Fat Soluble Vitamin K

By Cat, June 2007; Updated June 2019

Dr Weston Price, a dentist who studied indigenous people around the world, found that primitive peoples all had a diet rich in fat soluble vitamins, whether they ate largely meat, fish, or vegetables.  These vitamins were found to be A, D and E, plus an unidentified factor Price called “Activator-X” or “X-Factor.” (7K, 8)

Later, it was thought to be part of the Vitamin F category of essential fatty acids, because it was always present in fat.  It is a fat-soluble vitamin, along with vitamins A, D and E, and has a special synergy with vitamins A and D. Eventually, it was given its own name of vitamin K because of its ability to coagulate blood (the Germanic word is “koagulate”).

We now know there are two natural main types of vitamin K, called K1 (phylloquinone), and K2 (menaquinone). Additionally 4 sub-types of K2 have been discovered:  MK4, MK7, MK8, MK9 (the MK stands for menaquinone vitamin K). Price’s X-Factor is now known to be the MK7-form of K2. Who knows what will be discovered next, as this is a growing family!

  • Includes: 1. The Vitamin K Family; 2. Understanding the Differences Between Vitamins K1, K2 and K3; 3. Dietary Sources of Vitamin K; 4. Health Benefits of Vitamin K
  • See Also: 1.Diet & Health Menu; 2. Vitamins: Intro3. Supplements vs Whole Foods (Intro); 4. Vitamin A; 5. Vitamin B complex; 6. Vitamin C7. Vitamin D; 8. Vitamin E9. Vitamin F
  • Other Sites (applicable to vitamin K’s history): 1. Dr Royal Lee and the X-Factor of Dr. Price (Historial archive; (4A)); 2. Butter, Vitamin E and the X-Factor of Dr Price (Historial archive 4B); 3. The Mystery of Butter Oil X-Factor and Vitamin K2: Solved (5B); 4. The Discovery of Vitamin K2 and its Clinical Applications (ncbi study abstract (3))

NOTE:  Consult with your health practitioner before taking any supplements.   Overuse of supplements, just as overuse of drugs, can lead to other health problems, and some supplements can interact negatively with other supplements or drugs.

Remember that the best way to get your vitamins, minerals and other nutrients is from fresh whole foods.

See Vitamins: Intro for:

  • Introduction: Vitamins
  • Vitamin Supplementation vs Whole Foods

The Vitamin K Family

This family has 3 main forms (see illustrations below for K1, K2-MK4 and K2-MK7):

  1. K1 (phylloquinone), found primarily in dark green leafy veggies;
  2. K2 (menaquinone, or MK), found in: fermented foods like natto and cheese, especially curd cheese (e.g. cream cheese and cottage cheese); milk from grass-fed cows* and high-vitamin butter* made from the cream in their milk; and also in meat. It has at least four subtypes (see below).
  3. K3 (synthetic attempt at K2), but should be avoided because it is oxidative (generates free radicals) (7N)

‘* K2 is NOT found in milk of grain/soy-fed dairy; the dairy animals make K2 from nutrients in grass. it is ONLY found in milk of pastured, grass-fed dairy.

Vitamin K2 has four known subtypes that differ by the length of the quinone side-chain:

  1. MK4, found in meat of only grass-fed cows (they convert a substance in the grass to MK4; it cannot be made from grain and/or soy-fed cows); it is also available in supplement form. (5E)
  2. MK7, found in fermented foods and available in supplement form (5E); it is the vitamin Dr. Price called “Activator X” or the “X-Factor.”
  3. MK8, found in fermented foods.
  4. ML9, found in fermented foods.

The following sketches are for K1, K2-MK4, and K2-MK7, as indicated (from Wikimedia Commons (15B)). K2 differs from K1 primarily by adding double bonds along the side-chain; the MK versions differ from each other by length of the side-chain. See Wikipedia: Vitamin K (15A) article for more.

Understanding Differences Between Vitamin K1, K2 and K3

Vitamin K is such an important vitamin that, although I don’t typically recommend adding many extra supplements to your diet, vitamin K is of the few supplements you should seriously consider because many people don’t get nearly enough of it on a daily basis through the foods they eat.

The main functions that K1 and K2 have in common are blood clotting, heart health and bone health. However, understanding the different types and how they work is very important.

