Vitamin K Supplements Review (Including Calcium and Vitamin D)
Initial Posting: 5/20/17 Last Update:6/8/17
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What It Is:
- What is it? Vitamin K helps with proper blood clotting as well as with calcium utilization in bones and the cardiovascular system (See What It Does).
- Do you need to take it as a supplement? Most people are not deficient in vitamin K and symptomatic deficiency is rare, so unless you have a malabsorption condition or are severely malnourished, you likely get sufficient vitamin K from your diet (e.g., from green leafy vegetables, dairy, and fermented foods -- see Vitamin K from food). Vitamin K supplements have been clinically tested to increase bone density and reduce fractures, as well as to improve cardiovascular function, but results have been mixed, so it is not clear that supplementation will help (see What It Does).
- Which form? There are several forms of vitamin K. All are active, but one, the MK-7 form of vitamin K2, can increase blood levels of vitamin K up to 8 times as much as other forms. It's generally more expensive than the others, but it likely that you can take less of it (see What It Is and What to Consider When Buying).
- How much to take? An adequate daily intake of vitamin K for an adult is 100 mcg. It is difficult to know what dose may be useful in bone health (or if any dose is truly beneficial). However, studies involving supplements containing K1 or the MK-4 form of K2 tend to use very high doses (e.g., 500 mcg to 45,000 mcg), while studies with the MK-7 form of K2 have used more moderate dosing, e.g., 180 mcg. (See What to Consider When Using).
- How to take it Vitamin K is fat soluble, so you'll absorb more of it when you take it with a meal that has fats or oils. Other fat soluble vitamins, like vitamin D, can compete with its absorption, so take them at least 3 hours apart. (See What to Consider When Using).
- Best choice? Products vary in quality and cost (See What CL Found). Among Approved products, ConsumerLab.com identified several which represented its Top Picks.
- Cautions: Vitamin K is fairly safe. However it can interact with certain medications. If you have an allergy to soy, be aware that most MK-7 forms of vitamin K are derived from soy, (See Concerns and Cautions). One branded form of MK-7 (MenaQ7) is derived from chickpeas and claims to be soy-free (See What It Does), although a product containing this form did not pass testing (See What CL Found).
Vitamin K is a group name for a number of structurally related, fat-soluble vitamins including K1 (phylloquinone or phytonadione) and the K2 vitamin subgroup (menaquinones). Vitamin K1 is the primary dietary source of vitamin K and is found at high levels in green leafy vegetables and, in lower levels, in vegetable oils. Vitamin K2 is found, typically in small amounts, in butter and some cheeses and is produced by bacteria in the intestines from vitamin K1, although it is unclear how much vitamin K this contributes to the body. There are several forms of vitamin K2 (designated as menaquinones-1 through -10 or MK-1 through MK-10).
All forms of vitamin K are active in humans. Vitamin K1 (synthetically produced) was traditionally the most common form of vitamin K in dietary supplements. However, vitamin K2 in the form of menaquinone-7 (MK-7) is believed to have a longer half-life time than vitamin K1, resulting in much more stable serum levels and accumulation of MK-7 to higher levels (7- to 8-fold) during prolonged intake (1). Consequently, K2 has become popular in supplements, despite higher cost as an ingredient. MK-7 is typically obtained from natto, a popular Japanese food product made from fermented soybean. In supplements, natto-derived MK-7 is sometimes called "natural MK-7." New synthetic forms of MK-7 have become available and also have a long half-life, although it is not clear if these have the same bioactivity as MK-7 from natto. These new forms are synthesized from flower extracts such as geraniol or famesol.
Another form of vitamin K2, known as menaquinone-4 (or MK-4), is produced in certain animal tissues and can occur in small amounts in meats and egg yolk and, when produced synthetically, is used in some supplements. MK-4 is absorbed as well as MK-7 but it has a shorter half-life. Other forms of vitamin K exist but are generally not sold as supplements.
For more information on how the forms of vitamin K are best used see ConsumerTips.
(See separate reviews of Calcium and Vitamin D, which are also used in bone health).
What It Does:
Vitamin K functions in the body to modify certain proteins that ensure proper blood clotting and calcium utilization in the bones and cardiovascular system.
There is evidence that low vitamin K consumption or impaired vitamin K status is associated with lower bone mass and higher risk of hip fracture among older individuals. However, clinical trials with various vitamin K supplements have shown either modest or no benefit in preventing bone loss.
Studies with vitamin K1 alone have generally not shown much improvement in bone density, although a large study showed that people taking high dose (1,000 mcg) vitamin K1 along with calcium, vitamin D and magnesium supplements showed less bone loss than those taking the same supplements without vitamin K1 or taking only placebo. Another large study using a somewhat lower daily dose (500 mcg) of vitamin K1 per day plus calcium (600 mg) and vitamin D (400 IU) did not show benefit.
