This can be a reality sheet meant for well being professionals. For a reader-friendly overview of Vitamin Ok, see our shopper reality sheet on Vitamin Ok.
COVID-19
Introduction
“Vitamin K,” the generic identify for a household of compounds with a typical chemical construction of 2-methyl-1,4-naphthoquinone, is a fat-soluble vitamin that’s naturally current in some meals and is out there as a dietary complement [1]. These compounds embrace phylloquinone (vitamin K1) and a collection of menaquinones (vitamin K2) [2]. Menaquinones have unsaturated isoprenyl aspect chains and are designated as MK-4 by MK-13, primarily based on the size of their aspect chain [1,2]. MK-4, MK-7, and MK-9 are essentially the most well-studied menaquinones.
Phylloquinone is current primarily in inexperienced leafy greens and is the primary dietary type of vitamin Ok [3]. Menaquinones, that are predominantly of bacterial origin, are current in modest quantities in varied animal-based and fermented meals [1,4]. Virtually all menaquinones, particularly the long-chain menaquinones, are additionally produced by micro organism within the human intestine [5,6]. MK-4 is exclusive in that it’s produced by the physique from phylloquinone through a conversion course of that doesn’t contain bacterial motion [7].
Vitamin Ok features as a coenzyme for vitamin Ok-dependent carboxylase, an enzyme required for the synthesis of proteins concerned in hemostasis (blood clotting) and bone metabolism, and different numerous physiological features [3,5]. Prothrombin (clotting issue II) is a vitamin Ok-dependent protein in plasma that’s immediately concerned in blood clotting. Warfarin (Coumadin®) and a few anticoagulants used primarily in Europe antagonize the exercise of vitamin Ok and, in flip, prothrombin [8]. For that reason, people who’re taking these anticoagulants want to take care of constant vitamin Ok intakes.
Matrix Gla-protein, a vitamin Ok-dependent protein current in vascular clean muscle, bone, and cartilage, is the main target of appreciable scientific analysis as a result of it’d assist cut back irregular calcification [9]. Osteocalcin is one other vitamin Ok-dependent protein that’s current in bone and could also be concerned in bone mineralization or turnover [5].
Like dietary lipids and different fat-soluble nutritional vitamins, ingested vitamin Ok is integrated into combined micelles through the motion of bile and pancreatic enzymes, and it’s absorbed by enterocytes of the small gut [10]. From there, vitamin Ok is integrated into chylomicrons, secreted into the lymphatic capillaries, transported to the liver, and repackaged into very low-density lipoproteins [2,10]. Vitamin Ok is current within the liver and different physique tissues, together with the mind, coronary heart, pancreas, and bone [2,3,11].
Within the circulation, vitamin Ok is carried primarily in lipoproteins [2]. In comparison with the opposite fat-soluble nutritional vitamins, very small quantities of vitamin Ok flow into within the blood. Vitamin Ok is quickly metabolized and excreted. Based mostly on phylloquinone measurements, the physique retains solely about 30% to 40% of an oral physiological dose, whereas about 20% is excreted within the urine and 40% to 50% within the feces through bile [2,11]. This speedy metabolism accounts for vitamin Ok’s comparatively low blood ranges and tissue shops in comparison with these of the opposite fat-soluble nutritional vitamins [11].
Little is understood concerning the absorption and transport of vitamin Ok produced by intestine micro organism, however analysis signifies that substantial portions of long-chain menaquinones are current within the giant bowel [7]. Though the quantity of vitamin Ok that the physique obtains on this method is unclear, consultants imagine that these menaquinones fulfill a minimum of a number of the physique’s requirement for vitamin Ok [6,7].
