Buying vitamin D: an overview of forms, dosage, and selection criteria
In short, vitamin D is a fat-soluble prohormone that the body makes itself when it gets enough sunlight. In Central Europe, UVB radiation is generally insufficient to meet requirements, especially from October to March. Vitamin D supplements are available in D2 and D3 forms, as well as in drops, capsules, or tablets, with dosages ranging from 800 IU to 20,000 IU. The German Nutrition Society (DGE) recommends an intake of 800 IU (20 µg) per day if the body is unable to produce it naturally.
What is vitamin D?
- Despite its name, vitamin D isn't a traditional vitamin but a prohormone: the body can make it itself in the skin when exposed to sunlight (UVB).
- It's fat-soluble, so it's best absorbed when taken with a fatty meal or drink.
- The body usually meets most of its needs through sunlight; only a small amount can be obtained from food.
- Vitamin D levels in the blood are measured by the 25(OH)D (calcidiol) value.
Vitamin D2 vs. Vitamin D3: The difference
Characteristic | Vitamin D2 (ergocalciferol) | Vitamin D3 (cholecalciferol) |
|---|---|---|
Origin | Plant-based sources, such as mushrooms and yeast | Animal sources (e.g., lanolin) or plant-based sources from lichens |
Suitable for vegans | Yes | Only for lichen-based products |
Bioavailability | Considered less stable in blood levels | Considered the form found in the body, with a more stable duration of action |
Prevalence in dietary supplements | Less common | The most commonly used form |
A comparison of dosage forms
Form | Composition | Special features |
|---|---|---|
Drops | Vitamin D dissolved in a carrier oil (e.g., sunflower or olive oil) | Individually dosable, also suitable for infants and children |
Capsules | Vitamin D in oil, enclosed within a capsule shell | Fixed dosage per capsule, with no taste |
Tablets | Vitamin D in a solid matrix, sometimes with excipients | Easy to dose, longer shelf life |
Lozenges | Vitamin D that melts in your mouth | An alternative for those who find it difficult to swallow capsules or tablets |
Intake recommendations
Information on daily requirements varies depending on the source:
- DGE (German Nutrition Society): 800 IU (20 µg) per day when there is no endogenous production, as an estimate for an adequate intake.
- EFSA (European Food Safety Authority): Tolerable Upper Intake Level (UL) of 4,000 IU (100 µg) per day for adults.
- High-dose supplements (10,000–20,000 IU): In practice, these are sometimes used as a weekly dose or for short-term use, usually after consulting a doctor or based on a measured blood level.
The appropriate dosage for each individual depends on factors such as body weight, sun exposure, skin pigmentation, age, and current blood levels. A blood test is the only reliable way to determine your vitamin D levels.
What to consider when buying
- Dosage per serving: Check if it's given in IU (International Units) or µg (1 µg = 40 IU) and compare this to your desired daily dose.
- Carrier for drops/capsules: The type of oil used (e.g., olive, coconut, MCT, or sunflower oil) affects taste and how well it is tolerated.
- Additives: The number and type of excipients, colourants, and preservatives vary depending on the manufacturer.
- Combination supplements: Some products also contain vitamin K2, magnesium, or calcium – useful for those who want to get multiple nutrients at once.
- Origin (D2 vs. D3): For vegan diets, plant-based D3 supplements (from lichens) or D2 supplements are relevant.
- Certifications: Organic seals, laboratory analyses, or Veganz/V-Label certifications can guide your selection.
Who often considers taking supplements?
According to specialist literature, the following groups consider supplementation more often than average or statistically have lower blood levels more frequently:
- People who get little sun exposure (e.g., those who mainly work indoors)
- People living in northern latitudes, especially during the autumn and winter months
- Older people (the skin's natural synthesis declines with age)
- People with darker skin pigmentation
- People who mostly cover their skin
- Infants (for rickets prevention, as recommended by a doctor)
- Pregnant and breastfeeding women (in consultation with a doctor)
According to the DGE, it is estimated that a significant proportion of the German population has blood levels below the reference range defined by the DGE during the winter months.
Note: This text is for general information only and does not replace individual medical or nutritional advice. Information on dosages and reference values is based on publicly available recommendations from the DGE and EFSA and is subject to change.
Frequently Asked Questions About Vitamin D Supplements
1 µg of vitamin D is equivalent to 40 IU (International Units). For example: 20 µg = 800 IU.
Both forms increase blood levels. Studies show that D3 is more often linked to a more stable and longer-lasting increase in blood levels than D2. D3 supplements made from lichen are now also available for vegan diets.
Through a blood test that measures the level of 25(OH)D (calcidiol). Professional societies define reference ranges differently.
Since vitamin D has a half-life of several weeks in the blood, both daily and weekly intake schedules are common. The choice depends on the specific supplement and individual recommendations.
All three forms contain vitamin D in different carrier systems. Drops and capsules contain vitamin D dissolved in oil, while tablets use a solid matrix. The choice is usually based on preference, age, and the ability to swallow.
Vitamin D ensures healthy bones and is involved in a variety of metabolic processes in the human body. In contrast to all other vitamins, the need can't be met through nutrition alone; and a lack of the vitamin can cause serious illnesses. An adequate supply of vitamin D is therefore important.
Different organizations recommend varying doses of vitamin D. For example, in cases where vitamin D formation through sunlight is deficient, the DGE currently recommends a dose of 400 IU for infants up to 1 year of age and 800 IU for children, adolescents, adults, seniors, and pregnant and nursing women.
According to vitamin D experts this recommendation is too low and only represents the minimum daily intake required to stave off rickets.
You can measure your vitamin D levels by using a blood test to determine if you have enough vitamin D in your body. In fact, not the active form of vitamin D is measured, but the concentration of 25(OH)D (25-hydroxyvitamin D) in the blood.
The 25 (OH)D value is a precursor of vitamin D, in which form is is transported in the blood. If necessary, this form is converted into the active form of vitamin D (calcitriol).
The 25 (OH)D value shows how much vitamin D you got through nutrition or produced during sun exposure. But this value does not tell you anything about your vitamin D levels throughout the year, which will vary depending on the sun exposure and vitamin D uptake from food.
The half-life of 25(OH) Vitamin D is 2 month. This means, that the vitamin D level will fall to half of its value, provided that you no longer get any vitamin D at all.
Recent studies suggest that both vitamin D3 and vitamin K2 may play an important role in bone and arterial health. Insufficient intake of both vitamins is widespread among the Western population—which is why more and more people are taking vitamin D3 and K2 daily as dietary supplements.
According to current scientific knowledge, anyone who regularly takes vitamin D3 supplements should also consume sufficient amounts of vitamin K2. In this guide, we explain why this is the case, what dosages the EFSA recommends, and how you can optimally combine both vitamins.
⚠️ Important note: The content of this article is for informational purposes only and is not a substitute for medical advice, diagnosis, or treatment. Dietary supplements are not a substitute for a balanced, varied diet and a healthy lifestyle. Please always consult a doctor or pharmacist regarding health questions or the use of medications. |