Vitamin K and Its Role in Health

Vitamin K Fact Sheet

• Vitamin K is a fat-soluble vitamin naturally found in foods and supplements.
• It includes phylloquinone (vitamin K1) and menaquinones (vitamin K2).
• Menaquinones (MK-4, MK-7, MK-9) have unsaturated isoprenyl side chains.
• Phylloquinone is primarily in green leafy vegetables and is the main dietary form.
• Menaquinones are mostly bacterial and present in small amounts in animal and fermented foods.
• The human gut produces most menaquinones, particularly long-chain ones.
• Vitamin K is a coenzyme for vitamin K-dependent carboxylase.
• This enzyme is critical for blood clotting and bone metabolism.
• Prothrombin (clotting factor II) is a vitamin K-dependent plasma protein involved in clotting.
• Warfarin and some anticoagulants counteract vitamin K's activity and prothrombin, affecting individuals on anticoagulant therapy.
• Matrix Gla-protein (MGP) and osteocalcin are vitamin K-dependent proteins associated with reducing abnormal calcification and bone formation respectively.
• Ingested vitamin K is absorbed in the small intestine, like other fat-soluble vitamins.
• It's incorporated into chylomicrons and transported to the liver by lymphatic capillaries.
• Vitamin K is found in various body tissues, including liver, brain, heart, pancreas, and bone.
• Circulating vitamin K is primarily in lipoproteins. Amounts are very small compared to other fat-soluble vitamins.
• Vitamin K is rapidly metabolised and excreted through urine and feces (bile).

Recommended Intakes

• Adequate Intakes (Als) are the reference for estimating healthy individual needs.
• Als vary by age and gender and are listed in micrograms (mcg).
• Als for infants are based on breastfed infant intakes and birth prophylaxis recommendations.
• Dietary Reference Intakes (DRIs) are reference values for planning and assessing nutrient intakes.

Sources of Vitamin K

• Good sources include spinach, broccoli, iceberg lettuce, and vegetable oils (soybean, canola).
• Natto (fermented soybeans) has high menaquinones.
• Other fermented foods and meats contain menaquinones.
• Vitamin K bioavailability from foods is generally lower than supplements.
• Absorption is dependent on consuming foods with fat.
• Table 2 lists foods and their phylloquinone content.

Dietary Supplements

• Most multivitamin/mineral supplements include vitamin K, usually less than the Daily Value (DV).
• Supplements are also available containing only vitamin K.
• Phylloquinone and menaquinones (MK-4 and MK-7) are common supplement forms.
• Menadione (vitamin K3) is a synthetic form no longer used in supplements. Evidence indicated damage to hepatic cells.

Vitamin K Intake & Status

• Most U.S. diets contain adequate vitamin K.
• Average intakes from foods are 66 mcg in 2-19-year-olds and 122-138 mcg in older adults.
• Intake increases to 164-182 mcg when supplements are included.

Vitamin K Deficiency

• Deficiency is clinically relevant mainly when prothrombin time is affected by low prothrombin activity.
• Bleeding and hemorrhage are the main signs but are only seen in severe cases.
• Low vitamin K may impact bone mineralization potentially impacting bone health.
• Infants are susceptible due to low placental transfer, low clotting factors, or low content in breast milk.
• Deficiency is rare in adults consuming a varied diet.

Groups at Risk

• Newborns not receiving vitamin K at birth are at increased risk for bleeding.
• Those with malabsorption disorders may not absorb vitamin K properly, and bariatric surgery patients may also have low vitamin K.

Vitamin K and Health

• This section focuses on osteoporosis and coronary heart disease.
• Osteoporosis is a condition of fragile bones and vitamin K is important for bone health.
• Some research suggests a link between vitamin K and increased bone density/ decreased hip fractures.
• Vitamin K supplementation may improve bone strength in post-menopausal women.
• Vascular calcification is a risk factor for coronary heart disease and MGP may prevent it.
• Low vitamin K intake may be linked to coronary heart disease mortality.
• Research is ongoing on the role of vitamin K in arterial calcification.

Health Risks from Excessive Vitamin K

• According to the FNB, no toxicity concerns exist based on the available data from humans and animals.

Interactions with Medications

• Vitamin K interacts with anticoagulants (warfarin, Coumadin, and others).
• Antibiotics may decrease vitamin K status, potentially more so with cephalosporins, affecting the gut bacteria.
• Bile acid sequestrants and orlistat can decrease vitamin K absorption.
• Consistent monitoring may be necessary for those taking these medications.

This quiz explores the essential functions of Vitamin K in the body, including its dietary sources and potential deficiencies. Test your knowledge on how Vitamin K interacts with medications and the benefits of maintaining adequate levels.