Vitamin K has long been known to be critical to blood clotting. More recent studies show that higher intakes may increase bone mineral density and reduce hip fracture when used in combination with adequate intake of calcium and vitamin D. Studies also suggest that certain forms of vitamin K may reduce the risk of death from heart attack and cancer.
So what's the best vitamin K supplement? Our tests found several products to be of high quality, although one combination product contained much more vitamin D than it claimed -- 182% of the listed amount. We carefully checked products for amounts of K1 and K2 because K2 (in the MK-7 form) can be much more potent and typically costs more. All products were also checked for contamination with lead, and tablets were tested to be sure they would properly break apart in your body. Prices were also compared, showing that you can get 50 mcg of vitamin K for as little as 1 cent from one of the high-quality supplements.
You must join to get the full test results and quality ratings for eight supplements with vitamin K -- three selected for testing by ConsumerLab.com and five others that passed CL's Voluntary Certification Program testing. You'll also get information about one supplement that is the same as one that passed testing but is sold under a different brand name.
In this comprehensive report, you'll discover:
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- Which vitamin K supplements failed our quality ratings and which passed -- including vitamin K-only supplements and combinations including vitamin D and calcium
- Cost comparisons to help you choose a vitamin K supplement offering the best value
- The differences in potency among vitamin K1 and the two forms of vitamin K2 now sold -- menaquinone-4 (MK-4) and menaquinone-7 (MK-7)
- Dosage of vitamin K for specific uses
- Foods containing vitamin K
- Potential drug interactions and side effects of vitamin K, including concerns about soy allergy