About Vitamin K1: This form is made by plants (especially grass), and was the first form to be discovered. It was named from Koagulant, the German word for coagulant, because its major function is to coagulate blood. It can help to prevent excessive bleeding, as in when blood thinners or coumadins cause improper clotting, or to treat prothrombin deficiencies caused by external factors like a blood thinner. It may also help with bone density and cancer prevention (11).

It is poorly absorbed by the human body – only about 10% (13), perhaps because it does not come from fatty foods, and is not often eaten with fat, which otherwise improves its absorption (12).

About Vitamin K2 is also believed to be Weston Price’s “activator X’ in raw milk from grass fed cows (and not found in milk of grain-fed cows), according to the Real Milk website (5A). NOTE also that vitamin K is only in the butterfat portion of milk, so to get the max, drink whole raw milk. Also, kefir, which is fermented, has more vitamin K than milk. See Chris Masterjohn’s article: On the Trail of the Elusive X-Factor: a 62-Year Old Mystery Finally Solved (from 2008) (5E), which is one of several articles in the journal:  Dr Price’s X-Factor: Mystery Solved (5D) for lots of info about vitamin K2, including a good list of foods that contain K2, and amounts in those foods.

If you plan to get your K2 from dairy, it is best to consume it raw or fermented, as pasteurization destroys much of the vitamin content.

K2 is more readily absorbed by our body than K1, likely because it comes from fatty foods. (12).  MK-4 appears to be better at protecting your tissues from cancer, calcium deposits, and sex hormone production. MK-7 is good at reaching bones and supporting their health while also improving hormonal and metabolic function and supporting blood clotting (13). See Health Benefits, below, for more on this.

About Vitamin K3: After the discovery of vitamin K2, attempts to make it synthetically failed, but the end result, menadione, is considered a precursor to K2, and was named K3Much of the research on vitamin K has focused on synthetic vitamin K3 taken at high doses, and it is commonly being used with chemotherapy agents for enhanced effectiveness. It is also added to pet and animal feed. (14)

However, K3 is synthetic and is generally regarded as toxic because it generates free radicals, that can damage internal organs such as the kidneys and the liver. It is banned for human consumption in most economically developed countries (except the US), but is still added to animal feed, including pet food. I strongly advise against using it, and seek out pet foods that do not contain it. [Look for “K3” or “menadione” on pet food labels.] (14)

See Dietary Sources section, below, for natural sources of vitamin K, including n supplements.

See also: Mercola’s sales-pitch for his vitamin K products for lots of good information (types, what it does, where to get it, etc.) (7M)

Dietary Sources of Vitamin K

Important note: Vitamin K and vitamin D work together to support your cardiovascular health, your bone health, and your immune system among many other functions. Vitamin D can’t work properly without vitamin K, and vitamin K can’t perform its actions without enough vitamin D. You need both, and in the proper amounts. …  [If you] take high doses of  vitamin D… [and] fail to get enough K, you can raise your risk of arterial calcification.” (7M) I believe this includes all forms of vitamin K.

Similarly, vitamins A and D work together, especially with the help of vitamin E.

Vitamin K1:

Daily dosage: No recommended daily dosage of K1 has been established; however it is recommended to eat a minimum of 200 grams of vegetables, especially green, leafy veggies each day. (7Q)

Foods: K1 makes up about 90 percent of the vitamin K in a typical Western diet. As mentioned above, K1 is found primarily in dark green leafy veggies, such as spinach, lettuces, arugula, collard greens, salad greens, kale, broccoli, Brussels sprouts, and cabbage. One should consider eating these frequently, as long as they correspond to your nutritional type (see Mercola article (7O) for more about nutritional types); I’m a “Protein Type.”

Supplemental K1 is also available, but I have not been familiar with them. Beginning June 2019, I am trying out a Thorne Vitamin K supplement (iHerb code THR-00661) that includes K1 (1 mg), MK4 (5 mg) and MK7 (90 mcg) per capsule.

Vitamin K2:

Daily dosage recommendation: 360-500 micrograms (mcg) of vitamin K2 per day. (7Q)

Foods: K2 makes up only about 10 percent of Western vitamin K consumption, mainly because we don’t eat enough fermented foods. If we have a healthy gut (most who eat a Western diet do not have healthy gut microbiome), we get the rest as made by our intestinal bacteria. It is then absorbed from the small intestine.


