In short:
- In Estonia’s climate, the sun does not provide enough vitamin D synthesis in the skin from October to April.
- The amount of vitamin D you get from food usually falls short of the recommended daily dose.
- A vitamin D3 supplement is the most reliable proven way to maintain a normal level.
- The EFSA recommended daily dose for adults is 15 µg (600 IU), often up to 20–25 µg in winter.
Vitamin D sources are a topic that concerns most people in Estonia – especially in the winter months, when sunlight is scarce. Comparing the three main sources – food, sun and supplements – helps you make an informed choice to keep your body healthy all year round. In this article, we look at each vitamin D source in light of the research.
What are the main vitamin D sources and how do they differ?
Vitamin D sources fall into three categories: sunlight-driven synthesis in the skin, vitamin D from food, and supplements. Although vitamin D is a fat-soluble vitamin that the body can make itself, its production depends heavily on geographic location, season and skin type (Holick, 2007).
In Estonia, the sun sits too low in the sky in autumn and winter for UVB radiation to synthesize enough vitamin D in the skin. This means that for about half the year, our main vitamin D sources are food and supplements.
How much vitamin D can you realistically get from food?
Food offers limited ways to get vitamin D, because it occurs naturally in only a few foods:
| Food | Amount of vitamin D |
|---|---|
| Herring (100 g) | ~16 µg (640 IU) |
| Salmon (100 g) | ~11 µg (440 IU) |
| Mackerel (100 g) | ~8 µg (320 IU) |
| Egg (1 pc) | ~1.1 µg (44 IU) |
| Whole milk (100 ml) | ~0.03 µg (1.2 IU) |
| Fortified milk (100 ml) | ~1.2 µg (48 IU) |
If you eat fatty fish several times a week, food is a meaningful vitamin D source. However, a Europe-wide study showed that the average European gets only 3–4 µg of vitamin D a day from food – far from the recommended 15 µg (Cashman et al., 2016). This applies to people in Estonia as well.
Like vitamin B and vitamin C, vitamin D has a wide range of functions in the body – from the immune system to bone health – which makes adequate intake especially important.
Does the sun provide enough vitamin D in Estonia?
Sunlight is the most natural vitamin D source: UVB radiation triggers the synthesis of vitamin D3 from 7-dehydrocholesterol in the skin. In summer (May–September), a person in Estonia can cover their needs with 15–30 minutes of daily sun exposure. The optimal conditions are:
- Time of day: 11:00–15:00
- Exposed skin: forearms and legs bare in the sun
- Skin protection: no SPF cream (sunscreen blocks UVB radiation)
From October to April, however, the UVB angle at Estonia’s latitude (58–60°N) is too low – virtually no vitamin D is synthesized from sunlight (Holick et al., 2011). For this reason, the sun cannot be considered a year-round vitamin D source in Estonia’s climate.
In addition, synthesis is affected by skin pigmentation (darker skin needs longer), age (older people synthesize less) and BMI (body fat sequesters the vitamin out of circulation).
How do supplements compare with other vitamin D sources?
Supplements are the most reliable way to manage your vitamin D level. Studies clearly show that vitamin D3 (cholecalciferol) raises blood 25(OH)D levels considerably more effectively than vitamin D2 (ergocalciferol) (Tripkovic et al., 2012). According to dose-response studies, every 100 IU of vitamin D3 added to the daily diet raises serum 25(OH)D concentration by roughly 1–2 nmol/l (Heaney et al., 2003).
The NIH Office of Dietary Supplements points out that for adults who experience a seasonal shortfall in winter, using a D3 supplement at 1500–2000 IU (37.5–50 µg) per day is justified.
Advantages of supplements over other vitamin D sources:
– Precisely known dose
– Year-round availability
– Independent of weather and skin type
– Reliable clinical evidence
D2 vs D3 – which supplement is more effective?
Vitamin D comes in supplements in two forms: D2 (plant-based, suitable for vegans) and D3 (usually from lanolin, i.e. sheep’s wool fat, but also available in a vegan form made from lichen). Studies confirm that D3 raises and maintains blood levels more effectively than the same dose of D2 (Tripkovic et al., 2012).
| Property | D3 (cholecalciferol) | D2 (ergocalciferol) |
|---|---|---|
| Origin | Animal/lichen | Plant/fungus |
| Bioavailability | Higher | Lower |
| Duration of effect | Longer | Shorter |
| Suitable for vegans | Lichen-based version | Yes |
| Price | Moderate | Moderate |
References
- Holick MF. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3):266–281. PMID: 17634462
- Tripkovic L et al. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition, 95(6):1357–1364. PMID: 22552031
- Cashman KD et al. (2016). Vitamin D deficiency in Europe: pandemic? American Journal of Clinical Nutrition, 103(4):1033–1044. PMID: 26864360
- Holick MF et al. (2011). Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism, 96(7):1911–1930. PMID: 21646368
- Heaney RP et al. (2003). Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. American Journal of Clinical Nutrition, 77(1):204–210. PMID: 12540414
Frequently asked questions
When should you take a vitamin D supplement?
In Estonia, a vitamin D supplement is recommended from October to April, when the sun doesn’t provide enough. Many experts recommend taking it year-round, especially if you spend little time outdoors or have a darker skin type.
What is the recommended daily dose of vitamin D for adults?
EFSA recommends 15 µg (600 IU) a day for adults. The Estonian Nutrition Council recommends up to 20 µg in winter. The safe upper limit is 100 µg (4000 IU) a day, which should not be exceeded in the long term.
Is it possible to overdose on vitamin D from the sun?
No. The skin regulates vitamin D synthesis on its own, and any excess is broken down through photodegradation. An overdose from supplements is theoretically possible, but it takes a very long period of high-dose intake.
Does fatty fish cover your daily vitamin D requirement?
100 g of salmon contains roughly 11 µg of vitamin D, which covers about 70% of the daily dose. Eating fatty fish every day is a considerable source, but most people don’t eat fish that regularly.
How can you tell whether your vitamin D level is normal?
A blood 25(OH)D concentration of 50–125 nmol/l is considered optimal. Deficiency is defined as a level below 30 nmol/l. To check your level, you need a blood test through your family doctor – it’s especially advisable at the end of winter.
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