Vitamin D Supplements

Choosing a vitamin D supplement

The body makes most of its vitamin D from sunlight on your skin. In the UK the sun is too weak for the body to produce significant quantities of vitamin D from October to early March. Very few foods contain it naturally, which is why so many people take additional vitamin D through autumn and winter.

Some people produce less vitamin D than others all year round. This applies to people with darker skin, people who spend little time outdoors and people who keep most of their skin covered when they are outside. The skin also produces less vitamin D as we get older.

Vitamin D contributes to the maintenance of normal bones, teeth and muscle function. It also contributes to the normal function of the immune system and to the normal absorption of calcium.

The amount of vitamin D in a supplement is measured in international units, shown on the label as IU. One microgram of vitamin D is equal to 40 IU. Each of our capsules provides 2,500 IU, which is a higher amount that people often choose after a blood test has shown their vitamin D level is low. Our oils are measured in drops, which makes it easy to take a smaller amount. Four drops of the D3 oil provide 500 IU, while ten drops of the D3 with K2 oil provide 1,000 IU. Vitamin D is fat soluble, so take it with food.

Vitamin D3 with K2

Vitamin D helps the body absorb calcium from food. Vitamin K activates osteocalcin, which is the protein that binds calcium into bone. This is why vitamin D3 and vitamin K2 are so often taken together. Vitamin K contributes to the maintenance of normal bones and to normal blood clotting.

Each capsule provides 2,500 IU of vitamin D3 and 200 mcg of vitamin K2 in the MK-7 form. The directions are to take one capsule a day with food. The oil provides 1,000 IU of vitamin D3 and 50 mcg of vitamin K2 in every ten drops. It is often chosen by people who prefer drops to capsules, or who want a lower daily amount than the capsule provides. Vitamin K2 is also available on its own on the vitamin K2 page.

Vegan vitamin D3

Most vitamin D3 supplements are made from lanolin, which is the oil in sheep's wool, so they are not suitable for vegans. The vitamin D3 in this capsule is made from algae instead. It is still vitamin D3, which is the same form your body makes from sunlight. Vitamin D3 may raise the level of vitamin D in the blood higher and for longer than vitamin D2, the form that comes from plants and mushrooms.

Each capsule provides 2,500 IU of vitamin D3 and 200 mcg of vitamin K2. The directions are to take one capsule a day with food.

Vitamin D3 oil drops

These drops contain vitamin D3 dissolved in avocado oil, with nothing else added. Four drops provide 500 IU of vitamin D3. The amount you take depends on the number of drops, so one bottle can be used by both adults and children. The directions for adults are 20 drops a day, which provides 2,500 IU. Children under 13 take 4 to 8 drops a day, while those aged 13 to 18 take 12 to 16 drops a day. The drops are available in 100 ml, 250 ml and 500 ml bottles.

We recommend speaking to a GP or pharmacist first if you are pregnant, planning a pregnancy or taking anything on prescription, including medicine that affects blood clotting.

Not sure which one fits? Ask Nutri365, the Nutri Tailor AI health expert. Nutri365 checks for interactions and contraindications.

Written by Nutri Tailor from the Health Reference Library. Last checked 6 October 2026. General information, not personal advice.