce vitamin D on our own, the reality is that for many people, this source is simply insufficient . Numerous studies show that even during the summer, a significant percentage of the population has low levels of this crucial substance in their blood, and in the autumn and winter months, the situation is even more dramatic. Why is this happening?
4.1. Climate and geography
Poland, like most Central European countries, is located at a latitude that doesn't favor year-round vitamin D synthesis . From October to March, the angle of sunlight is too low for adequate UVB radiation to reach the earth's surface. During this period, regardless of the weather, the skin is unable to produce vitamin D , even with daily outdoor exposure.
4.2. Lifestyle and Deficiencies
Modern lifestyles further limit our exposure to the sun:
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We spend most of our time indoors – at work, at home, in the car.
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We travel mainly in the evenings or early mornings , avoiding the most effective time for synthesis.
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Clothing that covers the body , especially outside the summer season, significantly reduces the area of skin exposed to the sun.
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Fearing skin cancer, more and more people are using sunscreen every day , which – although justified – further reduces the production of vitamin D.
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4.3. Age, weight and skin type
Not every body produces vitamin D at the same rate:
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👵 Older people have significantly less 7-dehydrocholesterol in their skin, which reduces its ability to synthesize it.
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⚖️ Overweight and obese people tend to "store" vitamin D in fat tissue, making it less available in the bloodstream .
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🧑🏽🦱 People with darker skin need much more time in the sun to achieve the same effect as people with fair skin.
4.4. Shortages – a silent epidemic
According to research conducted in Poland and Central Europe:
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80–90% of the population is vitamin D deficient during the winter months .
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Even in summer, more than 50% of people do not reach the optimal level of 25(OH)D in the blood (i.e. the measurable form of this vitamin).
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Vitamin D deficiency is associated not only with the risk of osteoporosis, but also with:
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reduced immunity,
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greater risk of infection (e.g. flu, COVID-19),
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mood disorders and depression,
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cardiovascular diseases,
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muscle weakness and chronic fatigue.
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4.5. The Solution? Conscious Supplementation
Given the limitations resulting from climate, lifestyle and body physiology, conscious vitamin D supplementation becomes a necessity, not a choice – especially from September to April, and in some cases all year round.
Well-chosen supplementation allows you to:
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maintain vitamin D levels at an optimal level (30–50 ng/ml),
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support immunity and well-being,
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minimize the risk of chronic diseases and weakening of the skeletal system.
In the next part of the article, we will look at how to supplement vitamin D wisely and what products are worth choosing to supplement it effectively and safely.
5. Vitamin D supplementation – how, when and how much?
Given the limited ability of the skin to synthesize vitamin D—especially in autumn and winter— supplementation becomes an essential part of health care . But how can we do it wisely? In this chapter, we'll address the most common questions: who should supplement vitamin D, in what dose, when, and in what form.
5.1. Who should supplement?
In practice, almost everyone . According to the recommendations of Polish and European experts:
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Children and adolescents – from the first days of life to 18 years of age.
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Adults – year-round if their sun exposure is insufficient (and it usually is).
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Seniors (60–75 years old) and older people (75+) – absolutely all year round.
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Pregnant and breastfeeding women – as recommended by your doctor.
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People with obesity often need higher doses.
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People with dark skin, working indoors, avoiding the sun or using UV filters should also supplement all year round.
5.2. Recommended supplement doses
| Age group/health status | Daily dose (IU) |
|---|---|
| Newborns and infants (0–12 months) | 400–600 IU |
| Children (1–10 years) | 600–1000 IU |
| Youth (11–18 years old) | 800–2000 IU |
| Adults (19–65 years) | 800–2000 IU |
| Seniors (65+) | 800–2000 IU |
| Obese/deficient people | 1600–4000 IU, or even more – after medical consultation |
| Pregnant women | 1500–2000 IU (or as directed by your doctor) |
Note: The individual dose should be adjusted to the current level of 25(OH)D in the blood serum and the body's needs.
5.3. When and how to take vitamin D?
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🕓 It is best to take it in the morning or at noon , as vitamin D may have a stimulating effect - in some people, taking it in the evening may disturb sleep.
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🧈 Always with a meal containing fat - vitamin D is fat-soluble, so its absorption increases in the presence of e.g. avocado, olive oil , nuts , eggs, fatty fish.
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💊 The form of the supplement matters – vitamin D3 (cholecalciferol) in the form of:
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soft capsules (with oil) – high bioavailability,
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drops – convenient for children and the elderly,
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aerosol (spray) – rapid absorption through mucous membranes,
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tablets – slightly less effective if not taken with fats.
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Vitamin D3+K2 drops 30 ml - Aura Herbals
5.4. How to check your vitamin D level?
It is recommended to determine the level of 25(OH)D in blood serum – this is the most accurate indicator of the body's vitamin D supply.
Here is a general interpretation of the results:
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< 20 ng/ml – deficiency
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20–30 ng/ml – insufficient level
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30–50 ng/ml – optimal level
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50–100 ng/ml – high level
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> 100 ng/ml – risk of toxicity (very rare with standard supplementation)
It is worth doing the test at least once a year – preferably in autumn or after the end of the summer season.
5.5. Is supplementation safe?
Yes – if recommended doses are followed . Vitamin D can only be toxic in very large amounts, exceeding 10,000 IU per day for prolonged periods , which in practice is extremely rare. By using preventative doses appropriate for age and body weight, the risk of side effects is minimal .
5.6. What should you pay attention to when choosing a supplement?
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💡 Vitamin form – choose products with vitamin D3 (not D2).
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🧪 Contents – make sure your daily dose meets your needs.
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✅ Quality and safety certificates – choose products from proven manufacturers, laboratory tested.
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🌿 Ingredients – it is worth choosing pure ingredients without artificial additives, especially in the case of children and people with allergies.
6. Summary
Although often underestimated, vitamin D plays a crucial role in maintaining the health of the entire body —from skeletal system and immunity to mental and cardiovascular health. Our bodies are designed to obtain it primarily from sunlight, but the realities of climate, lifestyle, and individual physiology mean that most of us are unable to obtain sufficient amounts of this vitamin through natural skin synthesis alone .
Regular testing and preventive care, including informed supplementation , are essential tools today to ensure proper levels of vitamin D in the body. It's a small step that can bring enormous health benefits – improved well-being, increased immunity, stronger bones, and protection against many chronic diseases.
Therefore, regardless of the season, age or lifestyle, it is worth taking care of this important vitamin every day .
Take care of yourself – and don't forget that sometimes all it takes is a few minutes in the sun, good food, and a properly selected supplement to do a lot for your health.
