Vitamin D3 + K2 in a UK Winter: What to Know

In the UK, the NHS advises that everyone should consider taking 10 micrograms (400 IU) of vitamin D a day between October and March, because winter sunlight is too weak for our skin to make enough. Vitamin D3 with K2 combines that with vitamin K, which contributes to the maintenance of normal bones. This guide explains how much you need, the difference between D3 and D2 and between K2 types, and who needs to take extra care.

NHS vitamin D advice in a UK winter

The NHS explains that between October and early March we do not make enough vitamin D from sunlight, so everyone, including pregnant and breastfeeding women, should consider a daily 10 microgram supplement during these months. Some people are advised to take it all year round, including those who are rarely outdoors, who usually wear clothes that cover most of their skin when outside, or who have dark skin (for example, people with African, African-Caribbean or South Asian heritage).

Key numbers from the NHS:

• Adults and children from age 1: 10 micrograms (400 IU) a day.
• Babies up to 1 year: 8.5 to 10 micrograms a day (formula-fed babies drinking 500 ml or more of formula a day do not need extra).
• Upper limit for adults (including pregnant and breastfeeding women and older people) and children aged 11 to 17: do not take more than 100 micrograms (4,000 IU) a day, as it could be harmful.
• Children aged 1 to 10: no more than 50 micrograms (2,000 IU) a day. Infants under 12 months: no more than 25 micrograms (1,000 IU) a day.

The 10 microgram figure comes from the UK Scientific Advisory Committee on Nutrition (SACN), whose 2016 report set it as the reference intake for most of the population.

Vitamin D contributes to the maintenance of normal bones, to normal absorption and use of calcium and phosphorus, and to the normal function of the immune system.

Micrograms and IU: converting labels

Labels use two units, which causes a lot of confusion. The conversion for vitamin D is simple: 1 microgram = 40 IU.

Micrograms (mcg)	International Units (IU)	What it means
10 mcg	400 IU	NHS daily amount for adults and children over 1
25 mcg	1,000 IU	A common supplement strength; within the adult limit
50 mcg	2,000 IU	Maximum for children aged 1 to 10
100 mcg	4,000 IU	NHS maximum daily amount for adults
1,500 mcg	60,000 IU	High-dose product used under medical supervision

Many Indian brands sell products at different strengths from typical UK ones, so always check the vitamin D figure per tablet and per daily serving, and add up any other products (multivitamins, fortified drinks) you take.

A note on 60,000 IU products

In India, vitamin D3 is widely sold as 60,000 IU capsules or sachets. These are usually prescribed as a weekly or monthly dose by a doctor, often after a blood test. A single 60,000 IU dose is fifteen times the NHS daily upper limit, so these products are intended for use under medical supervision rather than as an everyday supplement. If a clinician has not recommended a high dose for you, stick to products that keep your total daily intake within the NHS limits.

D3 vs D2, and lichen vs lanolin

Vitamin D comes in two main forms:

• Vitamin D3 (cholecalciferol) is the form your skin makes in sunlight. A 2012 systematic review and meta-analysis in the American Journal of Clinical Nutrition found D3 was more effective than D2 at raising blood levels of vitamin D, which is why most supplements now use D3.
• Vitamin D2 (ergocalciferol) comes from plants and fungi, such as UV-exposed mushrooms. It is always vegan.

D3 itself has two common sources:

• Lanolin, a grease from sheep’s wool. It is not vegan, though it is generally acceptable for vegetarians.
• Lichen, a plant-like organism that provides a vegan D3.

If the source matters to you, look for wording such as “vegan D3 from lichen”. If the label does not say, assume it is lanolin-derived and contact the brand to confirm.

Why add vitamin K2?

Vitamin K contributes to the maintenance of normal bones and to normal blood clotting. Pairing it with vitamin D is popular because both play roles in bone health. The NHS says adults need around 1 microgram of vitamin K a day for each kilogram of body weight, and most people get enough from a varied diet that includes green leafy vegetables, vegetable oils and cereals. The NHS adds that taking 1 mg (1,000 micrograms) or less of vitamin K supplements a day is unlikely to cause harm.

Vitamin K comes as K1 (phylloquinone, from plants) and K2 (menaquinones). The two K2 forms you will see on labels are:

• MK-7 (menaquinone-7): found in fermented foods such as natto and usually made by fermentation for supplements. According to the US NIH Office of Dietary Supplements, it has a longer half-life than other forms, so it stays in the body longer. Supplements generally use microgram amounts.
• MK-4 (menaquinone-4): found in some animal foods. It has a shorter half-life, which is why products using it tend to contain larger amounts.