  • MK4 is found in meat of grass/pasture-fed animals, but NOT in soy/grain-fed animals.
  • MK 7, MK8, and MK9 subforms are found primarily in fermented foods such as natto (fermented soy), kefir (if made from raw milk of grass-fed dairy animals), butter from grass-fed dairy animals, and cheese. Such foods typically have the highest concentration of vitamin K found in the human diet, and can provide several milligrams of vitamin K2 daily. This level far exceeds the amount of K1 found in dark green vegetables. Daily, I get approximately 4.8 mg K2 from the following:
    • brie cheese, about 1 oz which provides about 0.6 mcg K2
    • cottage cheese, about ¼ cup which provides about 3 mcg K2
    • butter, about 2 Tbsp which provides about 1.2 mcg K2,

Important consideration: “fermented foods contain a wide variety of different bacteria, and only certain ones—such as Bacillus subtilis—actually make vitamin K2. You can boost the K2 content of fermented foods by making them yourself, using a starter culture specifically designed to optimize K2.” (7Q)

Supplemental K2 is also available; for example, a few brands I trust (NOTE: If you are taking anticoagulants such as Warfarin (Coumadin), DO NOT USE K2 supplements):

  • K1, K2 mix: Thorne Research, 3K Complete in capsule form, contains K1, MK4 and MK7 (THR-00661) June ’19: I am trying this to see if it helps with “gravel” in my kidneys, among other benefits.
  • K2-mix:
    • Green Pastures, X-Factor Gold Concentrated Butter Oil (see Amazon ASIN B002LZDQD0), or Green Pastures, Fermented Cod Liver Oil and Concentrated Butter Oil Blend (see Amazon ASIN B07256LN65 for capsules or ASIN B004QCMGTG for liquid). In this whole-food supplement, vitamin K2 is not added but rather is a natural part of the butter oil, so likely contains MK7, MK8, and MK9. Former name of this product was High-Vitamin Butter Oil, which was a term coined by Dr. Weston A. Price.
    • California Gold Nutrition, Full Spectrum Vitamin K2 capsules include MK4, MK6, MK7 and MK9 (iHerb code CGN-01299); NOTE: I have no experience with this brand, but it is the least expensive vitamin K2 supplement.
  • MK4: Thorne Research:
    • Vitamin K2-MK4 liquid (iHerb code THR-17001) provides 1 mg MK4 per drop, or
    • Vitamins K2 and D3 mix (iherb code THR-50001) provides 100 mcg MK4 and 13 mcg (500 IU) D3 per drop.
  • MK7:
    • Douglas Laboratory offers Vitamin K2-MK7 in capsule form, 90 mcg/cap (Amazon ASIN B0058A9PSA)
    • Mercola Vitamin K2-MK7 in capsule form, 150 mcg/cap (iHerb code MCL-01532)
  • Vitamin D and K2 mix supplements are also available.

Vitamin K3:

This synthetic form of K2 is not found in any whole foods (though it may be added to processed foods). It can be found in some lower-quality multi-vitamin supplements. However, K3 has serious issues in our bodies and should be avoided. For example, it may be toxic by interfering with the function of glutathione, the primary detox agent in the liver (15A).

About High-Vitamin Butter Oil

The following is from Radiant Life (16A), to which I add a 6th bullet item: Vitamin K

Essential Components of High Vitamin Butter Oil [such as in Green Pastures brand, X-Factor Gold Concentrated Butter Oil, or their Fermented Cod Liver Oil and Concentrated Butter Oil Blend]

