Vitamin D3

Vitamin D3, or cholecalciferol, is the same form of vitamin D your skin makes from summer sunlight. It is fat-soluble, which means it needs a little fat in your gut to be absorbed properly. In the UK, sunlight from October to early March is too weak for your skin to make vitamin D, so this is the point in the year when most people start looking at a supplement.

Vitamin D contributes to the normal function of the immune system, to the maintenance of normal bones, teeth and muscle function, and to the normal absorption of calcium and phosphorus. Those are the effects European food law allows us to state, and we keep to them. You will find the wider range in our vitamins collection.

D3, D2 and why the carrier oil matters

D2 (ergocalciferol) comes from yeast and mushrooms. D3 comes from lanolin in sheep's wool or from lichen, a plant-like organism grown for vegan products. Research shows D3 raises vitamin D levels in the blood more reliably than D2, so D3 is what we stock as standard.

The second thing we check is what the D3 actually sits in:

• Softgels and capsules with oil: olive, sunflower or MCT oil, so you do not have to plan a fatty meal around them.
• Drops and oral sprays: easy to dose in small steps, practical for children and for anyone who dislikes swallowing capsules.
• Dry tablets and gummies: convenient, but take them with a meal that contains some fat.

Labels use both micrograms and international units, which causes a lot of confusion. 10 mcg is 400 IU, 25 mcg is 1,000 IU and 100 mcg is 4,000 IU. Doing that conversion is the quickest way to see whether a product marked high strength is really stronger than the one you already have at home.

How we choose vitamin D3

We look at three things: the form, the dose and the combinations. We stock cholecalciferol rather than D2, and we prefer products where the D3 is suspended in oil, because absorption is better that way. We carry 400 IU for a simple daily top-up and higher strengths up to 4,000 IU for people who get very little sun. Vegan D3 from lichen sits next to lanolin-based D3, so the choice stays yours. Every product passes our compliance team, we test products ourselves, and independent labs spot-check batches. You can read how we select brands and products.

Who this collection suits

Most people here are building a winter routine, roughly October to March. Others take D3 all year: if you spend your days indoors, cover your skin, or have darker skin, your body makes less vitamin D from sunlight. Babies and young children have their own drops in lower strengths. A blood test is the only way to know your own level, so without one it makes sense to stay inside the range public health advice sets.

Combination products are popular, and one deserves a word of caution. Formulas that pair D3 with vitamin K2 as MK-7 are not suitable for everyone: if you take warfarin or another vitamin K antagonist, speak to your GP or anticoagulation clinic before you start.

Many people also keep D3 next to a magnesium supplement in the same daily routine. Be realistic about the timeline: vitamin D builds up gradually in the blood, so think in terms of several weeks of consistent daily use, which is exactly why a dose you can keep up beats a dose you forget.