“Everyone taking vitamin D also needs vitamin K2.”
People who take vitamin D do not need to add vitamin K2 to stay safe.
Vitamin D at 2,000 IU a day was not shown to be risky without K2. Adding K2 is a personal choice, not a requirement.
If you take vitamin D, you can keep taking it without adding K2. If you take warfarin, check vitamin D labels for K2 before you buy.
Safety note: Vitamin K2 can weaken warfarin and similar blood thinners that work against vitamin K. In a study of healthy volunteers taking one of these drugs, as little as 10 micrograms a day of K2 (MK-7), less than the usual 45 microgram retail dose, lowered blood-thinning levels enough to matter in some people. The researchers said people on these drugs should avoid MK-7 supplements. Some vitamin D products include K2, so check the label.
Talk to a healthcare professional if: you take warfarin or another blood thinner that works against vitamin K and are thinking of starting or stopping K2 or a vitamin D product that contains it.
A five-year trial of more than 25,000 adults taking vitamin D without K2 found no rise in heart attacks, strokes or high blood calcium, and trials adding K2 have not shown the combination is needed. Confidence is moderate because no large trial has compared vitamin D alone with vitamin D plus K2 head to head.
People who take vitamin D do not need to add vitamin K2 to stay safe. In a large five-year trial, adults taking 2,000 IU of vitamin D a day without K2 had no more heart attacks, strokes or cases of high blood calcium than those taking a placebo. A two-year trial of K2 plus vitamin D did not show a clear benefit for artery calcium.
The VITAL trial randomly assigned 25,871 U.S. adults (men 50 and older, women 55 and older) to 2,000 IU of vitamin D a day or placebo for a median of 5.3 years. Heart attacks, strokes and deaths from heart disease were about the same in both groups, and the trial found no excess high blood calcium. A Danish trial gave 389 older men K2 (720 micrograms) plus vitamin D (25 micrograms, or 1,000 IU) or placebo for two years. In 304 men without known heart disease, coronary artery calcium rose in both groups, with no clear difference (203 vs 254 units). Fewer heart attacks, artery-opening procedures and deaths in the supplement group (1.9 percent vs 6.7 percent) were a side finding that the authors said needs testing in new studies. That trial compared the combination with placebo, so it cannot show what K2 adds to vitamin D. Its supplement tablets were donated by K2 and supplement companies.
- Manson JE, Cook NR, Lee IM, et al.; VITAL Research Group. Vitamin D supplements and prevention of cancer and cardiovascular disease. New England Journal of Medicine. 2019;380(1):33-44. DOI: 10.1056/NEJMoa1809944. PMID: 30415629. PMCID: PMC6425757
- Hasific S, Oevrehus KA, Lindholt JS, et al. Effects of vitamin K2 and D supplementation on coronary artery disease in men: a RCT. JACC: Advances. 2023;2(9):100643. DOI: 10.1016/j.jacadv.2023.100643. PMID: 38938724. PMCID: PMC11198368
- Theuwissen E, Teunissen KJ, Spronk HM, et al. Effect of low-dose supplements of menaquinone-7 (vitamin K2) on the stability of oral anticoagulant treatment: dose-response relationship in healthy volunteers. Journal of Thrombosis and Haemostasis. 2013;11(6):1085-1092. DOI: 10.1111/jth.12203. PMID: 23530987