Vitamin D deficiency is common in northern Europe because for about half the year the sun sits too low for your skin to make much vitamin D. You cannot tell your level from how you feel. A blood test for 25(OH)D is the only way to know, and a doctor is the right person to read it.
If you decide to take a supplement, the European Food Safety Authority (EFSA) sets the adequate intake for adults at 15 µg (600 IU) a day and the tolerable upper level at 100 µg (4000 IU) a day from all sources combined.
Why vitamin D runs low at northern latitudes
Your skin makes vitamin D when ultraviolet B (UVB) light reaches it. How much UVB gets through the atmosphere depends on the angle of the sun. Vilnius lies at about 54.7° north, Riga at 56.9° and Tallinn at 59.4°. At these latitudes, from roughly October to March, the sun stays so low that skin makes little or no vitamin D, even on a clear day.
Summer helps, but less than people expect. Office work, clothing, sunscreen and cloudy weeks all cut the amount of UVB your skin actually gets. The body keeps some vitamin D from summer in fat tissue and the liver, and those stores run down over the winter.
Food covers only part of the need. Oily fish such as herring, salmon and mackerel, egg yolks and foods with added vitamin D are the main sources. Most people do not eat oily fish often enough to rely on it.
Some groups have more reason to ask their doctor about a test:
- older adults, because skin makes less vitamin D with age;
- people who spend little time outdoors or keep most of their skin covered;
- people with darker skin;
- people on a vegan diet without fortified foods;
- people with a higher body weight;
- babies who are breastfed (ask your paediatrician what they need).
The only way to know: a 25(OH)D blood test
Many websites publish lists of signs that supposedly point to low vitamin D. Such lists are useless for self-diagnosis. The signs people link to low vitamin D are common and have plenty of other causes, and low levels often cause nothing you would notice at all.
The test measures 25-hydroxyvitamin D, written 25(OH)D. It is the form that circulates in your blood and reflects what you get from the sun, food and supplements together. You can ask your GP for it or order it at a private laboratory. Results come in either nmol/L or ng/mL. To convert, multiply ng/mL by 2.5.
| 25(OH)D, nmol/L | ng/mL | How the NIH Office of Dietary Supplements describes it |
|---|---|---|
| below 30 | below 12 | associated with vitamin D deficiency |
| 30 to 50 | 12 to 20 | generally considered inadequate for bone and overall health |
| 50 or more | 20 or more | adequate for most people |
| above 125 | above 50 | linked to potential adverse effects |
Laboratories and national guidelines use slightly different ranges. Let your doctor interpret the result, choose the dose and decide when to repeat the test. Do not start high doses on your own after a low result.
IU and µg: how to read a vitamin D label
Labels give vitamin D in micrograms (µg), often with international units (IU) in brackets. The conversion is fixed: 1 µg equals 40 IU. The percentage of NRV on EU labels is calculated against 5 µg, which is why a 50 µg capsule shows 1000 %.
| µg | IU | What the amount means |
|---|---|---|
| 5 µg | 200 IU | 100 % of the NRV used on EU labels |
| 15 µg | 600 IU | EFSA adequate intake for adults and children from 1 year |
| 25 µg | 1000 IU | a common daily supplement dose |
| 50 µg | 2000 IU | half of the adult upper level |
| 100 µg | 4000 IU | EFSA tolerable upper level for adults and teenagers from 11 |
| 1250 µg | 50 000 IU | 12.5 times the daily upper level; only on a doctor's instructions |
OstroVit
Vitamin D3, 2000 IU, 60 SoftgelsHow much vitamin D per day: EFSA values
EFSA sets an adequate intake of 15 µg (600 IU) a day for adults, including during pregnancy and breastfeeding, and for children and teenagers from 1 to 17 years. For babies aged 7 to 11 months the value is 10 µg. EFSA set these numbers for conditions where the skin makes little vitamin D, which matches a Baltic winter.
The tolerable upper intake level is the highest daily amount that is unlikely to cause harm over a long period. In 2023 EFSA set it at 100 µg (4000 IU) for adults and teenagers from 11 years, and 50 µg (2000 IU) for children aged 1 to 10. The upper level counts everything together: supplements, fortified foods and multivitamins. It is a ceiling, not a target.
Add up every product you take. A multivitamin with 25 µg plus a fish oil with 10 µg plus a separate D3 capsule can reach the upper level faster than you think.
Two label details are worth knowing. Some 4000 IU products state on the label that they are intended for adults over 75, so read the label before you buy the strongest pack. Products with 50 000 IU per capsule also exist. One such capsule holds 12.5 times the daily upper level, so this strength belongs only in a plan your doctor sets, including how often to take it.