Usually, vitamin Ok standing is just not routinely assessed, besides in people who take anticoagulants or have bleeding issues. The one clinically important indicator of vitamin Ok standing is prothrombin time (the time it takes for blood to clot), and unusual modifications in vitamin Ok intakes have hardly ever been proven to change prothrombin time [5]. In wholesome folks, fasting concentrations of phylloquinone in plasma have been reported to vary from 0.29 to 2.64 nmol/L [12]. Nonetheless, it isn’t clear whether or not this measure can be utilized to quantitatively assess vitamin Ok standing. Individuals with plasma phylloquinone concentrations barely under the conventional vary haven’t any scientific indications of vitamin Ok deficiency, probably as a result of plasma phylloquinone concentrations don’t measure the contribution of menaquinones from the food plan and the big bowel [12]. No knowledge on regular ranges of menaquinones can be found [2].
Really useful Intakes
Consumption suggestions for vitamin Ok and different vitamins are supplied within the Dietary Reference Intakes (DRIs) developed by the Meals and Vitamin Board (FNB) on the Institute of Medication of the Nationwide Academies [3]. DRI is the final time period for a set of reference values used for planning and assessing nutrient intakes of wholesome folks. These values, which fluctuate by age and gender, embrace:
Inadequate knowledge have been out there to ascertain an EAR for vitamin Ok, so the FNB established AIs for all ages which are primarily based on vitamin Ok intakes in wholesome inhabitants teams [3]. Desk 1 lists the present AIs for vitamin Ok in micrograms (mcg). The AIs for infants are primarily based on the calculated imply vitamin Ok consumption of wholesome breastfed infants and the belief that infants obtain prophylactic vitamin Ok at start as really helpful by American and Canadian pediatric societies [3].
Sources of Vitamin Ok – “vitamin k in multivitamins”
Meals
Meals sources of phylloquinone embrace greens, particularly inexperienced leafy greens, vegetable oils, and a few fruits. Meat, dairy meals, and eggs include low ranges of phylloquinone however modest quantities of menaquinones [4]. Natto (a standard Japanese meals comprised of fermented soybeans) has excessive quantities of menaquinones [1,13]. Different fermented meals, comparable to cheese, additionally include menaquinones. Nonetheless, the varieties and quantities of vitamin Ok in these meals probably fluctuate relying on the bacterial strains used to make the meals and their fermentation situations [14]. Animals synthesize MK-4 from menadione (an artificial type of vitamin Ok that can be utilized in poultry and swine feed) [15]. Thus, poultry and pork merchandise include MK-4 if menadione is added to the animal feed [1,4,14].
The commonest sources of vitamin Ok within the U.S. food plan are spinach; broccoli; iceberg lettuce; and fat and oils, notably soybean and canola oil [5,7]. Few meals are fortified with vitamin Ok [5]; breakfast cereals are usually not sometimes fortified with vitamin Ok, though some meal substitute shakes and bars are.
Knowledge on the bioavailability of various types of vitamin Ok from meals are very restricted [1]. The absorption fee of phylloquinone in its free type is roughly 80%, however its absorption fee from meals is considerably decrease [2]. Phylloquinone in plant meals is tightly certain to chloroplasts, so it’s much less bioavailable than that from oils or dietary dietary supplements [1]. For instance, the physique absorbs solely 4% to 17% as a lot phylloquinone from spinach as from a pill [2]. Consuming greens similtaneously some fats improves phylloquinone absorption from the greens, however the quantity absorbed continues to be decrease than that from oils. Restricted analysis means that long-chain MKs could have greater absorption charges than phylloquinone from inexperienced greens [7].
A number of meals sources of vitamin Ok are listed in Desk 2. All values on this desk are for phylloquinone content material, besides when in any other case indicated, as a result of meals composition knowledge for menaquinones are restricted [1].
*DV = Every day Worth. The U.S. Meals and Drug Administration (FDA) developed DVs to assist shoppers evaluate the nutrient contents of meals and dietary dietary supplements inside the context of a complete food plan. The DV for vitamin Ok is 120 mcg for adults and kids age 4 years and older [17]. FDA doesn’t require meals labels to record vitamin Ok content material until vitamin Ok has been added to the meals. Meals offering 20% or extra of the DV are thought of to be excessive sources of a nutrient, however meals offering decrease percentages of the DV additionally contribute to a healthful food plan.
