OVERVIEW
Vitamin K is a fat-soluble vitamin that exists in two main forms:
- K1: phytonadione or phylloquinone (dark green leafies)
- K2: menaquinone (made by gut bacteria); there are several varieties of Vitamin K2, including menaquinone-4 (MK-4) and menaquinone-7 (MK-7).
FUNCTIONS
Important functions of vitamin K include:
- Essential for proper blood clot formation (to prevent abnormal bleeding)
- Help to fix calcium in bone (to reduce osteoporosis)
- Reduces acumulation of calcium in arteries (reduces "hardening of the arteries")
- Reduces accumulation of calcium oxalate stones in the kidneys.
SYMPTOMS OF DEFICIENCY
Deficiency symptoms include:
- Abnormal bleeding
- Increased risk of osteoporosis, arterial calcification, and kidney stones.
- Elevated INR or prothrombin time.
SYMPTOMS OF EXCESSS
According to Dr. Gaby, "MK-4 at a dosage of 45 mg/day has not caused serious adverse effects ... in studies of patients ... lasting up to 8 years"
Dosage:
- Recommended Dietary Allowance (Adults): Adequate Daily Intake of Vitamin K is 120mcg/day (adult males); 90mcg/day (adult females)
- Optimum Dose (Adults): [Gaby2011, pg 126] suggests that bone health may benefit from up to 1,000mcg/day
DETAILS
Vitamin K interacts with the drug Warfarin, so when Warfarin is being prescribed to reduce the risk of unwanted blood clot formation (e.g. with heart arrythmias), the dose of Warfarin may need to be increased when Vitamin K supplements or green leafy vegetable consumption is increased. However, Dr. Gaby states that "Vitamin K supplementation probably improves anticoagulant control by decreasing the relative change in total vitamin K intake associated with variations in dietary vitamin K" [Gaby2011, pg 127]. Of course this assumes consistent supplementation dosing and titrating Warfarin dose to the appropriate INR. Patients are advised to discuss this with their health care provider and to not "self-dose" when taking Warfarin.
GENETICS
Absorption of Vitamin K is affected by genetic factors.
SOURCES
The primary source of Vitamin K1 is dark grean leafy vegetables (e.g. turnip greens and crucifferous vegetables); Vitamin K2 is produced by bacteria in the large intestine. Both are fat-soluble, which means that proper absorption requires consumption with a fatty meal, proper bile production by the liver, and a healthy gut. Diseases like celiac and bowel inflammation reduce absorption.
It is notable that salads made with dark green leafies are often mixed with "oil and vinegar" salad dressing. The oil helps with absorption of fat-soluble vitamins like Vitamin K. [The vinegar helps with absorption of minerals]. It has also been shown that buttered cooked spinach gives better absorption of Vitamin K1 than unbuttered cooked spinach.
Other sources of Vitamin K include liver (which stores Vitamin K) and some fermented foods (e.g. nato) [Gaby2011, pg 128]. Vegetable oils contain some vitamin K, but hydrogenation of the oil destroys the Vitamin K.
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