Abstract: Vitamin K presents itself in two primary forms critical to various bodily functions: Vitamin K1 is necessary for proper blood clotting, and Vitamin K2 is essential for proper bone health and development. Since Vitamin K2 is hard to get from dietary sources, it is best to include a supplemental dosage of the K2 form during pregnancy. Vitamin K2 works with calcium and vitamin D3 to ensure your bones stay healthy and your baby's bones develop correctly. 

What is Vitamin K? Why Do I Need It? 

Vitamin K, whether it's for blood clotting, bone mineralization, or energy metabolism, serves many essential functions in the body. This multipurpose fat-soluble vitamin presents in three unique forms: vitamin K1, vitamin K2, and vitamin K3, and each form has its function. 

The relevant forms for pregnancy are Vitamin K1 and Vitamin K2. K1 is important for normal blood clotting, and adequate vitamin stores become increasingly important as the baby's due date gets closer because blood loss during delivery (both vaginal and cesarean) is significant. Adequate intake of vitamin K1 improves optimal blood clotting. K1 cannot be converted into vitamin K2 in sufficient quantities in the body, and thus, vitamin K1 does not affect bone mineralization. It is a sufficient intake of the vitamin K2 form, the most bioactive form of vitamin K, that ensures calcium properly accumulates in bone tissue rather than soft tissue. Your baby's skeleton requires vitamin K2 to develop properly. Vitamin K2 works synergistically with vitamin D3 and calcium in the body to maintain healthy bones. Vitamin K2 is essential for the carboxylation of two Gla proteins, osteocalcin, and matrix Gla protein (MGP), enabling them to bind to calcium and support bone mineralization. The roles of vitamin K2 in bone health have been reviewed, and the Japanese Ministry of Health has approved a synthetic form of short-chain menaquinone (Vitamin K2) as a treatment for osteoporosis. 

Vitamin K2 Working Together With Vitamin D3

The most widely used supplements to support bone health are calcium and vitamin D3. Vitamin D3 increases the intestinal uptake of calcium into the bloodstream. However, an underrecognized critical bone-building vitamin, K2 is needed to activate osteocalcin, allowing osteocalcin to bind calcium and transport calcium from the blood into the bone. Vitamin K2, vitamin D3, and calcium work together to build strong bones. 

The main difference between vitamin K1 and vitamin K2 is their half-lives in the body. Vitamin K1 quickly disappears from circulation, approximately 1-2 hours after consumption. Vitamin K2 has a very long half-life, approximately 2-3 days. This difference in half-life leads to a significant difference in steady-state serum concentration in the body. Vitamin K2 remains in the blood for longer and is far more accessible for organs beyond the liver, such as bone and vessel walls, resulting in adequate bone mineralization. However, vitamin K1 is much easier to obtain from the diet, and intake from food is generally sufficient to activate blood clotting factors fully. In contrast, several studies have demonstrated that osteocalcin and matrix Gla protein in serum are far from fully activated in the general population. Supplementing with vitamin K2 increases the degree of activation of these bone mineralization factors. 

Vitamin K is also involved in energy metabolism. Recent studies have revealed that the bone-specific, vitamin K2-dependent protein osteocalcin closely relates to energy metabolism through insulin sensitivity. 

 Overall, vitamin K2, the calcium helper nutrient, is essential to protect mom's bones, prevent fractures, support dental health and adequately develop your baby's skeleton. Vitamin K2 should be taken alongside vitamin D to help support calcium homeostasis. 

How Should I Get It? 

Since vitamin K1 is so readily available in the diet, vitamin K2 should be the form when supplementing. Vitamin K2 is also known as menaquinones. One pure non-soy form of menaquinone, called MK7, is the preferred supplemental form because it lasts longer in the body. Based on current research, MK7 seems to be the most effective form for improving bone health.

How Much? 

The AI for Vitamin K does not distinguish between the various types of the vitamin and is set at H4: 90 mcg for adult women. This amount was formulated and recommended to ensure normal blood clotting. Research has not incorporated specific vitamin K2 amounts for bone health in its official AI/RDA recommendations, and various organizations recommend different target values. 

National Academy of Medicine US: 90 mcg/day for adult women

The World Health Organization: 55 mcg/day for adult women

European Commission: 75 mcg/day for adult women

Human Nutrition Italian Society: 140 mcg/day for adult women

However, research studies have suggested that a relatively high vitamin K intake is required to include bone and vascular health considerations. Since vitamin K is stored mainly in the liver, where it is used to maintain the normal coagulation balance, a more significant amount is required for other tissues, such as bone. 

Additional Note: Pregnancy does not call for an increased need for the vitamin compared to normal adulthood. 

The Upper Limit for Vitamin K is not established because of its low potential for toxicity. No adverse effects of vitamin K consumption from food or supplements have been reported in humans or animals. 

Am I Getting It From Food? 

Similar to the multiple forms of vitamin K having various functions, the multiple forms of vitamin K have various main food sources as well. 

K1 (Phylloquinone): Found primarily in green leafy vegetables, this is the main dietary form of vitamin K. One cup of raw spinach contains 145 mcg of vitamin K1. A half-cup of raw kale provides 236 mcg of the vitamin. Other significant sources of the vitamin include collards, broccoli, cabbage, mustard greens, swiss chard, and Brussels sprouts. Lastly, some vegetable oils and some fruits can also be a source. 