  • CLA (Conjugated Linoleic Acid): Facilitates normal cellular growth and metabolism. CLA has also been found to help enhance muscle growth, promote normal blood sugar levels and support a healthy immune system. Naturally occurring CLA is six times more effective than synthetically produced CLA. [It is one of the few natural trans-fatty acids that are beneficial.]
  • Wulzen Factor: Supports joint health and function. Called the “anti-stiffness” factor, researcher Dr. Rosalind Wulzen discovered that this substance helps protect humans and animals from calcification of the joints. Additionally, it protects and supports the circulatory system, ocular (eye) membranes, and pineal (the “master” gland) health. The Wulzen factor is found in unpasteurized dairy products, but it is destroyed at high temperatures [such as pasteurization].
  • Butyric Acid
  • Soothes intestinal wall cells irritated by the penetration of roots/rhizoids of Candida Albicans overgrowth (leaky gut syndrome). An important energy source for the cells lining the G.I. tract. [It is available in three forms: butyric acid, tributyrin and butyrate; tributyrin is the form in butter.][see also Cat’s article Butyrate]
  • Vitamin A: Aids digestion of protein, minerals and water-soluble vitamins. Essential for numerous biochemical processes. Dr. Price’s research found that protein, minerals, and water-soluble vitamins cannot be utilized without vitamin A from animal sources. (Though carotene from plants can convert to vitamin A, many people – particularly infants, children, diabetics and those with poor thyroid function- cannot make this conversion). Vitamin A is also a powerful antioxidant, protecting the body from pollutants and free radicals. It aids protein digestion by stimulating secretion of gastric juices and plays a vital role in building strong bones and blood.
  • Vitamin D: Assists with maximum calcium absorption. Vitamin D is essential for strong bones, healthy teeth and normal growth. Dr. Price found that healthy native peoples’ diets were rich in vitamin D from foods like butterfat, eggs, liver, organ meats, marine oils and seafood.
  • Vitamin K [this info added by Cat]: This is the main topic of this post on Vitamin K. It is present in cultured (fermented) butter from milk of grass-fed/pastured dairy. See it’s health benefits, below. See also The Mystery of X-Factor Butter Oil and Vitamin K2: Solved! (16B)

Health benefits of Vitamin K

This list is for the vitamin K-family, in general (I didn’t keep track of the sources for most benefits in this list); see below for benefits specific to K2.

  • Promote your heart health
  • Helps with arterial plaque
  • Protect and support your skin
  • Help regulate calcification of your tissues
  • Boost your overall immune system
  • Provide powerful antioxidant benefits
  • Protect your cells against oxidative damage
  • Aid in supporting your already normal blood sugar levels
  • Fight cancer with Vitamin K (7L)

Benefits of Vitamin K2:

Unless noted otherwise (with a different reference number), the following is Cat’s notes from Chris Masterjohn’s article regarding Activator X (5E), which is now known to be vitamin K2-MK7. Note: see Chris’s references for the quoted text from his article (I did not copy his references in my notes).

In the following, “vitamin D” refers to the natural form of D3 created from cholesterol in the skin with the help of radiation from the sun, and the supplemental form of D3 .

‘1. Synergy with vitamin D: “Price showed Activator X to exhibit dramatic synergy with vitamins A and D. … Vitamin K2 is the substance that makes the vitamin A- and vitamin D-dependent proteins come to life. While vitamins A and D act as signaling molecules, telling cells to make certain proteins, vitamin K2 activates these proteins by conferring upon them the physical ability to bind calcium.” [he gives osteocalcin as an example].

[Note that while he includes vitamin A in the synergy, it often has the opposite effect of vitamin D, and also the two must be in the correct balance. See my article, Vitamin A, which includes a section on A:D ratio.]

    • “Vitamin K2 may also be required for the safety of vitamin D.” (5E)
    • From Mercola (7T):
      • “Evidence shows that vitamin D is dependent on vitamin K, and that vitamin D3 toxicity is actually caused by vitamin K2 deficiency.”
      • Think of vitamin D as the gatekeeper, controlling who gets in, and vitamin K2 as the traffic cop, directing the traffic to where it needs to go.” I other words, Vitamin D lets calcium into the bloodstream, but without vitamin K2 directing it into tissues where it is needed, the calcium could build up on your coronary arteries, rather then being incorporated into your bones.
      • If you take Vitamin D3 and calcium, but are deficient in vitamin K, “you could be worse off than if you were not taking those supplements at all.

2. On dental health:Weston Price was primarily interested in Activator X because of its ability to control dental caries. … [he] used the combination of high-vitamin cod liver oil and high-Activator X butter oil as the cornerstone of his protocol for reversing dental caries.

    • Activator X [now known to be vitamin K2] also influences the composition of saliva” [specifically the level of phosphorus].

Notes about the primary brand for these supplements, Green Pastures:

    • They are now called “Concentrated Fermented Cod Liver Oil” and “Concentrated Butter Oil.”
    • The former is the oil from fermented cod livers (the oil itself is not fermented, contrary to what Dr. Ron asserts);
    • The latter is from fermented butter made from the milk/cream of pastured cows.