The U.S. Division of Agriculture’s (USDA’s) FoodData Central [16] lists the nutrient content material of many meals and supplies complete lists of meals containing vitamin Ok (phylloquinone) organized by nutrient content material and by meals identify, and of meals containing vitamin Ok (MK-4) organized by nutrient content material and meals identify.
Dietary dietary supplements
Vitamin Ok is current in most multivitamin/multimineral dietary supplements, sometimes at values lower than 75% of the DV [18]. Additionally it is out there in dietary dietary supplements containing solely vitamin Ok or vitamin Ok mixed with a number of different vitamins, continuously calcium, magnesium, and/or vitamin D. These dietary supplements are inclined to have a wider vary of vitamin Ok doses than multivitamin/mineral dietary supplements, with some offering 4,050 mcg (5,063% of the DV) or one other very excessive quantity [18].
A number of types of vitamin Ok are utilized in dietary dietary supplements, together with vitamin K1 as phylloquinone or phytonadione (an artificial type of vitamin K1) and vitamin K2 as MK-4 or MK-7 [18]. Few knowledge can be found on the relative bioavailability of the varied types of vitamin Ok dietary supplements. One examine discovered that each phytonadione and MK-7 dietary supplements are effectively absorbed, however MK-7 has an extended half-life [19].
Menadione, which is typically referred to as “vitamin K3,” is one other artificial type of vitamin Ok. It was proven to break hepatic cells in laboratory research carried out throughout the Nineteen Eighties and Nineties, so it’s now not utilized in dietary dietary supplements or fortified meals [3].
Vitamin Ok Intakes and Standing
Most U.S. diets include an satisfactory quantity of vitamin Ok [7]. Knowledge from the 2011–2012 Nationwide Well being and Vitamin Examination Survey (NHANES) present that amongst youngsters and youths aged 2–19 years, the common each day vitamin Ok consumption from meals is 66 mcg [20]. In adults aged 20 and older, the common each day vitamin Ok consumption from meals is 122 mcg for girls and 138 mcg for males. When each meals and dietary supplements are thought of, the common each day vitamin Ok consumption will increase to 164 mcg for girls and 182 mcg for males.
Some analyses of NHANES datasets from 2003–2006 and 2007–2010 raised considerations about common vitamin Ok intakes as a result of solely about one-third of the U.S. inhabitants had a vitamin Ok consumption above the AI [21,22]. The importance of those findings is unclear as a result of the AI is barely an estimate of want, particularly for nutritional vitamins (like vitamin Ok) which are additionally synthesized endogenously. Furthermore, reviews of vitamin Ok deficiency in adults are very uncommon [3,7]. Lastly, meals composition databases present info totally on phylloquinone; menaquinones—both dietary or from bacterial manufacturing within the intestine—probably additionally contribute to vitamin Ok standing [1,6,7].
Vitamin Ok Deficiency
Vitamin Ok deficiency is barely thought of clinically related when prothrombin time will increase considerably attributable to a lower within the prothrombin exercise of blood [3,7]. Thus, bleeding and hemorrhage are the traditional indicators of vitamin Ok deficiency, though these results happen solely in extreme instances. As a result of vitamin Ok is required for the carboxylation of osteocalcin in bone, vitamin Ok deficiency may additionally cut back bone mineralization and contribute to osteoporosis [23].
Vitamin Ok deficiency can happen throughout the first few weeks of infancy attributable to low placental switch of phylloquinone, low clotting issue ranges, and low vitamin Ok content material of breast milk [7]. Clinically important vitamin Ok deficiency in adults could be very uncommon and is often restricted to folks with malabsorption issues or these taking medication that intervene with vitamin Ok metabolism [3,7]. In wholesome folks consuming a various food plan, attaining a vitamin Ok consumption low sufficient to change normal scientific measures of blood coagulation is nearly unattainable [3].