Vitamin D3 + K2 Drops: What I Wanted to Know About Dosage and the Combination

Last Sunday the clocks went back, and since then my evenings have felt like midnight. I leave the office: dark. I come out of the gym: dark. My body is rightly wondering where the sun went – and I'm wondering whether I should be taking vitamin D now.

Welcome to part 2 of Selina's Sport Edit. Last week we packed the gym bag; today we're heading to the supplement shelf. And because I work with numbers for a living, I'm doing it the way I read any statistic: facts first, headline second. If you want to go deeper into deficiency, symptoms and blood levels, you'll find that in Vitamin D: recognising deficiency and supplementing correctly.

Why vitamin D becomes a topic in winter

The body produces most of its vitamin D itself – with the help of UVB radiation on the skin. In Germany and Austria the sun is so low from about October to March that production hardly works any more. We only get a little from food; significant amounts are found mainly in oily fish.

Vitamin D contributes to the normal function of the immune system, the maintenance of normal bones and normal muscle function. Especially if you work indoors a lot, work shifts or rarely get into the sun in winter, your levels can be too low during the dark months. Honestly, I count myself among the "office-light houseplants".

What vitamin K2 contributes

Vitamin K comes in two main forms: K1 is found mainly in green leafy vegetables, K2 (menaquinones) in fermented foods and animal products. Vitamin K contributes to normal blood clotting and the maintenance of normal bones.

The idea behind the combination: vitamin D ensures calcium is absorbed, vitamin K is involved in proteins that bind calcium in bone. So the two complement each other. To be honest, though, it hasn't been proven that healthy people strictly need K2 with usual amounts of vitamin D – the combination makes sense, but it's not a must. That's the difference between "sounds logical" and "is proven", and I pay attention to it.

Drops, tablets or capsules?

Vitamins D and K are fat-soluble. In drops they are dissolved in oil, usually medium-chain triglycerides (MCT) from coconut oil. This has advantages:

Precise dosing: One drop is one dose – practical for anyone who doesn't like swallowing tablets.

Taken with fat: The oil helps absorption. Still, it's best to take the drops with a meal. Mine lands on a spoon next to my porridge in the morning.

Long-lasting: A small bottle lasts a very long time.

The downside: if you're not careful, you can quickly get two or three drops instead of one. So be patient for a second, hold the bottle upright and drop it onto a spoon or directly onto your food – not on the side while making coffee.

Maximum amounts: what the BfR and EFSA say

With vitamin D, more is not better. Too much over a long period can raise calcium levels and strain the kidneys and blood vessels.

The BfR derives its proposal from the EFSA upper limit with a safety margin, so that people who use several fortified products also stay within the safe range. The proposal is a recommendation, not a law. For me as a numbers person, the most important line: if you combine a multivitamin, fortified foods and a vitamin D supplement, add up the amounts once.

Practical example: the Syrax Vitamin D3 + K2 drops

According to the product specification, our drops are based on MCT oil from coconut with cholecalciferol (vitamin D3) and menaquinone-7 (vitamin K2). One drop provides:

At 25 µg, the daily dose is slightly above the BfR proposal of 20 µg and well below the EFSA upper limit of 100 µg. In practice that means: one drop a day, no more, and no other vitamin D supplements on top. The K2 content is below the BfR proposal of 25 µg. The drops are taste-neutral, contain no added sugar and are analysed for heavy metals and microbiology.

Who vitamin D3 + K2 can make sense for

• people who get hardly any daylight in winter, for example in the office or working shifts,
• older people, whose skin produces less vitamin D,
• people with darker skin living in northern latitudes,
• anyone whose blood test has shown a low level.

People who should not take vitamin D without medical advice: those with kidney disease, high calcium levels or sarcoidosis, as well as pregnant and breastfeeding women who have already been prescribed supplements. Children need their own, lower doses.

Light is still your best friend

As practical as drops are, they don't replace a lunchtime walk in the fresh air. In winter I try to put at least some of my exercise into daylight – a walk in my lunch break, padel on Saturday morning, a run on Sunday. It's good for my mood and my sleep-wake rhythm, and on sunny days it's at least a small contribution. I'll tell you how to dress for it next week.

Storage and shelf life

Vitamins D and K are sensitive to light and heat. Keep the drops tightly closed, cool, dry and protected from light – so not on a sunny windowsill but in a cupboard. With our drops, the best-before date and batch number are on the bottom of the bottle.

Conclusion: simple, but not arbitrary

Vitamin D3 + K2 drops are an easy way to get through the dark months well. What matters is the right dose: one drop a day, no doubling up with other supplements, and talk to your doctor first if you take medication or have pre-existing conditions. Then the combination is a sensible addition – not a substitute for exercise in the fresh air.

Next Friday in part 3: Training outdoors in winter – the layering principle, the hat question and why cotton is a bad idea in the cold.