3. On bone health: Vitamin D is “important to the functional quality of bone and the ability to regulate its shape.” See also Synergy with Vitamin D, above.

    • “… vitamin K2 is the preferred K vitamin of the bones. It takes one milligram per day of a highly absorbable pharmacological preparation of vitamin Kto maximally activate osteocalcin in human subjects; it appears, however, that humans are not capable of absorbing much more than one fifth this amount from whole foods. By contrast, large amounts of vitamin K2 are readily absorbed from foods.”
    • Helps with bone-building by osteoblasts (more on this, below): K2 is key to producing osteocalcin protein, the structure that holds calcium in place in the bones. And it also keeps osteoclasts (that tear down bone) in check. Works with vitamin D3 for improved bone health [see “Synergy with Vitamin D” above.]
    • K2 provides the “pass key” to move calcium and other minerals from your bloodstream to your bones (7N). See Mercola’s article, “The Key Vitamin for Bone Health that Most People Don’t Know About” (7N) for more detail.]
    • See also the section “More on Vitamin K2 and Bone Health,” below.

4. On heart health:Research is in fact rapidly redefining heart disease largely as a deficiency of this vitamin. While it is most clearly established that vitamin K2 deficiency causes calcification of the cardiovascular system, vitamin K2 appears to protect against the inflammation and accumulation of lipids and white blood cells that characterize atherosclerosis as well.”

    • One “vitamin K-dependent protein … guards … against the formation of crystals by the calcium that circulates in the blood.
    • Two “vitamin K-dependent proteins are likely to play a role in the development of atherosclerosis

5. On brain health:

    • “The brain contains one of the highest concentrations of vitamin K2 in the body; only the pancreas, salivary glands, and the cartilaginous tissue of the sternum contain more.”
    • An analysis of three autopsies showed that vitamin K2 makes up between 70 and 93 percent of the vitamin K in the human brain.”
    • “Vitamin K2 supports the enzymes within the brain that produce an important class of lipids called sulfatides. The levels of vitamin K2, vitamin K-dependent proteins and sulfatides in the brain decline with age; the decline of these levels is in turn associated with age-related neurological degeneration.”
    • “…deficiencies in vitamin K, especially vitamin K2, could result in fatigue and learning difficulties in humans, and that rare, extreme deficiencies of vitamin K2 in the brain could result in seizures.”

6. On kidney stones:

    • K2 is important for prevention of kidney stones. “The kidneys … accumulate large amounts of vitamin K2 and secrete vitamin K-dependent proteins that inhibit the formation of calcium salts. Patients with kidney stones secrete this protein in its inactive form, which is between four and twenty times less effective than its active form at inhibiting the growth of calcium oxalate crystals, suggesting that vitamin K2 deficiency is a major cause of kidney stones.
    • Cat’s note: The synthetic form K3, is known to cause kidney stones, so is not a good replacement for K2. See “About K3” in the “Understanding Differences Between Vitamin K1, K2 and K3” section, above, for more on this.

7. Other roles of Vitamin K2:

    • Play “a role in activation of digestive enzymes in the salivary glands and pancreas.”
    • “Vitamin K2 has powerful anti-carcinogenic properties that may make it useful in preventing or treating cancer in humans,” including lung (3A), prostate (7S) and liver cancers (7S). See also (7L)
    • Vitamin K deficiency may interfere with insulin release and blood sugar regulation in ways similar to diabetes (7R).

More on Vitamin K2 and Bone Health

The following are my notes/quotes from Mercola’s 2009 article: The Key Vitamin for Bone Health that Most People Don’t Know About (7N). Mercola’s original article does not specify the form of vitamin K, but in a related 2013 article (7P), he indicates it is K2. Chris Masterjohn (9) agrees. PLT Health (10) agrees and goes further to suggest it is the forms MK7, MK8, and/or MK9. Here’s my notes from the original 2009 Mercola article (7N).

Vitamin K is most well known for the important role it plays in blood clotting. However, it also activates a specific protein known as osteocalcin, which acts as a kind of glue that helps to incorporate calcium into your bones. Vitamin K is necessary in order to produce this protein.

In addition to being involved in the formation of osteocalcin, vitamin K is involved in the formation of matrix Gla-protein (MGP). MGP is synthesized in a vitamin K-dependent way in smooth muscle cells of the healthy vessel wall. The forms of vitamin K involved

According to Professor Vermeer, MGP is a hot topic right now because it is the most powerful inhibitor of soft-tissue calcification presently known, and it needs vitamin K to be active in that way.

