As the days get shorter, most of us spend less time in the sun. That matters for vitamin D, because your body makes it when sunlight hits bare skin. So fall and winter are when a lot of people start asking what D3+K2 is and whether they should take it.
What is D3+K2? It is a supplement that pairs two vitamins in one product. Vitamin D3 is the form of vitamin D your skin makes from sunlight, and vitamin K2 is a form of vitamin K. Both play a part in how your body uses calcium, which is why they are often taken together.
What Each Vitamin Does
According to the NIH, vitamin D helps your body absorb calcium, one of the main building blocks for strong bones. Your muscles need it to move, your nerves need it to carry messages, and your immune system needs it to fight off bacteria and viruses.
Vitamin K is important for blood clotting and healthy bones. On supplement labels, K2 often shows up as MK-7 (menaquinone-7), which is the form in our drops.
Why You May Need D3+K2 in Fall and Winter
Your skin makes vitamin D from sunshine, but the NIH notes that clouds, age and darker skin all cut down how much it makes. Your skin also can't make vitamin D through a window. In fall and winter the days are shorter and colder, and most of us spend more of the day indoors and covered up.
Food doesn't fill the gap easily. Very few foods have much vitamin D naturally. Fatty fish like salmon and trout are some of the best sources, and most of the vitamin D in American diets comes from fortified foods like milk and cereal.
The NIH says almost one in four people in the US have vitamin D levels that are too low for bone and overall health. People more likely to come up short include:
- older adults, since skin makes less vitamin D with age
- people who rarely get sun on their skin
- people with darker skin
- people whose bodies have trouble absorbing fat
A blood test through your doctor is the reliable way to know where your level is.
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How Does D3+K2 Help Build Strong Bones?
Vitamin D helps you absorb calcium, and vitamin K is part of how your body builds healthy bone. That is the main reason people take the two together.
Research on the pair is still early. In one small two-year study of 92 older women with low bone density, the group taking both vitamins had a bigger gain in lower-spine bone density than the groups taking either one alone. That study used a much higher dose of a different form of K2 than most supplements, ours included. A 2021 review of other trials found mixed results, so the combination is still being studied.
How Does D3+K2 Help the Immune System?
Most of the immune support comes from the vitamin D side. The NIH lists the immune system as one of the places your body needs vitamin D, along with your bones, muscles and nerves. Studies haven't yet shown that adding K2 changes what vitamin D does for immunity, so D3 is the immune half of the pair and K2 is mainly there for your bones.
How Much Do You Need?
The NIH recommends 600 IU (15 mcg) of vitamin D a day for adults up to age 70, and 800 IU (20 mcg) after that. The upper limit for adults is 4,000 IU (100 mcg) a day from all sources, unless your doctor recommends more for a while. Too much vitamin D, almost always from supplements, can cause nausea, muscle weakness and kidney stones.
For vitamin K, the NIH recommends 120 mcg a day for adult men and 90 mcg for adult women. Vitamin K can interact with the blood thinner warfarin (Coumadin), so if you take a blood thinner, talk to your doctor before adding K2.
A Simple Way to Add D3+K2 to Your Day
Our Vitamin D3 + K2 is a liquid supplement. One serving is 5 drops, which gives you 4,000 IU of vitamin D3 and 90 mcg of vitamin K2 (MK-7). Because that serving is right at the adult upper limit for vitamin D, don't take it alongside other vitamin D supplements unless your doctor tells you to. A 1 fl oz bottle holds about 600 drops, so it lasts around four months.
Everything we make at 3rd Rock Essentials is food-grade. If you're building a fall routine, our post on how zinc supports the immune system covers the other supplement people reach for this time of year.
FAQ
What is D3+K2?
D3+K2 is a supplement that combines vitamin D3 and vitamin K2. Vitamin D helps your body absorb calcium, and vitamin K is important for healthy bones, so the two are often taken together.
Why do we need D3+K2 in fall and winter?
Your skin makes vitamin D from sunlight. In fall and winter, shorter days and more time indoors mean less sun on your skin, and few foods have much vitamin D, so many people use a supplement during those months.
Is D3+K2 better than vitamin D3 alone?
The research is mixed. One small two-year study found a bigger bone density gain with both vitamins than with either alone, but a 2021 review of other trials found inconsistent results.
How much D3+K2 should I take?
Follow the label on your supplement. The NIH upper limit for vitamin D in adults is 4,000 IU a day from all sources, and you should check with your doctor first if you take a blood thinner or other vitamin D supplements.
Sources
- Vitamin D: Fact Sheet for Consumers, NIH Office of Dietary Supplements. What vitamin D does, sunlight and food sources, who may run low, recommended amounts and upper limit.
- Vitamin K: Fact Sheet for Consumers, NIH Office of Dietary Supplements. What vitamin K does, recommended amounts and the warfarin interaction.
- Vitamin K2 and vitamin D3 combination study, 2001. A randomized two-year study of 92 women, supporting the lower-spine bone density finding.
- Review of vitamin D and vitamin K supplementation, 2021. Supports the statement that trials of the combination reached mixed results.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for education and is not medical advice.
