AG1 Vitamin D3 K2

What it is

AG1’s Vitamin D3 + K2 is a liquid dropper. A two-drop serving delivers 1,000 IU of vitamin D3 and 100 mcg of vitamin K2, split evenly between the MK-4 and MK-7 forms. The label directs two to four drops daily, so the dose is meant to be adjusted rather than fixed. An oil-based liquid is a sensible vehicle for a fat-soluble vitamin, and the dropper makes small dose changes possible in a way a hard 5,000 IU capsule does not.

Why it’s on this list

Insufficient vitamin D is genuinely common — among people who work indoors, live at northern latitudes, or have darker skin. Correcting a real deficiency is a legitimate reason to take a supplement, and vitamin D’s role in bone and calcium metabolism is not in dispute. The K2 is included on the theory that it directs calcium toward bone rather than arterial walls. Biologically plausible — but the human outcome evidence behind it is thinner than the supplement aisle implies, and it should be labeled a theory.

Now the part that keeps this page honest. VITAL, the largest randomized trial of the question — nearly 26,000 American adults taking 2,000 IU a day for around five years — found no reduction in invasive cancer or major cardiovascular events in a population that was, on average, not deficient to begin with. Vitamin D is not a life-extension pill. It is a nutrient you should not be short of. Those are different products, and only one of them is real.

The case for drops over a capsule is control: 1,000 IU or 2,000 IU depending on the season and your blood work, instead of whatever dose a factory settled on.

What to know before you buy

• Test, don’t guess. A 25-hydroxyvitamin D blood test is inexpensive and turns this into a decision. Supplementing blind is how people end up taking something they don’t need, or too little of something they do.
• Vitamin K interacts with warfarin. If you take an anticoagulant, do not start a K2 product without speaking to the doctor who manages it. This is not a formality.
• D3 is a commodity. Plain drugstore D3 costs a fraction of this. Here you pay for the brand, the K2 and the dropper. For many readers the generic bottle is the better buy, and we would rather say so.
• More is not better. Vitamin D is fat-soluble and accumulates. Stay within the label unless a doctor says otherwise.
• Talk to a doctor before starting any supplement — especially this one if you take medication or have a kidney or parathyroid condition. Sunlight and oily fish remain the baseline this is meant to top up.