Vessel walls have only MGP to defend themselves against calcification, which is the hardening of the arteries that leads to atherosclerosis (coronary artery disease) and heart failure.

In fact, in people who don’t get enough vitamin K, about 30 percent of your body’s potential MGP is not activated, which means your protection against calcification of vessels is 30 percent less than optimal. This can play a major role in your risk of heart disease, especially if you have other risk factors.

Check out the following (I’ve not yet had a chance to do this):


References 1 – 6 are common to all my vitamin pages; those specific with vitamins E and K begin with number 7.

  1. well.blogs.nytimes.com/2008/02/06/despite-risks-vitamins-popular-with-cancer-patients/
  2. (6) dailyyonder.com/four-food-groups/2010/03/04/2623
  3. ncbi abstracts (3B – 3G originally cited in Supplements for Insulin Resistance, as numbers 21A – 21F)
    1. (new) ncbi.nlm.nih.gov/pubmed/23183291
    2. (21A in Supplements for IR) ncbi.nlm.nih.gov/pubmed/7622343
    3. (21B) ncbi.nlm.nih.gov/pubmed/6278902
    4. (21C) ncbi.nlm.nih.gov/pubmed/22986984
    5. (21D) ncbi.nlm.nih.gov/pubmed/9169302
    6. (21E) ncbi.nlm.nih.gov/pubmed/3017301
    7. (21F) ncbi.nlm.nih.gov/pubmed/8131066
    8. (9A) ncbi.nlm.nih.gov/pubmed/19091068 for Nutrition Journal, December 17, 2008 on PubMed
    9. (new) ncbi.nlm.nih.gov/pubmed/12888897
  4. Selene River Press, by and about Dr Royal Lee, regarding Dr W. A. Price’s XFactor:
    1. Dr Royal Lee’s original article on Dr Weston A. Price’s XFactor: seleneriverpress.com/historical/dr-royal-lee-on-the-x-factor-of-dr-weston-a-price/; or see the original article: 6sd6hj41ya-flywheel.netdna-ssl.com/images/pdfs/40_weston_price_vitamin_f.pdf (I’ve also saved it as a pdf: CATSFORK > PDF FILES / Price-VitaminF-XFactor_Dr RoyalLee.pdf)
    2. Butter, Vitamin E, and the X-Factor (historical archive of Dr Lee’s article) (seleneriverpress.com/historical/butter-vitamin-e-and-the-x-factor-of-weston-a-price/)
    3. Lectures of Dr. Royal Lee, Vitamin News (seleneriverpress.com/shop/lectures-of-dr-royal-lee-volume-i-pdf-ebook/
    4. Vitamin News, a collection of all the biannual issues in one book: (seleneriverpress.com/shop/vitamin-news/
    5. SRP Historical Archives:  seleneriverpress.com/srp-historical-archives/
  5. Articles on The X-Factor of Dr. Weston A. Price:
    1. Brochure: Campaign for Real Milk (http://www.realmilk.com/what.html
    2. (5) realmilk.com/health/x-factor-vitamin-k2/
    3. (6) blog.radiantlifecatalog.com/bid/59999/The-Mystery-of-X-Factor-Butter-Oil-and-Vitamin-K2-Solved
    4. Dr Price’s X-Factor: Mystery Solved – a Journal of articles
    5. On the trail of the elusive x-factor: a 62-year old mystery finally solved, by Chris Masterjohn (westonaprice.org/health-topics/abcs-of-nutrition/on-the-trail-of-the-elusive-x-factor-a-sixty-two-year-old-mystery-finally-solved/ [The original link is no longer valid: westonaprice.org/abcs-of-nutrition/fat-soluble-activators/175-x-factor-is-vitamin-k2]
  6. More articles by Dr. Royal Lee: soilandhealth.org/wp-content/uploads/02/0203CAT/royal.lee.lets.live.articles.htm
  7. Mercola: differences from vitamin b list begins here
    1. (A7) Vitamin D links: articles.mercola.com/sites/articles/archive/2008/12/23/important-cod-liver-oil-update.aspx
    2. (D1) articles.mercola.com/sites/articles/archive/2008/12/27/important-vitamin-d-update.aspx
