Meat, dairy foods, and eggs contain low levels of phylloquinone but modest amounts of menaquinones [ 4 ]. Natto a traditional Japanese food made from fermented soybeans has high amounts of menaquinones [ 1 , 13 ]. Other fermented foods, such as cheese, also contain menaquinones.
However, the forms and amounts of vitamin K in these foods likely vary depending on the bacterial strains used to make the foods and their fermentation conditions [ 14 ]. Animals synthesize MK-4 from menadione a synthetic form of vitamin K that can be used in poultry and swine feed [ 15 ]. Thus, poultry and pork products contain MK-4 if menadione is added to the animal feed [ 1 , 4 , 14 ]. The most common sources of vitamin K in the U. Few foods are fortified with vitamin K [ 5 ]; breakfast cereals are not typically fortified with vitamin K, although some meal replacement shakes and bars are.
Data on the bioavailability of different forms of vitamin K from food are very limited [ 1 ]. Phylloquinone in plant foods is tightly bound to chloroplasts, so it is less bioavailable than that from oils or dietary supplements [ 1 ]. Consuming vegetables at the same time as some fat improves phylloquinone absorption from the vegetables, but the amount absorbed is still lower than that from oils.
Limited research suggests that long-chain MKs may have higher absorption rates than phylloquinone from green vegetables [ 7 ]. Several food sources of vitamin K are listed in Table 2. All values in this table are for phylloquinone content, except when otherwise indicated, because food composition data for menaquinones are limited [ 1 ]. The U. Food and Drug Administration FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet.
The DV for vitamin K is mcg for adults and children age 4 years and older [ 17 ]. FDA does not require food labels to list vitamin K content unless vitamin K has been added to the food. Department of Agriculture's USDA's FoodData Central [ 16 ] lists the nutrient content of many foods and provides comprehensive lists of foods containing vitamin K phylloquinone arranged by nutrient content and by food name , and of foods containing vitamin K MK-4 arranged by nutrient content and food name.
Several forms of vitamin K are used in dietary supplements, including vitamin K1 as phylloquinone or phytonadione a synthetic form of vitamin K1 and vitamin K2 as MK-4 or MK-7 [ 18 ]. Few data are available on the relative bioavailability of the various forms of vitamin K supplements.
One study found that both phytonadione and MK-7 supplements are well absorbed, but MK-7 has a longer half-life [ 19 ]. Menadione, which is sometimes called "vitamin K3," is another synthetic form of vitamin K. It was shown to damage hepatic cells in laboratory studies conducted during the s and s, so it is no longer used in dietary supplements or fortified foods [ 3 ]. Most U. In adults aged 20 and older, the average daily vitamin K intake from foods is mcg for women and mcg for men. When both foods and supplements are considered, the average daily vitamin K intake increases to mcg for women and mcg for men.
The significance of these findings is unclear because the AI is only an estimate of need, especially for vitamins like vitamin K that are also synthesized endogenously. Moreover, reports of vitamin K deficiency in adults are very rare [ 3 , 7 ].
Finally, food composition databases provide information primarily on phylloquinone; menaquinones—either dietary or from bacterial production in the gut—likely also contribute to vitamin K status [ 1 , 6 , 7 ]. Vitamin K deficiency is only considered clinically relevant when prothrombin time increases significantly due to a decrease in the prothrombin activity of blood [ 3 , 7 ].
Thus, bleeding and hemorrhage are the classic signs of vitamin K deficiency, although these effects occur only in severe cases. Because vitamin K is required for the carboxylation of osteocalcin in bone, vitamin K deficiency could also reduce bone mineralization and contribute to osteoporosis [ 23 ]. Vitamin K deficiency can occur during the first few weeks of infancy due to low placental transfer of phylloquinone, low clotting factor levels, and low vitamin K content of breast milk [ 7 ].
Clinically significant vitamin K deficiency in adults is very rare and is usually limited to people with malabsorption disorders or those taking drugs that interfere with vitamin K metabolism [ 3 , 7 ].
In healthy people consuming a varied diet, achieving a vitamin K intake low enough to alter standard clinical measures of blood coagulation is almost impossible [ 3 ]. Vitamin K transport across the placenta is poor, increasing the risk of vitamin K deficiency in newborn babies [ 3 ]. During the first few weeks of life, vitamin K deficiency can cause vitamin K deficiency bleeding VKDB , a condition formerly known as "classic hemorrhagic disease of the newborn.
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 [ 3 , 5 , 23 ].
Vitamin K status can also be low in patients who have undergone bariatric surgery, although clinical signs may not be present [ 26 ]. These individuals might need monitoring of vitamin K status and, in some cases, vitamin K supplementation. This section focuses on two conditions in which vitamin K might play a role: osteoporosis and coronary heart disease. Osteoporosis, a disorder characterized by porous and fragile bones, is a serious public health problem that affects more than 10 million U.
Consuming adequate amounts of calcium and vitamin D, especially throughout childhood, adolescence, and early adulthood, is important to maximize bone mass and reduce the risk of osteoporosis [ 27 ].