Some clinical trials in Japan reported that very high doses (45,000 mcg) of the menaquinone-4 form (MK-4) of vitamin K2 improved bone mineral density and reduced fracture risk in women. However, other studies found no effect.
A three-year, placebo-controlled study with low-dose MK-7 (180 mcg per day) in healthy postmenopausal women in the Netherlands found that MK-7 intake decreased the age-related decline in bone mineral content and density at the lumbar spine and femoral neck, but not for the total hip (Knapen, Osteoporo Int 2013). Bone strength was also favorably affected by MK-7. Improvements were statistically significant after 3 years, but not earlier. Calcium and vitamin D supplements were not given as part of this study.
Vitamin K1 is known to be effective in preventing and treating poor blood clotting (hypoprothombinemia) caused by vitamin K deficiency or induced by certain medications. Vitamin K2 has also been shown to be effective and apparently, more potent.1 Symptomatic vitamin K deficiency, however, is rare — resulting from severe malnutrition or malabsorption, or prolonged therapy with some antibiotics.
Low serum vitamin K levels have been associated with atherosclerosis. Higher intake of vitamin K2 (particularly the MK-4 form) from the diet (mainly from cheese) is associated with reduced risk of coronary calcification and mortality from coronary heart disease (Geleijnse, J Nutr 2004; Beulens, Atherosclerosis 2009). These benefits have, so far, not been proven with vitamin K2 supplements, although one double-blind study found that 180 mcg of MK-7 (MenaQ7, NattoPharma ASA — found in Doctor's Best Artery Prime With MenaQ7 in this review) taken daily for three years reduced arterial stiffness in healthy postmenopausal women, especially in those with high arterial stiffness. However, there was no effect on endothelial dysfunction, which is closely associated with cardiovascular events such as heart attack (Knapen, Thromb Haemost 2015).
Most research suggests vitamin K1 does not have a similar cardiovascular benefit as K2, although one study showed that people with pre-existing coronary artery calcification who took a multivitamin including vitamin K1 for three years had 6% less progression of calcification than those who received the multivitamin without K1. However, among people without pre-existing calcification, an equal percentage developed calcification regardless of whether or not they received vitamin K1 (Shea, Am J Clin Nutr 2009).
A multi-year population study showed that people who consumed larger amounts of foods (such as cheese) known to contain vitamin K2 had a statistically lower risk of dying from cancer. Men (but not women) also had a statistically significant decrease in the incidence of cancer, particularly prostate and lung cancers. No such associations were found for the consumption of foods containing vitamin K1.2
For more information about the uses of vitamin K, see the Vitamin K article in the Natural Products Encyclopedia on this Web site.
Quality Concerns and What CL Tested for:
Like other supplements, neither the FDA nor any other federal or state agency routinely tests vitamin K supplements for quality prior to sale. However, quality issues can include the following:
As part of its mission to independently evaluate products that affect health, wellness, and nutrition, ConsumerLab.com purchased vitamin K supplements (including those with calcium, vitamin D, and/or magnesium) sold in the U.S. These were tested to determine whether they 1) possessed the claimed amounts of vitamin K, calcium, vitamin D, and magnesium, 2) were free from unacceptable levels of lead, cadmium and arsenic, and 3), if in tablet form, were able to break apart fully within an expected period of time in disintegration testing (see Testing Methods and Passing Score).
- Labeled Amount -- Does the product really contain the labeled amount and form of vitamin K? Vitamin K, particularly the MK-7 form of K2, can be an expensive ingredient, providing economic incentive for a manufacturer to put in less (or a less expensive form) than what is claimed.
- Purity -- Many vitamin K supplements include calcium which may naturally be contaminated with heavy metals such as lead, cadmium or arsenic. In children, infants, and fetuses, even low levels of lead can adversely affect neurobehavioral development and cognitive function. In adults, lead at somewhat higher levels can cause elevated blood pressure, anemia, and adversely affect the nervous and reproductive systems. Lead is of particular concern during pregnancy as the mother can deliver it to the fetus. Cadmium is a carcinogen and kidney toxin. Arsenic is a carcinogen and can damage organs.
- Ability to Break Apart for Absorption -- For a tablet to be most useful, it must fully disintegrate prior to leaving the stomach, delivering its contents for absorption in the gut. Some tablets are not properly made and can pass through your body completely or partially intact, depriving you of its ingredients. Remnants of such products are sometimes found in the stool. This happens, for example, when a tablet is too tightly compressed (too "hard") or is too thickly coated.