Vitamin K may not be as popular and well known as other vitamins and if known at all, it’s for the important role it plays in blood clotting. However, vitamin K is also essential to building strong bones and preventing heart disease.
There are two natural forms of vitamin K. Vitamin K1 (also called phylloquinone) is plentiful in leafy green vegetables, such as kale, collards, spinach and mustard greens, so it’s easy to obtain this vitamin when following a nutritious diet.
Vitamin K2 (a few different substances called menaquinones), is produced by microorganisms and scarce in plant foods, so K2 is more difficult to get from a Nutritious diet. The human body can synthesize some K2 from K1, and intestinal bacteria can produce some K2, but these are very small amounts.5
There is evidence that both vitamin K1 and K2 are important for good health.
Vitamin K is important for:
- Blood coagulation
- Essential for the process of blood clotting. In fact, vitamin K was named for this important function; the scientists who discovered the vitamin named it using the first letter of the German word "koagulation."
- Bone health and fracture prevention
- Vitamin K allows the body to utilize the calcium needed for bone and tooth formation.1,2 Many studies have associated low vitamin K1 or K2 status with a higher risk of hip fracture or low bone mineral density.2-4
- Higher intake of vitamin K1 is associated with lower rates of bone loss and fractures, and studies have reported that a causative factor of the low hip fracture incidence in Japan was natto, a fermented soy food, rich in K2. Following this observation, several studies found supplementation with vitamin K2 to be particularly effective at improving bone health. A review of randomized controlled trials found that vitamin K2 reduced bone loss and reduced the risk of fractures; vertebral fracture by 60 percent, hip fracture by 77 percent and all non-vertebral fractures by 81 percent.3,6
- In a more recent study on postmenopausal women taking vitamin K2 supplements daily for three years, decreases in bone loss and bone mineral decline, and increased bone strength were found in the vitamin K2 group compared to placebo.7
- In women who already had osteoporosis, Vitamin K2 supplementation was also shown to reduce the risk of fracture, reduce bone loss, and increase bone mineral density.8
- Heart health via interactions with calcium
- Vitamin K helps prevent calcification of the coronary arteries (arteries that give blood to the heart). A vitamin K-dependent protein binds up calcium to protect the soft tissues – including the arteries – from calcification.2,9,10 Vitamin K2 in particular, helps to prevent the artery wall from stiffening and maintaining elasticity. Coronary artery calcification is a predictor of cardiovascular events, as is arterial stiffness.11,12
- Higher vitamin K2 intake has been linked with a lower likelihood of coronary calcification (the same association was not found for K1).10 In 2004, the Rotterdam Study revealed that increased dietary intake specifically of vitamin K2 significantly reduced the risk of coronary heart disease by 50 percent as compared to low dietary vitamin K2 intake. In this study, Vitamin K1 had no effect.9
- Similar results were found in another study conducted in 2009.13 Furthermore, a systematic review of several studies in 2010 also found no association between vitamin K1 intake and coronary heart disease, but higher K2 intake was associated with lower risk.14
It is unclear why vitamin K2 seems to be more beneficial than K1 for the cardiovascular system; it could be due to differences in absorption or biological activity between the vitamin K forms.2,15 Regardless of the reason, the evidence suggests that taking in vitamin K2 in addition to K1 is likely beneficial to help protect against vascular calcification.
Leafy greens for K1, supplements for K2
Ongoing research on vitamin K is revealing new ways that vitamin K acts to maintain good health. There is some evidence that vitamin K is involved in insulin metabolism, and higher intake of vitamins K1 and K2 are associated with lower risk of type 2 diabetes.16,17
Future studies will also help us to understand why K2 appears more protective against blood vessel calcification, and whether there are benefits of vitamin K that are exclusive to either K1 or K2. Leafy green vegetables provide generous amounts of vitamin K1, and getting K2 from a supplement is likely beneficial.