    3. (D2) articles.mercola.com/sites/articles/archive/2011/12/14/study-shows-vitamin-d-cuts-flu-by-nearly-50.aspx
    4. (D6) articles.mercola.com/sites/articles/archive/2011/12/19/why-are-cancer-cases-rising-by-nearly-50-in-the-next-20-years.aspx
    5. (D7) articles.mercola.com/sites/articles/archive/2009/12/01/Important-New-Vitamin-D-Research-Papers.aspx
    6. (D8) articles.mercola.com/sites/articles/archive/2011/11/13/vitamin-d-for-depression.aspx
    7. (D10) articles.mercola.com/sites/articles/archive/2008/11/18/do-flu-shots-work-ask-a-vaccine-manufacturer.aspx
    8. (D15) articles.mercola.com/sites/articles/archive/2008/02/12/why-vitamin-d-supplements-are-not-the-same-as-sunlight.aspx
    9. (new) products.mercola.com/vitamin-d-supplement/
    10. (new) mercola.com/article/vitamin-d-resources.htm
    11. Vitamin K, or D and K links: (new) articles.mercola.com/sites/articles/archive/2003/10/08/cancer-vitamin-k.aspx
    12.  articles.mercola.com/sites/articles/archive/2004/03/24/vitamin-k-part-two.aspx
    13. products.mercola.com/vitamin-k/
    14. articles.mercola.com/sites/articles/archive/2009/06/13/The-Key-Vitamin-for-Bone-Health-that-Most-People-Dont-Know-About.aspx
    15. products.mercola.com/nutritional-typing/
    16.  articles.mercola.com/sites/articles/archive/2013/10/19/vitamin-d-vitamin-k2.aspx
    17. Vitamins K1 and K2, the Under-appreciated Nutrients that are Critical for Health: articles.mercola.com/sites/articles/archive/2015/01/11/vitamin-k1-k2.aspx
    18. articles.mercola.com/sites/articles/archive/2010/06/19/vitamin-k-linked-to-lower-diabetes-risk.aspx
    19.  articles.mercola.com/sites/articles/archive/2008/05/03/the-vitamin-you-need-to-prevent-prostate-cancer.aspx
    20. articles.mercola.com/sites/articles/archive/2011/03/26/the-delicate-dance-between-vitamins-d-and-k.aspx
  8. Washington Post: The Great Divide, on Sally Fallon’s story:
    1. Part 1: washingtonpost.com/wp-dyn/content/article/2008/08/05/AR2008080501000.html
    2. Part 2: washingtonpost.com/wp-dyn/content/article/2008/08/05/AR2008080501000_2.html
  9. Chris Masterjohn, PhD: chrismasterjohnphd.com/blog/2016/12/09/the-ultimate-vitamin-k2-resource/
  10. PLT Health Solutions: plthealth.com/news/articles/vitamin-k-required-inhibit-calcium-accumulation-arteries-new-paper-thrombosis-and
  11. Fit Day: fitday.com/fitness-articles/nutrition/vitamins-minerals/the-function-of-vitamin-k1.html
  12. Healthline: healthline.com/nutrition/vitamin-k1-vs-k2#section8
  13. Naturally Savvy: naturallysavvy.com/care/vitamin-k-function-deficiency-sources/
  14. WiseGeek: wisegeek.com/what-is-vitamin-k3.htm
  15. Wikipedia:
    1. en.wikipedia.org/wiki/Vitamin_K
    2. image: commons.wikimedia.org/wiki/File:Vitamin_K_structures.jpg
  16. Radiant Life:
    1. blog.radiantlifecatalog.com/bid/39391/What-is-the-X-Factor-High-Vitamin-Butter-Oil
    2. blog.radiantlifecatalog.com/bid/59999/The-Mystery-of-X-Factor-Butter-Oil-and-Vitamin-K2-Solved (this is a duplicate of reference 5C)

Articles about X-factor and Vitamin K2:

  • Dr Royal Lee and the X-Factor of Dr. Price (Historial archive; (4A)); 2. Butter, Vitamin E and the X-Factor of Dr Price (Historial archive 4B); 3. The Mystery of Butter Oil X-Factor and Vitamin K2: Solved (5B); 4. The Discovery of Vitamin K2 and its Clinical Applications (ncbi study abstract (3A))

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