The clocks go back this weekend, and for many of us that’s the signal that sunshine is about to get scarce. It’s also when vitamin D supplements start flying off the shelves, often alongside vitamin K2. Here’s what you should know before you choose one.
Why autumn and winter matter for vitamin D
NHS guidance says that from roughly late March or early April to the end of September, most people can make the vitamin D they need from sunlight on their skin. For the rest of the year, UK sunlight is too weak. NHS Inform advises everyone over one year old to consider a daily supplement containing 10 micrograms of vitamin D, and some groups should take it all year. Those include people who are rarely outdoors, people who cover most of their skin outside, and people with dark skin. nhsinform
What do vitamin D and vitamin K do?
Vitamin D helps regulate calcium and phosphate in the body. Vitamin K is needed for blood clotting, and there’s also some evidence it may help keep bones healthy, according to the NHS. In Great Britain, the authorised wording is that vitamin D contributes to the normal absorption of calcium and to the maintenance of normal bones, teeth and muscle function. Vitamin K contributes to normal blood clotting and the maintenance of normal bones. nhs.uk
Vitamin K2 (menaquinone) is a form of vitamin K that’s popular in supplements. The idea behind pairing it with D3 is that D3 helps you absorb calcium while K2 activates proteins involved in how calcium is used.
What does the research say about adding K2?
The picture is promising but mixed. A 2026 randomised trial in Frontiers in Nutrition noted that a meta-analysis of eight randomised trials suggested vitamin K combined with D significantly decreased undercarboxylated osteocalcin and increased bone mineral density. However, the new trial itself found that baseline vitamin K status had no influence on how vitamin D supplementation affected bone turnover markers or cardiovascular parameters. frontiersinfrontiersin
A meta-analysis on bone turnover markers in postmenopausal osteoporosis also cites a three-year trial where 375 µg a day of MK-7 improved osteocalcin carboxylation but did not change bone turnover markers or bone density in people already taking calcium and vitamin D. frontiersin
In short, the combination makes biological sense, but trial results vary and no UK body currently recommends routine vitamin K co-supplementation with vitamin D. Whether it’s right for you is worth discussing with a pharmacist or GP.
Who should check first?
This matters, so we’ll be upfront.
The NHS recommendation for most adults is 10 µg (400 IU) a day. The adult upper limit is 100 µg (4,000 IU) a day unless a healthcare professional advises otherwise. The European Food Safety Authority sets its upper limit at 100 micrograms per day, while the UK’s Expert Group on Vitamins and Minerals previously identified 25 micrograms per day as a level not expected to cause adverse effects. NHS 111 Wales also warns that taking too much vitamin D over a long period can cause calcium to build up in the body (hypercalcaemia), and that some medical conditions mean a person can’t safely take as much. food
Our featured product, Applied Nutrition Vitamin D3 & K2, provides 100 µg (4,000 IU) of vitamin D3 per serving. That’s a high-strength product, ten times the standard NHS daily amount and at the top of the adult limit. So:
- Don’t take other vitamin D products alongside it. Remember to count multivitamins and fortified foods too.
- It isn’t suitable for children.
- Speak to your GP or pharmacist first if you’re pregnant or breastfeeding, have a kidney condition or high calcium levels, or take regular medication. A lower-strength vitamin D may suit you better if you only want the standard NHS top-up.
- If you take warfarin, don’t start vitamin K without advice. The NHS advises against taking vitamin K supplements while on warfarin, because vitamin K can affect how the medicine works. Speak to your anticoagulation clinic first. healthspan
Meet the product: Applied Nutrition Vitamin D3 & K2
The Applied Nutrition Vitamin D3 & K2 pack contains 60 capsules for 30 servings, at £14.95. The formula is vegetarian-friendly and Halal certified. Each serving provides 100 µg (4,000 IU) of vitamin D3.
Both vitamins are fat-soluble, so taking them with a meal containing some fat improves absorption. supp
You can browse the rest of our range in all products, or contact our team on 0800 138 3847 if you’d like help choosing.
Frequently asked questions
How much vitamin D should I take in winter?
The NHS advises 10 µg (400 IU) a day for most adults and children over one, particularly from October to March.
Is 4,000 IU of vitamin D too much?
It’s the upper limit for adults, so it’s best taken knowingly, for example on the advice of a healthcare professional. Never exceed it.
Do I need K2 with vitamin D3?
No UK body currently recommends routine K2 co-supplementation. The NHS says most people can get the vitamin K they need from a varied diet.
Can I take vitamin D3 and K2 together?
Many people do, but avoid vitamin K supplements if you take warfarin unless advised.
When should I take it?
With a meal that contains some fat.
The bottom line
Vitamin D matters most in the darker months, and the NHS standard is a modest 10 µg a day. K2 is an interesting partner, but the evidence for adding it is still developing. If you choose a high-strength product like ours, take it deliberately, check with a professional first if any of the cautions above apply to you, and don’t exceed the label.
Food supplements should not replace a varied, balanced diet. Do not exceed the recommended daily intake. Not suitable for children.