The effect of vitamin K intakes and status on bone health and osteoporosis has been a focus of scientific research. Vitamin K is a cofactor for the gamma-carboxylation of many proteins, including osteocalcin, one of the main proteins in bone [ 28 ]. Some research indicates that high serum levels of undercarboxylated osteocalcin are associated with lower bone mineral density [ 5 , 28 ]. Although vitamin K is involved in the carboxylation of osteocalcin, it is unclear whether supplementation with any form of vitamin K reduces the risk of osteoporosis.
In , Cockayne and colleagues conducted a systematic review and meta-analysis of randomized controlled trials that examined the effects of vitamin K supplementation on bone mineral density and bone fracture [ 35 ]. Most of the trials were conducted in Japan and involved postmenopausal women; trial duration ranged from 6 to 36 months. Thirteen trials were included in the systematic review, and 12 showed that supplementation with either phytonadione or MK-4 improved bone mineral density.
Seven of the 13 trials also had fracture data that were combined in a meta-analysis. MK-4 supplementation significantly reduced rates of hip fractures, vertebral fractures, and all nonvertebral fractures.
Other randomized clinical trials since the review by Cockayne et al. In one of these studies, postmenopausal women received either 1 mg phylloquinone, 45 mg MK-4, or placebo daily for 12 months [ 38 ]. All participants also received daily supplements containing mg calcium and IU vitamin D3. At the end of the study, participants receiving either phylloquinone or MK-4 had significantly lower levels of undercarboxylated osteocalcin compared to those receiving placebo.
However, there were no significant differences in bone mineral density of the lumbar spine or proximal femur among any of the treatment groups. In Japan and other parts of Asia, a pharmacological dose of MK-4 45 mg is used as a treatment for osteoporosis [ 5 ]. The European Food Safety Authority has approved a health claim for vitamin K, noting that "a cause and effect relationship has been established between the dietary intake of vitamin K and the maintenance of normal bone" [ 39 ].
Vascular calcification is one of the risk factors for coronary heart disease because it reduces aortic and arterial elasticity [ 40 ]. Matrix Gla-protein MGP is a vitamin K-dependent protein that may play a role in the prevention of vascular calcification [ 5 , 41 ]. Although the full biological function of MGP is unclear, a hypothesis based on animal data suggests that inadequate vitamin K status leads to undercarboxylated MGP, which could increase vascular calcification and the risk of coronary heart disease.
These findings might be particularly relevant for patients with chronic kidney disease because their rates of vascular calcification are much higher than those of the general population [ 9 ]. In an observational study conducted in the Netherlands in postmenopausal women, dietary menaquinone but not phylloquinone intake was inversely associated with coronary calcification [ 42 ].
Menaquinone intake was also inversely associated with severe aortic calcification in a prospective, population-based cohort study involving 4, men and women aged 55 years and older from the Netherlands [ 41 ]. Participants in this study who had dietary menaquinone intakes in the mid tertile Phylloquinone intake had no effect on any outcome. Despite these data, few trials have investigated the effects of vitamin K supplementation on arterial calcification or coronary heart disease risk.
One randomized, double-blind clinical trial examined the effect of phylloquinone supplementation in healthy men and postmenopausal women aged 60—80 years [ 43 ]. Participants received either a multivitamin containing B-vitamins, vitamin C, and vitamin E plus IU vitamin D3, mg calcium, and mcg phylloquinone daily treatment or a multivitamin plus calcium and vitamin D3 only control for 3 years.
There was no significant difference in coronary artery calcification between the treatment and control groups. However, among the participants who adhered to the supplementation protocol, those in the treatment group had significantly less coronary artery calcification progression than those in the control group.
Based on these findings, the authors did not make any clinical recommendations, and they called for larger studies in other populations.
At this time, the role of the different forms of vitamin K on arterial calcification and the risk of coronary heart disease is unclear, but it continues to be an active area of research in the general population and in patients with chronic kidney disease [ 5 , 9 , 44 ]. In its report, the FNB stated that "no adverse effects associated with vitamin K consumption from food or supplements have been reported in humans or animals. Vitamins are essential micronutrients required by the body in small amounts to support a range of vital functions.
Vitamins are divided into two groups: water-soluble B-complex vitamins and C vitamins and fat-soluble vitamins A, D, E and K.
Unlike water-soluble vitamins that need regular replacement in the body, fat-soluble vitamins are stored in the liver and fatty tissues, and are eliminated much more slowly than water-soluble vitamins. For more information on water-soluble vitamins, see fact sheet 9. The fat-soluble vitamins, A, D, E, and K, are stored in the body for long periods of time and generally pose a greater risk for toxicity than water-soluble vitamins when consumed in excess.
Eating a normal, well-balanced diet will not lead to toxicity in otherwise healthy individuals. However, taking vitamin supplements that contain megadoses of vitamins A, D, E and K may lead to toxicity. While diseases caused by a lack of fat-soluble vitamins are rare in the United States, symptoms of mild deficiency can develop without adequate amounts of vitamins in the diet.
