Vitamins and minerals are nothing new to us. We know about vitamin C for colds, B vitamins for energy, vitamin A for eyesight and vitamin D for, well, just about everything.
But what about a lesser-known vitamin? The one that is, in reality, two distinct forms of the same vitamin, yet function so differently in the body? The one that supports both bone and heart health through its interaction with calcium? We are talking about vitamin K.
What is Vitamin K?
Vitamin K is a fat-soluble vitamin that is produced by bacteria in the intestines. There are two natural forms of vitamin K: K1 and K2.
Vitamin K1 is synthesized from plants and is also known as phylloquinone, phytomenadione or phytonadione. (Note the phyllo- and phyto- prefixes, which frequently denote something that is plant-based.) It is found primarily in green leafy vegetables. Animals can convert K1 to K2.
Vitamin K2 is the form most commonly found in animals. Just as vitamin K itself has two natural subtypes, K2 also has several subtypes known as menaquinones.
The best food sources of vitamin K2 are natto (fermented soybeans), goose and chicken liver, soft cheese (i.e. brie) and egg yolk.
Conditions Supported by Vitamin K
What Does the Research Say?
While vitamin K is often studied for both bone and heart health, there is research showing that it may be useful in reducing the risk for type 2 diabetes. Researchers followed 1,069 elderly subjects at high risk of cardiovascular disease for an average 5.5 years. The investigators assessed the subjects annually for biochemical and body markers to assess the development of type 2 diabetes. The subjects completed yearly food frequency questionnaires to determine vitamin K1 intake.
The researchers showed that the subjects who developed type 2 diabetes during the study had lower vitamin K1 intake at the beginning of the study. In fact, the investigators found that risk of incident diabetes was 17 percent lower for each additional intake of 100 mcg vitamin K1 per day.
Furthermore, the subjects who increased their dietary intake of vitamin K1 during the follow-up period had a 51 percent reduced risk of developing diabetes, as compared with subjects who decreased or did not change the amount of vitamin K1 intake.
The researchers stated, “We conclude that dietary [vitamin K1] intake is associated with reduced risk of type 2 diabetes.”
One of the most studied areas of vitamin K lies in bone health. According to a study published in September 2013, Vitamin K helps decrease bone loss in postmenopausal women.
Researchers divided 244 healthy postmenopausal women into two groups. One group received a placebo and the other received 180 mcg of Vitamin K a day for three years. They also tested several bone health markers at the start of the study and again at years one, two and three years.
At the end of the study, researchers found that those women taking the vitamin K enjoyed improved vitamin K status and a decrease in the age-related decline of bone mineral density. They also had improved bone strength. They concluded, “Vitamin K supplements may help postmenopausal women to prevent bone loss.”
Similarly, a study published in May 2014 reviewed eight randomized, placebo-controlled trials that looked at the role of vitamin K2 plays in postmenopausal women with osteoporosis. Researchers found that Vitamin K increased lumbar spine bone mineral density and reduced the incidence of fractures. They concluded,
“This review of the literature revealed positive evidence for the effects of K2 monotherapy on fracture incidence in postmenopausal women with osteoporosis.”
Vitamin K2 in particular has been shown to be beneficial for supporting healthy blood pressure levels. Studies have revealed that increased intake of this important nutrient will keep calcium from building up in your arteries, helping to keep them flexible and unobstructed.
Other research indicates that 45 mcg of K2 taken daily reduces calcification of the arteries. For example, one specific study found that serum vitamin K is associated with coronary artery calcium progression in individuals taking blood-pressure-lowering medications.
With so much attention on vitamin K and bone health, it’s not surprising to see that a study published in March 2013 reported that subclinical vitamin K deficiency is associated with increased risk of developing knee osteoarthritis.
Researchers evaluated 1,180 subjects with an average age of 62 years and average body mass index (BMI) of 30 kg/m2. The subjects underwent knee x-rays and MRIs at the beginning of the study and again after 30 months. The investigators also measured plasma vitamin K1 levels at the beginning of the study.
The researchers found that subclinical vitamin K1 deficiency was associated with a 56 percent increased risk of knee osteoarthritis and 139 percent increased risk of cartilage lesions, compared to the subjects with sufficient vitamin K. The subjects with subclinical vitamin K1 deficiency were also 33 percent more likely to develop osteoarthritis in one or both knees compared to neither knee.
How to Use Vitamin K
Vitamin K is a critical nutrient for a wide range of health issues. Depending on your particular concern, the dosages and form to use can vary.
Note: People taking vitamin K with the blood thinner Coumadin (warfarin) should be very cautious, because it interferes with the drug’s mechanism of action. If you are currently taking Coumadin, consult with your physician before taking vitamin K.