Most D3 + K2 combinations, such as Carbamide Forte Vitamin D3 + K2 (MK-7), use MK-7. If you only want K2, a standalone option such as Health Veda Vitamin K2 lets you take it separately from your vitamin D.

Warfarin and vitamin K: an important caution

If you take warfarin or another vitamin K antagonist anticoagulant, do not start a vitamin K or D3 + K2 supplement without speaking to your anticoagulation clinic, GP or pharmacist. The NIH Office of Dietary Supplements describes the interaction between vitamin K and warfarin as serious and potentially dangerous. People on warfarin need a consistent vitamin K intake, because sudden changes can affect how well the medicine works. Changes to your INR may need monitoring.

Other anticoagulants work differently, but you should still check with a pharmacist before adding any supplement while on blood-thinning medicine.

Calcium, magnesium and combination products

Many D3 + K2 products also contain calcium, and some add magnesium. Calcium is needed for the maintenance of normal bones, and magnesium contributes to the maintenance of normal bones and to a reduction of tiredness and fatigue. Examples include Zanskar Calcium + D3 + K2, Pure Nutrition Calcium Citrate + D3 + K2 and ZeroHarm Calcium + D3 + K2 + Magnesium. If you do not need K2, Neuherbs True Calcium with D3 and Magnesium is another format.

Points to consider with calcium combinations:

• Total calcium: the NHS says adults need 700 mg of calcium a day, and that taking 1,500 mg or less a day from supplements is unlikely to cause harm. Many people already get a good amount from dairy, fortified plant milks, tofu and leafy greens.
• Calcium citrate vs carbonate: calcium carbonate contains more calcium by weight but is generally best absorbed with food; citrate is often chosen by people who prefer to take a supplement without food. Check the label for “elemental calcium”.
• Timing with medicines: calcium can reduce the absorption of some medicines, including levothyroxine and certain antibiotics. A pharmacist can advise how far apart to take them.

Who should check with a GP or pharmacist first

• Anyone taking warfarin or other anticoagulants (because of vitamin K).
• People with kidney problems, or anyone who has been told their blood calcium is high.
• People taking medicines that interact with calcium or vitamin D, such as some heart medicines, thiazide diuretics, levothyroxine or certain antibiotics.
• Anyone who has been prescribed vitamin D by a doctor, so you do not double up.
• Parents choosing a product for a child: use one made for children’s amounts.

Vitamin D is just one part of a winter routine. For warming meals, spices and daily habits, see our Ayurvedic winter warm-up plan, and if you are over 50, our Ayurvedic daily routine for over-50s. You can see the full range in our immunity and wellness category.

Sources and further reading

• NHS, “Vitamin D” – nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
• NHS, “Vitamin K” and “Calcium” – nhs.uk/conditions/vitamins-and-minerals/
• Scientific Advisory Committee on Nutrition (SACN), “Vitamin D and Health” report, 2016 – gov.uk
• NIH Office of Dietary Supplements, “Vitamin K: Fact Sheet for Health Professionals” – ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
• Tripkovic L et al. “Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis.” American Journal of Clinical Nutrition, 2012 – ncbi.nlm.nih.gov/pmc/articles/PMC3349454/

Frequently asked questions

How much vitamin D should I take in a UK winter?

The NHS advises that adults and children over 1 should consider taking 10 micrograms (400 IU) of vitamin D a day between October and March. Adults should not take more than 100 micrograms (4,000 IU) a day.

Is D3 better than D2?

A 2012 systematic review found vitamin D3 was more effective than D2 at raising blood levels of vitamin D, which is why most supplements use D3. Vitamin D2 is always vegan, while D3 can be vegan if it comes from lichen.

Should I choose MK-7 or MK-4 vitamin K2?

Most D3 and K2 combinations use MK-7, which stays in the body longer and is used in microgram amounts. MK-4 has a shorter half-life and is used in larger amounts. Both are forms of vitamin K, which contributes to the maintenance of normal bones.

Can I take vitamin D3 and K2 if I am on warfarin?

Do not start a vitamin K supplement without speaking to your anticoagulation clinic, GP or pharmacist. Vitamin K can affect how warfarin works, and people on warfarin need a consistent vitamin K intake.

Are 60,000 IU vitamin D3 capsules safe to take?

A 60,000 IU dose is fifteen times the NHS daily upper limit for adults. These high-dose products are intended for use under medical supervision, so only take them if a doctor has recommended them for you.

This guide is for general information and is not medical advice. Food supplements should not replace a varied, balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking medication or under medical supervision, speak to a healthcare professional before using herbal supplements.