Additionally, some health problems, such as inflammatory bowel disease IBD , chronic pancreatitis, and cystic fibrosis, may decrease the absorption of fat, and in turn, decrease the absorption of vitamins A, D, E and K. Consult a medical professional about any potential health problems that may interfere with vitamin absorption. Vitamin A, also called retinol, has many functions in the body.
In addition to helping the eyes adjust to light changes, vitamin A plays an important role in bone growth, tooth development, reproduction, cell division, gene expression, and regulation of the immune system. The skin, eyes, and mucous membranes of the mouth, nose, throat and lungs depend on vitamin A to remain moist. Vitamin A is also an important antioxidant that may play a role in the prevention of certain cancers.
Eating a wide variety of foods is the best way to ensure that the body gets enough vitamin A. The retinol, retinal, and retinoic acid forms of vitamin A are supplied primarily by foods of animal origin such as dairy products, fish and liver. Some foods of plant origin contain the antioxidant, beta-carotene, which the body converts to vitamin A. Beta-carotene, comes from fruits and vegetables, especially those that are orange or dark green in color.
Vitamin A sources also include carrots, pumpkin, winter squash, dark green leafy vegetables and apricots, all of which are rich in betacarotene. The recommendation for vitamin A intake is expressed as micrograms mcg of retinol activity equivalents RAE.
Retinol activity equivalents account for the fact that the body converts only a portion of beta-carotene to retinol. One RAE equals 1 mcg of retinol or 12 mcg of beta-carotene Table 1.
Studies indicate that vitamin A requirements may be increased due to hyperthyroidism, fever, infection, cold, and exposure to excessive amounts of sunlight. Those who consume excess alcohol or have renal disease should also increase intake of vitamin A. Vitamin A deficiency in the United States is rare, but the disease that results is known as xerophthalmia, which can lead to blindness if untreated. It most commonly occurs in developing nations usually due to malnutrition. Since vitamin A is stored in the liver, it may take up to 2 years for signs of deficiency to appear.
Night blindness and very dry, rough skin may indicate a lack of vitamin A. Other signs of possible vitamin A deficiency include decreased resistance to infections, faulty tooth development, and slower bone growth.
Vitamin A deficiency is also a known risk factor for severe measles. According to the World Health Organization WHO , Vitamin A supplementation can significantly reduce mortality rates for children with measles who live in areas with a high prevalence of Vitamin A deficiency. The effectiveness of vitamin A supplementation to treat measles in countries, such as the United States, where vitamin A intakes are generally adequate, is uncertain.
In the United States, toxic or excess levels of vitamin A are more of a concern than deficiencies. It would be difficult to reach this level consuming food alone, but some multivitamin supplements contain high doses of vitamin A.
Retinol is the form of vitamin A that causes the greatest concern for toxicity. If you take a multivitamin, check the label to be sure the majority of vitamin A provided is in the form of beta-carotene, which appears to be safe. Some medications used to treat acne, psoriasis, and other skin conditions contain compounds that mimic retinol in the body. Much like excessive intake of dietary retinol, these medications have been shown to negatively impact bone health and result in delayed growth in children and teens.
Symptoms of vitamin A toxicity include dry, itchy skin, headache, nausea, and loss of appetite. Signs of severe overuse over a short period of time include dizziness, blurred vision and slowed growth. We include products we think are useful for our readers. If you buy through links on this page, we may earn a small commission. Fat-soluble vitamins are vitamins A, D, E, and K. They are present in foods containing fats. The body absorbs these vitamins as it does dietary fats.
They do not dissolve in water. Vitamins help the body function effectively. There are two types: water-soluble and fat-soluble vitamins. The water-soluble vitamins are vitamins B and C. Most vitamins come from food, but sunshine contributes to vitamin D. Some people need or choose to take supplements that provide extra vitamins.
This article looks at the types, functions, and sources of fat-soluble vitamins, and what can happen if a person has too much or too little. Vitamin A helps maintain healthy vision. Without vitamin A, a person could experience vision problems and possibly vision loss. Vitamin A is not a single vitamin but a collection of compounds known as retinoids. Retinoids occur naturally in the human body, and they are present in some dietary sources. Some foods provide retinols, which the body can use directly as vitamin A.
Others provide provitamin A, compounds that the body converts into vitamin A. Learn more here about why we need vitamin A. Plant sources provide carotenoids, such as beta-carotene , which is a powerful antioxidant.
The body can convert these into vitamin A. Find out more here about dietary sources of vitamin A. Food packages usually show the amounts in IU. Anyone who has concerns about their vitamin A intake should seek advice from a health professional, who will help them understand these measures. The — Dietary Guidelines for Americans recommend consuming the following amounts each day. Amounts are in mcg RAE. In severe cases, coma and death can result. Vitamin A supplements are available for purchase online.
However, people should speak to a doctor before taking these or other supplements. The time a person takes a vitamin can affect its impact. Find out more here about when to take different vitamins. People obtain vitamin D :.
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