Written by the Plenthera team (orthomolecularly trained). Scientifically reviewed in April 2026. Last updated: April 30, 2026.
Vitamin D is perhaps the most discussed micronutrient of the past decade. The body produces it itself via the skin when exposed to UVB sunlight, but in the Netherlands, for most of the year, the sun is at too low an angle for effective production. At Plenthera, you'll find vitamin D in all relevant dosages and forms: D3 drops for flexibility, capsules for convenience, and combination products with K2 for optimal synergy. EFSA-approved for bones, muscles, and the immune system.
Which vitamin D is right for you?
| Form | Dosage | Best for | Special feature |
|---|---|---|---|
| D3 capsules | 25-100 µg | Daily use for adults | Simple, in oil |
| D3 drops | Flexible dosing | Children, elderly, dosage fine-tuning | Under the tongue |
| D3 + K2 | 25-75 µg D + 50-100 µg K2 | Bone and vascular health | Synergy K2 directs calcium |
| Vegan D3 (lichen) | 25-75 µg | Vegan diet | Plant-based, equally effective |
| Cod liver oil | Variable | Winter, traditional source | With vitamin A and omega 3 |
What is vitamin D?
Vitamin D is a fat-soluble vitamin that the body can produce itself via the skin when exposed to UVB sunlight. It effectively functions as a hormone and plays a role in calcium absorption, bones, muscles, teeth, and the immune system.
Strictly speaking, vitamin D is not a classic vitamin, but a steroid hormone precursor. When UVB light (wavelength 290-315 nm) hits the skin, 7-dehydrocholesterol is converted to pre-vitamin D3, which then spontaneously isomerizes to vitamin D3 (cholecalciferol). In the liver, this is converted to 25(OH)D — the form measured in blood tests — and in the kidneys to calcitriol, the active hormonal form.
In the Netherlands, from October to April, the sun is at too low an angle for significant production. In addition, many people spend little time outdoors, wear concealing clothing, or have a skin type that produces pigment more efficiently (which slows down production). The Dutch Health Council therefore advises supplementation for specific groups: 10 µg for people with little sun exposure, and 20 µg for those aged 70+ and pregnant women.
Vitamin D has two important "partners" in its function: magnesium and vitamin K2. The activation of vitamin D in the liver and kidneys is dependent on magnesium-containing enzymes — thus, a low magnesium status inhibits the action of vitamin D. Vitamin K2 directs the calcium absorbed by vitamin D to the correct destination (bones and teeth). Check out our magnesium category and vitamin K category for the combinations.
Vitamin D and EFSA — what is scientifically recognized?
Vitamin D has an extensive range of recognized EFSA claims, included in EU Regulation 432/2012. The following formulations may be used literally — provided the threshold is met:
"Vitamin D contributes to the normal absorption/utilisation of calcium and phosphorus."
"Vitamin D contributes to normal blood calcium levels."
"Vitamin D contributes to the maintenance of normal bones."
"Vitamin D contributes to the maintenance of normal muscle function."
"Vitamin D contributes to the maintenance of normal teeth."
"Vitamin D contributes to the normal function of the immune system."
"Vitamin D has a role in the process of cell division."
"Vitamin D is needed for normal growth and development of bone in children."
Threshold: claims apply for a daily intake that provides at least 15% of the RI — which is 0.75 µg of vitamin D per serving. Our products usually deliver significantly more than this threshold, in the range of 25-100 µg per dose.
The magnesium puzzle piece — why a D supplement without magnesium can be suboptimal
The activation of vitamin D involves a chain of enzymatic steps, several of which require magnesium as a cofactor. A low magnesium status can therefore explain why some people do not achieve optimal 25(OH)D blood levels despite vitamin D supplementation.
Research (including studies by Reddy & Edwards in Am J Therapeutics) points to an interaction: sufficient magnesium supports vitamin D metabolism, and vitamin D in turn supports mineral balance. For those who want to maximize the benefits of a vitamin D supplement, a healthy magnesium intake is a logical addition.
Check out our magnesium category for common forms (bisglycinate, citrate, malate) and choose the form that suits your daily profile.
The vitamin D forms at Plenthera
Vitamin D3 capsules
The most common form: a softgel or capsule with vitamin D3 in oil, for optimal absorption. Available in dosages from 25 µg (1000 IU) to 100 µg (4000 IU). Suitable for those who prefer to take pills over drops.
Vitamin D3 drops
For those who don't want pills or want to adjust dosages: vitamin D in MCT or olive oil. One drop under the tongue or with a meal. Ideal for children, the elderly, and those who want flexible dosing.
Vitamin D3 + K2
The synergy form. Vitamin K2 activates proteins (osteocalcin, matrix-Gla-protein) that direct calcium to bones and teeth. The D3+K2 combination is chosen by many for bone and cardiovascular health.
Vegan Vitamin D3 (from lichen)
D3 — previously only available from animal sources — is now also produced plant-based from lichen. Effective and plant-based. Also check out our supplements for vegans.
Cod liver oil (D + A + omega 3)
A traditional source that provides vitamin A and omega 3 in addition to vitamin D. Popular in winter — also see our omega 3 category for more information.
How to use vitamin D?