For children, ask the paediatrician or family doctor which dose fits the child's age, and remember the lower upper level of 50 µg for ages 1 to 10.
D3 or D2: which form to choose
Supplements contain one of two forms. Vitamin D3 (cholecalciferol) is the form your skin makes. In supplements it usually comes from lanolin in sheep's wool, or from lichen in vegan products. Vitamin D2 (ergocalciferol) is made from yeast or mushrooms exposed to UV light.
| Vitamin D3 (cholecalciferol) | Vitamin D2 (ergocalciferol) | |
|---|---|---|
| Source in supplements | lanolin, or lichen in vegan products | yeast or mushrooms treated with UV light |
| Effect on blood 25(OH)D | raises it more and for longer, according to NIH ODS | also raises it, but less |
| Suitable for vegans | only the lichen version | yes |
For most people D3 is the practical choice. If you avoid animal products, look for D3 from lichen.
Vitamin D with K2
Many products combine vitamin D3 with vitamin K2, usually as menaquinone-7 (MK-7). The two vitamins have their own authorised claims. Vitamin D contributes to the maintenance of normal bones. Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus. Vitamin K contributes to the maintenance of normal bones. A combined tablet simply means one product instead of two.
Vitamin D has other authorised roles as well. Vitamin D contributes to the normal function of the immune system. Vitamin D contributes to the maintenance of normal muscle function.
If you take an anticoagulant that works as a vitamin K antagonist, such as warfarin or acenocoumarol, do not take products with vitamin K unless your doctor approves. Vitamin K affects how these medicines work.
How to take vitamin D so it is absorbed
Vitamin D is fat-soluble, so your body absorbs it better with a meal that contains some fat. Softgel capsules already come dissolved in oil. With tablets, take them with your main meal rather than with a coffee on an empty stomach. If your product's label gives a different instruction, follow the label.
The time of day matters less than doing it every day. Pick a meal you never skip and take it then.
Keep the pack next to whatever you use at that meal, such as the bread box or the coffee machine. A daily dose you remember beats a perfect schedule you forget.
How to choose a vitamin D supplement
- Get a 25(OH)D test and talk the result through with your doctor, especially if you are pregnant, take medication or want a dose above 25 µg.
- Check the amount per daily dose in µg, not per pack.
- Add up vitamin D from all your products and keep the total under 100 µg a day unless your doctor says otherwise.
- Choose D3. If you are vegan, pick D3 from lichen.
- Take a product with K2 only if you are not on vitamin K antagonist anticoagulants.
- Read the age group on the label: some 1000 IU products are for adults up to 75, some 4000 IU products for adults over 75.
- Compare price per day: a pack of 120 one-a-day capsules lasts four months.
You can compare doses and forms side by side in the vitamin D collection.
OstroVit
Vitamin D3, 4000 IU, 120 SoftgelsFAQ
How do I know if I have vitamin D deficiency?
Only a blood test for 25(OH)D shows it. The signs often linked to low vitamin D are common and have many other causes, so a list of symptoms cannot replace the test. Ask your GP or a private laboratory.
Is 4000 IU of vitamin D too much?
4000 IU is 100 µg, which equals EFSA's tolerable upper level for adults. It is the maximum from all sources combined, not a recommended dose. Some 4000 IU products are labelled for adults over 75. Discuss this dose with your doctor first.
How much vitamin D should I take in winter?
EFSA's adequate intake for adults is 15 µg (600 IU) a day, set for low sun exposure. If your test shows a low level, your doctor may suggest a different dose for a set period and a repeat test afterwards.
What does 50,000 IU of vitamin D mean?
It is 1250 µg in a single capsule, 12.5 times the daily upper level. Such strengths are taken only on a doctor's instructions, usually on a weekly or other spaced schedule the doctor sets.
When is the best time to take vitamin D?
With a meal that contains some fat, at the same time every day. Morning or evening makes little difference. Follow your product's label if it says otherwise.
Should I take vitamin D all year round?
That depends on your test result, diet and how much time you spend outside in summer. Many people in the Baltics take it from autumn to spring. Your doctor can advise after a test.
You will find D3 alone and D3 with K2 in our vitamin D range.
Sources
- EFSA (2016): Dietary reference values for vitamin D
- EFSA (2023): Scientific opinion on the tolerable upper intake level for vitamin D
- NIH Office of Dietary Supplements: Vitamin D fact sheet for health professionals
- Commission Regulation (EU) No 432/2012 on permitted health claims
Content reviewed by Inese Kalniņa, dietitian.
