Natural foods provide two basic forms of vitamin K: K-1, or phylloquinone, and K-2, or menaquinone. Menaquinone occurs in in at least 7 different variations, each referred to as MK-n. For example, MK-4 occurs naturally in meat and eggs. Colonic bacteria produce the variations MK-6 to MK-11, with MK-10 predominating (1).
Colonic bacteria produce only very small amounts of MK-4 (less than 0.5% of total pool of intestinal menaquinones) (1). It appears that animal tissues (liver, kidney, possibly brain, pancreas, and salivary glands) produce shorter chain MKs, i.e. MK-3 and MK-4, by conversion of K-1 (2, 3). Thus, unlike the longer chain MKs (MK-6 through MK-11), MK-4 naturally occurs in animal tissues independent of bacterial synthesis.
Dietary sources
• K-1: dark green leafy vegetables, some vegetable oils
• K-2: MK-4 found in meats (particularly liver) and eggs; MK-5 through MK-10 found in fermented plant foods and dairy products.
Some authorities and many textbooks claim that we absorb K2 from bacteria in the colon, but we actually have little direct evidence for this, and given that absorption of K requires the presence of bile acids we have little reason to put faith in this. Moreover, numerous studies indicate that intestinal flora do not provide menaquinones in adequate amounts or in an absorbable form, and deficiencies occur in absence of dietary sources despite colonic flora production of the longer chain menaquinones (1).
Bioavailability
Plant-source phylloquinone (K-1) has a low bioavailability due to its occurring bound in the thylakoid membranes of chloroplasts. We absorb about 80% of isolated K-1, but only about 3% of the K-1 in cooked spinach without fat. Adding fat improves absorption of K-1––we can absorb about 10% of the K-1 if we combine spinach and butter––but still 90% goes unabsorbed (1).
Menaquinones formed by gut bacteria (MK-6 to MK-11) occur in a membrane-bound condition that inhibits absorption (1).
MK-4 embedded in animal fat exhibits a bioavailability more than two fold higher than phylloquinone from spinach (2).
Functions
K-1: blood clotting
K-2: synthesis and activation of bone proteins (osteocalcin)
Dental health
1. Salivary glands contain high concentrations of K2 and may synthesize it.
2. K2 may reduce the bacterial count of saliva (4).
3. Dentin expresses osteocalcin (dependent on VT-A and VT-D) ;VT-K2 activates the ability of this protein to bind calcium.
Bone health
1. K2 required for synthesis of bone proteins (osteocalcin).
2. MK-4 has effects on bone cells not had by K1 (3).
3. Very likely, K2 prevents premature calcification that curtails complete skeletal growth and development (4).
Cardiovascular health
1. K-2 has antiatherogenic effect by inducing NO synthesis.
2. MK-4 appears to inhibit vascular calcification (3).
3. K1 and D combination maintains arterial elasticity
4. A high menaquinone intake reduces the incidence of coronary heart disease.
5. High dietary menaquinone intake is associated with reduced coronary calcification.
Cancer
1. Menaquinones exert growth-inhibitory effects on cancer cells by acting to foster cell-cycle arrest and apoptosis.
2. MK-3 and MK-4 induce apoptosis in leukemia and other malignant cell lines (3).
3. Inverse relationship between K-2 consumption and prostate cancer
Nervous system health
1. K2 makes up between 70 and 93 percent of the VT-K in the brain (4).
2. K2 supports enzymes in brain that produce lipids called sulfatides (4).
3. Autopsies of early stages of Alzheimer’s show 93% lower brain sulfatides. Animals lacking enzymes to make sulfatides suffer from progressive growth retardation, loss of locomotor function, weak legs, seizures (4).
4. VT-K deficiency also appears to alter brain sphingolipid synthesis (3).
Pancreatic health
Pancreas concentrates K2, raising the possibility to that we need K2 for production of digestive enzymes or regulation of blood sugar (4).
Renal health
Kidneys accumulate K2 and secrete VT-K dependent proteins that inhibit formation of calcium salts (4).
Reproductive health
Human sperm secrete K-dependent proteins of unknown function (4).
Drug Interactions
1. Warfarin inihibits K and promotes arterial calcification.
2. Antibiotics act as antagonists to vitamin K.
Nutrient Interactions
1. Vitamins A, D, and K act synergistically in support of skeletal development and health.
2. Vitamin K deficiency increases toxicity of vitamin A and vitamin D.
Toxicity
Non-toxic
Recommendations
1. Type of K2: I presently prefer MK-4 because it is the type synthesized by animal including human tissues.
2. Adequate Dose: Phylloqunione K1, 50-100 mcg/d; MK-4 50-100 mcg/d
3. Source: I consider foods better than supplements since they provide cofactors. However, I don't feel confident that I always get adequate MK-4 from my diet, so I supplement with a combination of K1/K2, 1.0 mg K2 and 0.5 mg K1.
Food Sources
Table modified from Masterjohn (4).
FOOD | VT-K2 (mcg/100g) | % MK-4 |
Natto | 1103 | 0% |
Goose Liver Paste | 369 | 100% |
Hard Cheeses | 76.3 | 6% |
Soft Cheeses | 56.5 | 6.5% |
Egg Yolk (Netherlands) | 32.1 | 98% |
Goose Leg | 31.0 | 100% |
Curd Cheeses | 24.8 | 1.6% |
Egg Yolk (U.S.A.) | 15.5 | 100% |
Butter | 15.0 | 100% |
Chicken Liver | 14.1 | 100% |
Chicken Breast | 9.0 | 100% |
Chicken Leg | 8.5 | 100% |
Ground Beef | 8.1 | 100% |
Bacon | 5.6 | 100% |
Notes
1. Bioavailability and analysis of vitamins in foods
By G. F. M. Ball pp. 255-261.
2. Vitamin and mineral requirements in human nutrition
By World Health Organization, Food and Agriculture Organization of the United Nations. Page 116.
3. Modern nutrition in health and disease
By Moshe Shike. Chapter 20.
4. Masterjohn C. On the Trail of the Elusive X-Factor: A Sixty-Two-Year-Old Mystery Finally Solved. Wise Traditions, Spring 2007.
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