Vitamin D
D3 or D2, micrograms or IU, with K2 or without: how to make sense of vitamin D, how much supplements contain and how to choose.
- Vitamin D contributes to normal absorption and 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 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.
The claims apply to a product whose daily dose provides at least 15 % of the reference intake (5 µg).
A varied and balanced diet and a healthy lifestyle are important.
What it is
Vitamin D is a fat-soluble vitamin. The skin makes it under the sun's UV light; from food it comes mainly from oily fish, egg yolk and fortified products. In Estonia and Finland there is too little sun for this from October to March, which is why vitamin D is one of the region's best-selling supplements.
Vitamin D has authorised claims in the European Union — they are listed above. They apply to products whose daily dose provides at least 15 % of the reference intake (5 µg), that is at least 0.75 µg.
IU and micrograms
Vitamin D is stated either in micrograms (µg) or in international units (IU). The conversion is simple: 1 µg = 40 IU. So 25 µg is 1000 IU, 50 µg is 2000 IU and 100 µg is 4000 IU.
EFSA's tolerable upper intake level for adults is 100 µg (4000 IU) a day from all sources. High-dose supplements should not be combined with each other.
D3, D2 and D3 with K2
Vitamin D3 (cholecalciferol) is the form the skin makes; in supplements it usually comes from lanolin in sheep's wool, and vegan D3 from lichen. Vitamin D2 (ergocalciferol) is plant-derived and less common.
Many products pair D3 with vitamin K2 (menaquinone, MK-7). Vitamin K has its own authorised claims in the EU; they show on a product when the K2 dose is enough. People on blood-thinning medicines must ask a doctor before taking vitamin K.
How it is taken
Vitamin D is fat-soluble, so capsules and drops are usually taken with a meal that contains some fat. Oil-filled capsules are convenient; drops allow exact dosing. Take the dose on the pack and count the vitamin D in any multivitamin you take at the same time.
How to choose
Decide on the dose in µg or IU, then the form (capsules, tablets, drops, spray) and whether you want K2. Vegans should look for D3 from lichen. Compare the price per daily dose: a tub of 365 capsules at 25 µg often beats 60 capsules at 100 µg if you need the smaller dose.
Frequently asked questions
How many IU are in 1 µg of vitamin D?
40 IU. For example 25 µg = 1000 IU, 50 µg = 2000 IU, 100 µg = 4000 IU.
How is D3 different from D2?
D3 (cholecalciferol) is the same form the skin produces; D2 (ergocalciferol) is plant-derived. Supplements more often use D3.
Is there vegan vitamin D3?
Yes, D3 from lichen is suitable for vegans. Ordinary D3 comes from lanolin in sheep's wool: vegetarian, but not vegan.
Can I take too much?
Yes. The upper level for adults is 100 µg (4000 IU) a day from all sources. Do not combine several high-dose supplements, and follow the pack's directions.
When is the best time to take vitamin D?
With a meal containing fat: vitamin D is fat-soluble. The time of day matters less.
Do I need vitamin D in summer?
That is for you and your doctor; in summer the skin makes more, so many take it from autumn to spring.
Can children take vitamin D?
There are separate products and doses for children. Agree children's doses with a doctor.
How do I know my dose?
Most reliably from a blood test and a doctor's advice; the pack gives the maker's dose.
Vitamin D & K2 in the shop