K2 (Menaquinone): Food sources of this essential form are fatty animal foods, such as full-fat dairy, eggs, and liver, as well as certain fermented foods. One of the richest sources of vitamin K2 is a fermented soybean product called natto. The source of K2 in natto is not the soy itself, but the bacteria used to ferment soybeans. However, this is rarely consumed outside of Asia. Vitamin K2 is harder to get in the diet from foods, as it is present in modest amounts in various animal-based and fermented foods. Gut bacteria produce almost all vitamin K2 in humans. 

For those on a vegetarian diet, obtaining enough dietary K2 can occur through regular consumption of natto, egg yolks, cheese, and fermented dairy products. Hard cheeses that have undergone a long fermentation time, like parmesan, cheddar, and gouda, tend to have higher levels of vitamin K2 than soft, mild cheeses. 

Deficiency

Vitamin K2 deficiency seems to be quite common in the general population. Most prenatal brands listed below contain anywhere from 30 mcg to 100 mcg of vitamin k2 MK7 to help remedy this common deficiency. When studying vitamin K deficiencies, the research discovered that the effects of the deficiency were more prominent in bone health than blood clotting. 

Antibiotic Use 

Those who have taken antibiotics for prolonged periods should be more aware of their vitamin K intake. Antibiotics can destroy vitamin K-producing bacteria in the gut, potentially decreasing vitamin K status. This effect might be more pronounced with cephalosporin antibiotics because these antibiotics might also inhibit the action of vitamin K in the body. 

People with Malabsorption Disorders 

People with malabsorption syndromes and other gastrointestinal disorders, such as cystic fibrosis, celiac disease, ulcerative colitis, and short bowel syndrome, might not absorb vitamin K properly. Vitamin K status can also be low in patients who have undergone bariatric surgery, although clinical signs may not be present. These individuals might need monitoring of vitamin K status and, in some cases, vitamin K supplementation. 

Medical Conditions and Drug Treatments 

Several medication conditions and drug treatments may result in vitamin K deficiency. Treatment with anticoagulants (Warfarin) blocks the body's recycling of vitamin K, resulting in low serum concentrations of vitamin K, affecting bone health in both adults and children. In one experimental study, more than 50% of pediatric patients on warfarin or coumarin were reported to have osteopenia, a condition of weakened bones and decreased bone mass. 

Long-term treatment with anti-inflammatory drugs (corticosteroids) is another example of drugs that negatively affect bone quality. 

How Do I Know If I Am Getting Enough? 

It is hard to measure vitamin K adequately. Historically, the main focus has been on vitamin K1 levels in the body, which are only routinely assessed in those who take anticoagulant medications or have bleeding disorders. Furthermore, blood levels of the vitamin are not very helpful. Compared to other fat-soluble vitamins, minimal amounts of vitamin K circulate in the blood as the vitamin is rapidly metabolized and excreted. Based on phylloquinone vitamin K1 measurements, the body retains only about 30% to 40% of an oral physiological dose. This rapid metabolism accounts for vitamin K's relatively low blood levels and tissue stores compared to the other fat-soluble vitamins. Diet, inflammation and the coexistence of chronic disease are other variables that may impact plasma levels of K1. The only clinically significant indicator of vitamin K status is prothrombin time (the time it takes for blood to clot). Lacking sufficient data, scientific recommendations for intake values of vitamin K2 or ways to measure levels in the body do not exist.

Prenatal Vitamin Brands: What's the Vitamin K Amount and Type in Popular Prenatal Brands?

Prenatal Analysis:

From our research, it is apparent that vitamin K2 is the type of vitamin K that is the most important supplement as it is essential for bone health and not readily found in the diet. The best form of vitamin K2 is menaquinone-7. 

Resources: 

1.     Nichols L. Real Food for Pregnancy: The Science and Wisdom of Optimal Prenatal Nutrition. First edition. Lily Nichols; 2018.
2.     Avena NM, Fear G. What to Eat When You’re Pregnant: A Week-by-Week Guide to Support Your Health and Your Baby’s Development during Pregnancy. First edition. Ten Speed Press; 2015.
3.     Office of Dietary Supplements - Vitamin K. Accessed May 16, 2022. https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
4.     Vitamin K and Osteoporosis - PMC. Accessed May 16, 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7760385/
5.     Møller M, Gjelstad IMF, Baksaas I, Grande T, Aukrust IR, Drevon CA. Bioavailability and Chemical/Functional Aspects of Synthetic MK-7 vs Fermentation-Derived MK-7 in Randomised Controlled Trials. Int J Vitam Nutr Res Int Z Vitam- Ernahrungsforschung J Int Vitaminol Nutr. 2017;87(5-6):1-15. doi:10.1024/0300-9831/a000258
6.     US Pharmacopeial Convention safety evaluation of menaquinone-7, a form of vitamin K - PubMed. Accessed May 16, 2022. https://pubmed.ncbi.nlm.nih.gov/28838081/
7.     Sanguineti R, Monacelli F, Parodi A, et al. Vitamins D3 and K2 may partially counterbalance the detrimental effects of pentosidine in ex vivo human osteoblasts. J Biol Regul Homeost Agents. 2016;30(3):713-726.
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