Vitamin K is a fat-soluble micronutrient known for its crucial role in synthesizing several clotting factors. Vitamin K is also important for healthy bones and preventing and treating osteoporosis. There are three major forms of vitamin K: vitamin K1, also known as phylloquinone, is the natural form found in plants; vitamin K2, also known as menaquinone, is the vitamin K form that is derived from bacteria in the gut; and vitamin K3, also known as menadione, is a synthetic derivative. All three appear to function equally in manufacturing clotting factors, but for other purposes, such as bone strength and health, vitamin K1 appears to be the best. 
The following foods have the highest concentration of vitamin K. For a more expansive list on food sources of specific nutrients visit Health Canada's Dietary Reference Intakes for Vitamins or USDA's National Nutrient Database
Other food sources include:
The following are the primary uses of Vitamin K. 
- Osteoporosis: Vitamin K plays a role in converting osteocalcin, a non-collagen protein found in the bone, into its active form. Osteocalcin, once activated, serves to anchor calcium into place within the bone. As may be predicted based on this role, when vitamin K1 is deficient, it can lead to impaired mineralization of the bone due to diminished functioning of osteocalcin. Osteoporosis increases ones risk of fracture. It has been shown that the greater the deficiency in vitamin K, the greater the severity of the fracture.
- Excessive menstrual bleeding: Even if vitamin K levels appear to be normal, the use of vitamin K may help in the treatment.
- Hemorrhagic disease of the newborn: Newborns are born with a sterile intestinal tract, meaning that they are not capable of synthesizing vitamin K2, the form of vitamin K that is produced by gut bacteria. Since 1961, the Committee on Nutrition of the American Academy of Pediatrics has recommended that all newborns be injected with vitamin K1 in order to prevent early vitamin K deficiency bleeding. Oral doses have also been used.
Deficiency symptoms are rare as the gut bacteria produce vitamin K2. Typically when deficiency is present, it is a result of anticoagulant therapy. Symptoms may include:
- easy bruising
- appearance of ruptured capillaries
Naturally occurring vitamin K1 is generally considered non-toxic, whereas the synthetic derivative, vitamin K3, has been associated with potentially severe toxicity reactions at high doses. These symptoms may include:
- flushing and perspiration
- difficulty breathing
- tightness in throat or chest
- chest pain
- hives, rash, or itchy or swollen skin
- rarely hemolytic anemia
Common Deficiency Tests: 
- Plasma Prothrombin - a high level indicates a deficiency
- Serum Vitamin K - - a low level indicates a deficiency
- Vitamin K1 (phylloquinone) appears to be the best form. One of the best sources is fat-soluble chlorophyll. Most of the chlorophyll in food supplements at health food stores is water-soluble.
- Water-soluble chlorophyll is, however, an excellent healer and astringent and can be used topically for skin wounds.
- Some advantages of the fat-soluble form over the water-soluble form are that the fat-soluble form can stimulate hemoglobin and red blood cell production and can relieve excessive menstrual blood flow. It also contains beta-carotene, and antioxidant and anti-cancer activity 
- The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- Infants: 5mg (under 6 months); 10mg (6-12 months)
- Child: 15mg (1-3 years); 20mg (4-6 years); 30mg (7-10 years)
- Adolescent: 45mg (Males and Females 11-14 years); 65mg (Males 15-18 years); 55mg (Females 15-18 years)
- Adult: 70mg (Males 19-24 years); 60mg (Females 19-24 years); 80mg (Males 25+ years); 65mg (Females 25+ years)
- Pregnancy and Lactation: 65mg
- Children: Vitamin K can cause a fatal form of jaundice in infants. No adverse effects have been reported among breast-fed infants. Large doses of menadione may produce hemolyticanemia, hyperbilirubinemia, and kernicterus in infants.
- Adults: generally regarded as safe
- Seniors: generally regarded as safe
- Pregnancy and Breastfeeding: No extant reports of adverse effects have been related to fetal development during pregnancy. Vitamin K crosses the placenta and is excreted into breast milk.
- Contraindications: Patients undergoing anti-vitamin K anticoagulant therapy, except within the context of appropriate professional supervision (monitor INR and titrate dose of vitamin K regularly); some premature infants.
- General adverse effects: rare reports of cutaneous allergic reaction to intramuscular vitamin K1; less than 1% have reported abnormal taste, anaphylaxis, cyanosis, diaphoresis, dizziness, dyspnea, GI upset from oral doses, hemolysis in neonates and in individuals with glucose-6-phosphate dehydrogenase deficiency, hypersensitivity reactions, hypotension, pain, tenderness at injection site, transient flushing reaction, potential risk of cirrhosis with supplemental intake
- Drug Interactions include:
- Addresses Drug-Induced Deficiency:
- Antibiotics - Drug can inhibit or eliminate beneficial intestinal flora, thus disrupting gut ecology and interfering with endogenous vitamin K2 synthesis. Cephalosporins also disrupt synthesis of active clotting factors by inhibiting hepatic vitamin K epoxide reductase. Administer vitamin K and follow with probiotics. Monitor INR when necessary.
- Bile Acid Sequestrants - Drug interferes with absorption of vitamin K and other fat-solube nutrients.
- Corticosteroids, oral, Including Prednisone - Drug can cause increased urinary loss of vitamin K as well as depletion of other key nutrients. Long-term drug use may lead to clinically significant depletion, particularly affecting bone mass.
- Phenytoing, Phenobarbital, and Related Anticonvulsant Medications - Many anticonvulsants increase breakdown of vitamin K by inducing hepatic enzymes. Greatest significance is during pregnancy. Co-administer vitamin K especially during pregnancy.
- MIneral Oil - Mineral oil may interfere with absorption of vitamin K and other nutrients. Malabsorption of vitamin K can increase anticoagulant activity of warfarin. Separate intake is recommended.
- Warfarin and Related Oral Vitamin K Antagonist Anticoagulants - Drugs act by inhibiting conversion of the vitamin K epoxide back to vitamin K. Excessive vitamin K intake, directly or within foods or herbs, will interfere with therapeutic action, unless closely monitored, dose-titrated, and properly managed within comprehensive therapeutic strategy. Adverse effects can be rapid and severe. Limit and tightly regulate vitamin K intake. Closely monitor INR and titrate drug at close intervals when administering herbs, nutrients, or foods with substantial vitamin K content.
- Nutrient Interactions include:
- Vitamin C - Co-adminstration of menadione bisulfite and ascorbate has been shown to provide relief of nausea and vomiting of pregnancy within 3 days. Also, vitamin K2 combined with IV ascorbate has shown recent promise as an oxidative therapy for cancer.
- Vitamin E - Vitamin E in high doses may interfere with the absorption and utilization of vitamin K. This may play a role in cases of enhanced anticoagulant effect in response to high-dose vitamin E intake reported among individuals taking oral anticoagulants.
- Murray Michael T (2005) Encyclopedia of Nutritional Supplements, The Essential Guide for Improving Your Health Naturally, Prima Publishing
- Medlineplus 
- Bralley J Alexander and Lord Richard S (2005) Laboratory Evaluations in Molecular Medicine, Nutrients, Toxicants, and Cell Regulators Institute for Advances in Molecular Medince, GA
- Stargrove Mitchell Bebell, Treasure Jonathan, McKee Dwight L 2008 Herb, Nutrient, and Drug Interactions, Clinical Implications and Therapeutic Strategies. Mosby