Vitamin D3 + K2 (MK-7): What They Are, Why They Are Paired and How to Choose
Vitamin D3 and vitamin K2 are often sold together, and more and more products also add calcium. But what is the difference between D2 and D3, what does "MK-7" mean, and why is black pepper extract in a vitamin capsule? This guide explains each ingredient in plain English and shows what to check on the label.
Vitamin D3: The "Sunshine Vitamin"
Vitamin D is unusual: your body can make it itself when your skin is exposed to sunlight (UVB rays). That is why it is often called the sunshine vitamin. How much your skin produces depends on the season, where you live, the time you spend outdoors, your skin tone and how much skin is covered. In winter, at northern latitudes or with mostly indoor work, many people make very little.
Only a few foods contain meaningful amounts of vitamin D, mainly fatty fish, egg yolks and fortified foods like milk or cereal. Vitamin D contributes to the normal absorption and use of calcium in the body.
D2 or D3?
- Vitamin D2 (ergocalciferol) comes from plants and fungi.
- Vitamin D3 (cholecalciferol) is the form your own skin makes and the form found in animal foods.
Most quality supplements today use D3.
Micrograms and IU
Labels show vitamin D in two units. Here is the simple conversion: 1 mcg = 40 IU. So 125 mcg equals 5,000 IU, and 25 mcg equals 1,000 IU. Higher-dose products like 5,000 IU are common, but the right amount depends on the person. Many people ask their doctor to check their vitamin D level with a simple blood test before choosing a dose.
Vitamin K2: Not the Same as K1
When people hear "vitamin K", they often think of leafy greens. That is vitamin K1. Vitamin K2 is a different group of compounds called menaquinones, found mainly in fermented foods and some animal products. The best-known food source is natto, a traditional Japanese dish made from fermented soybeans.
What Does MK-7 Mean?
Vitamin K2 comes in several forms, named MK-4 to MK-13. The two you see most often on labels:
- MK-4 stays in the body only for a short time.
- MK-7 stays in the body much longer, which is why many supplements use it for once-daily dosing.
Vitamin K contributes to normal blood clotting and to the maintenance of normal bones. That is also why it matters for people on certain medications (see below).
Why D3 and K2 Together?
Vitamin D supports calcium absorption from food. Vitamin K2 is needed to activate proteins that help the body use calcium. Because the two vitamins work in the same area, many people prefer to take them together in one product instead of buying two separate bottles.
Why Calcium in the Same Capsule?
Some formulas add a moderate amount of calcium, for example around 200 mg, to round out the trio. This is not meant to cover your full daily calcium need, which mostly comes from food like dairy, leafy greens, almonds or fortified drinks. It simply adds a small amount alongside D3 and K2.
And the Black Pepper Extract?
BioPerine® is a patented extract from black pepper fruit, standardized to piperine, the compound that gives pepper its sharpness. It is added to many supplements in small amounts, usually around 5 mg, because it is known to support the absorption of nutrients.
Take It With a Meal
Vitamins D and K are both fat-soluble. They dissolve in fat, not in water. That is why the best time to take them is with a meal that contains some fat, such as breakfast with eggs or yogurt, or dinner.
Important: Blood Thinners
Because vitamin K plays a role in normal blood clotting, it can interfere with blood-thinning medication such as warfarin. If you take any blood thinner or other medication, talk to your doctor before starting a product with vitamin K2. This is not optional.
Checklist Before You Buy
- Is it D3 (cholecalciferol), not D2?
- Is the dose shown in mcg and IU, and does it fit you?
- Is the K2 form named, ideally MK-7?
- Is the capsule vegetarian, if that matters to you?
- Is it one capsule a day, or several?
- Is it made in a GMP or NSF-registered facility?
Our Formula
SUPPLI-X D3 + K2 Complex combines vitamin D3 125 mcg (5,000 IU), vitamin K2 as MK-7 100 mcg, calcium 210 mg and BioPerine® 5 mg in one vegetarian capsule. One capsule a day with a meal, 60 capsules per bottle, gluten-free and lactose-free, made in the USA in an NSF-registered facility.
FAQ
What is the difference between vitamin D2 and D3?
D2 (ergocalciferol) comes from plants and fungi. D3 (cholecalciferol) is the form your skin makes in sunlight and the form most quality supplements use.
How do I convert vitamin D from mcg to IU?
1 mcg equals 40 IU, so 125 mcg is 5,000 IU.
What does MK-7 mean on a vitamin K2 label?
MK-7 is a form of vitamin K2 that stays in the body much longer than MK-4, which is why it is used for once-daily dosing.
Can I take vitamin K2 with blood thinners?
Talk to your doctor before starting vitamin K2 if you take any blood thinner, such as warfarin.
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. If you are pregnant, nursing, taking medication or have a medical condition, talk to your healthcare provider before using any supplement.