Simple basic approach to vitamin D:
- Determine your needs based on age, sun exposure, and diet.
- For most adults, 25-50 µg (1000-2000 IU) D3 per day is a safe baseline.
- For specific groups (70+, pregnant women) or in cases of proven deficiency: 50-100 µg per day.
- Take vitamin D with a meal containing some fat — fat-soluble, so absorption-dependent.
- Combine with sufficient magnesium intake for optimal activation.
- Consider vitamin K2 for the bone and cardiovascular pathway — especially with higher D3 dosages.
- If in doubt or for long-term use, have your 25(OH)D blood level tested (optimum often 75-125 nmol/L).
Myths and misconceptions about vitamin D
Myth 1: "You don't need to take vitamin D in summer."
For some, that's true — those who spend a lot of time outdoors with uncovered skin can produce enough in summer. But in the Netherlands, even in July, the sun is not at the right angle all day, sunscreen blocks UVB, and many people stay indoors during the day. A blood value measurement at the end of summer will provide clarity.
Myth 2: "Vitamin D2 is just as good as D3."
D3 (cholecalciferol) increases 25(OH)D blood levels significantly more effectively than D2 (ergocalciferol) at the same dosage. Therefore, D3 is the preferred form for supplementation — including plant-based D3 from lichen for vegans.
Myth 3: "The more vitamin D, the better."
Vitamin D is fat-soluble — overdosing is possible. The NVWA and EFSA set an upper limit of 100 µg per day for long-term intake. Above that limit, hypercalcemia (too much calcium in the blood) is a possible risk. Standard dosages (25-50 µg) are well within the safe range.
Myth 4: "A light therapy lamp works just as well as sun or supplements."
A regular "daylight" lamp does not produce UVB and does not contribute to vitamin D production. Special UVB lamps can, but are expensive and require careful use. For most people, a supplement is more practical and safer.
Combining Vitamin D with other supplements
Vitamin D works synergistically with various other nutrients. Popular combinations:
- Vitamin K2: directs calcium to bones and teeth instead of soft tissues — especially relevant with higher D3 dosages.
- Magnesium: cofactor in the activation of vitamin D. A low magnesium status inhibits the effectiveness of D supplementation.
- Calcium: vitamin D increases calcium absorption. For those focusing primarily on bones, calcium + D3 + K2 is a logical trio.
- Omega 3 (cod liver oil): natural combination — cod liver oil naturally provides D, A, and omega 3.
- Multivitamin: for those who want complete coverage without separate supplements.
Frequently Asked Questions
What is vitamin D?
Vitamin D is a fat-soluble vitamin that the body produces itself via the skin when exposed to UVB sunlight. It plays a role in calcium absorption, bones, muscles, and the immune system.
What is the difference between D2 and D3?
D2 (ergocalciferol) is plant-based, D3 (cholecalciferol) is animal-derived or from lichen (vegan). D3 is more effective in increasing blood 25(OH)D levels and is therefore the preferred form.
How much vitamin D per day?
EU-RI: 5 µg. The Dutch Health Council advises 10 µg for people with little sun exposure and 20 µg for those aged 70+ and pregnant women. EFSA upper limit: 100 µg/day for adults.
When to take vitamin D?
With a meal containing some fat for optimal absorption. Morning or afternoon is slightly preferred — some people experience a slightly alerting effect in the evening.
What does vitamin K2 do with vitamin D?
D increases calcium absorption; K2 activates proteins that direct calcium to bones and teeth, instead of soft tissues. The combination is often chosen for bone and cardiovascular health.
Do you need magnesium with vitamin D?
Magnesium is a cofactor in the activation of vitamin D. A low magnesium status inhibits the action of D supplementation — sufficient magnesium intake is therefore logical.
Vitamin D for children — how much?
Children aged 0-4 years: 10 µg per day (Health Council). If in doubt, ask your consultation bureau or doctor for advice.
What are vitamin D deficiency symptoms?
Possible signs: fatigue, muscle weakness, frequent colds, bone pain, depressed mood. No single symptom is conclusive; a 25(OH)D blood test provides clarity.
Do you need vitamin D in summer too?
Many people get enough production from the sun in summer (May-September). With concealing clothing, dark skin, little time outdoors, or sunscreen >SPF 15, supplementation remains useful.
Is vegan vitamin D3 available?
Yes. Plant-based D3 is extracted from lichen and is as effective as animal D3. Suitable for vegans and pescatarians.
Sources
- EFSA Regulation (EU) 432/2012 — vitamin D claims.
- EFSA NDA Panel — Scientific Opinion on Tolerable Upper Intake Level for vitamin D (2012).
- Dutch Health Council — Dietary reference values for vitamin D (2012).
- Reddy P. & Edwards LR., "Magnesium Supplementation in Vitamin D Deficiency", Am J Therapeutics (2019).
- Holick MF., "Vitamin D Deficiency", N Engl J Med (2007).
- RIVM — food consumption studies on vitamin D status of the Dutch population.
Disclaimer: This text is intended for informational purposes only and does not replace medical advice. Vitamin D is a dietary supplement, not a medicine. In case of doubt or if you are taking medication, we recommend consulting a doctor or orthomolecular therapist first.