Colorful array of vitamin K rich foods including leafy greens, broccoli, and berries on a white background
Vitamin K is a fat-soluble vitamin essential for several bodily functions. It exists in two primary forms: phylloquinone (vitamin K1), mainly found in green leafy vegetables, and menaquinones (vitamin K2), present in certain animal products and fermented foods, and also produced by gut bacteria. Understanding What Foods Include Vitamin K is crucial for maintaining optimal health.
Vitamin K plays a vital role in synthesizing proteins necessary for blood coagulation and bone mineralization. Prothrombin, a key protein for blood clotting, relies on vitamin K. Osteocalcin, another vitamin K-dependent protein, is essential for building and maintaining healthy bone tissue. This vitamin is stored throughout the body, including the liver, brain, heart, pancreas, and bones. However, it is rapidly metabolized and eliminated from the body, meaning consistent intake through diet is important. Due to its rapid processing, vitamin K toxicity is rare, even with high consumption levels.
Recommended Daily Intake of Vitamin K
The Adequate Intake (AI) level, used when there’s insufficient data for a Recommended Dietary Allowance (RDA), is set to ensure nutritional adequacy. For adults aged 19 and older, the daily AI for vitamin K is 120 micrograms (mcg) for men and 90 mcg for women, including those who are pregnant or breastfeeding.
Health Benefits of Vitamin K Rich Foods
Vitamin K and Blood Clotting
Vitamin K’s most well-known function is its role in blood coagulation. It is necessary for the production of four out of the thirteen proteins involved in the blood clotting process. This process is critical for preventing excessive bleeding from injuries and facilitating wound healing. Individuals on anticoagulant medications (blood thinners) like warfarin, prescribed to prevent blood clots, need to be particularly mindful of their vitamin K intake. These medications work by interfering with vitamin K’s action, and therefore, consistent vitamin K consumption is often advised to maintain stable medication effectiveness. Prothrombin time (PT), a measure of how long blood takes to clot, is used to monitor vitamin K levels and medication effectiveness. While minor dietary fluctuations in vitamin K intake usually have minimal impact on PT, significant and sudden changes can affect PT levels and the efficacy of anticoagulant drugs. Although vitamin K content isn’t mandatory on Nutrition Facts labels, healthcare providers typically educate patients on blood thinners about foods that include vitamin K.
Vitamin K and Bone Health
Beyond blood clotting, vitamin K is essential for bone health. It participates in the synthesis of bone proteins, notably osteocalcin, which is crucial for maintaining strong bones and preventing osteoporosis. Research suggests a correlation between higher vitamin K intake and a reduced risk of hip fractures and improved bone density. Conversely, low vitamin K blood levels have been linked to decreased bone mineral density. The Nurses’ Health Study indicated that women consuming at least 110 mcg of vitamin K daily had a 30% lower risk of hip fractures compared to those with lower intakes. Furthermore, within this study, daily consumption of leafy green vegetables like lettuce was associated with a 50% reduction in hip fracture risk compared to weekly consumption. The Framingham Heart Study also demonstrated a link between high vitamin K intake and a decreased risk of hip fractures in both men and women, along with increased bone mineral density in women. However, studies and meta-analyses on vitamin K supplementation for fracture reduction have yielded mixed results. This inconsistency may stem from the complex nature of bone health, influenced by various factors such as calcium and vitamin D intake, and weight-bearing exercise, potentially overshadowing the benefits of vitamin K supplementation alone.
Vitamin K and Heart Health
Emerging research is exploring vitamin K’s role in cardiovascular health. Vitamin K is involved in the production of matrix Gla proteins (MGP), which help prevent the calcification or hardening of arterial walls, a significant factor in heart disease. By preventing arterial calcification, vitamin K may contribute to maintaining healthy blood vessels and reducing the risk of cardiovascular issues. However, research in this area is still in its early stages, and more studies are needed to determine if vitamin K intake beyond the current recommendations can provide specific benefits for heart health.
What Foods Include Vitamin K? Excellent Food Sources
To ensure adequate vitamin K intake, incorporating foods high in vitamin K into your diet is essential. Here are some of the top food sources:
- Leafy Green Vegetables: These are among the richest sources of vitamin K1. Examples include:
- Kale
- Spinach
- Collard greens
- Turnip greens
- Mustard greens
- Lettuce (especially romaine and green leaf)
- Swiss chard
- Beet greens
- Dandelion greens
- Cruciferous Vegetables: These also provide good amounts of vitamin K:
- Broccoli
- Brussels sprouts
- Cabbage
- Cauliflower
- Certain Fruits: While not as high as leafy greens, some fruits contribute to vitamin K intake:
- Avocado
- Kiwi
- Blueberries
- Grapes
- Figs
- Fermented Foods (Vitamin K2 – Menaquinones):
- Natto (fermented soybeans – exceptionally high in MK-7 form of vitamin K2)
- Sauerkraut
- Kimchi
- Animal Products (Vitamin K2 – Menaquinones):
- Chicken
- Egg yolks
- Cheese (especially hard cheeses)
- Butter
- Plant-Based Oils:
- Soybean oil
- Canola oil
- Olive oil (in smaller amounts)
It’s important to consume a variety of these vitamin K rich foods to meet your daily needs and benefit from the diverse forms of vitamin K.
Signs of Vitamin K Deficiency
Vitamin K deficiency is uncommon in healthy adults but can occur in specific situations. These include individuals taking medications that interfere with vitamin K metabolism, such as antibiotics, or those with conditions causing malabsorption of nutrients. Newborn infants are also at risk due to limited placental transfer of vitamin K and low vitamin K content in breast milk. Infants are often given vitamin K supplements at birth to prevent bleeding risks.
Common signs of vitamin K deficiency include:
- Prolonged blood clotting time or elevated prothrombin time (PT)
- Easy bruising
- Excessive bleeding from wounds, nose, gums, or gastrointestinal tract
- Hemorrhaging
- Osteopenia or osteoporosis (in the long term)
If you suspect a vitamin K deficiency, consult a healthcare professional for proper diagnosis and guidance.
Fun Facts About Vitamin K
- Antibiotics can disrupt vitamin K production by gut bacteria, potentially lowering vitamin K levels, especially with prolonged use. People with poor appetite on long-term antibiotics might benefit from vitamin K supplements.
- As vitamin K is fat-soluble, consuming foods that contain vitamin K with some dietary fat enhances its absorption. Try adding olive oil to your leafy green salads or enjoying avocado with vitamin K-rich meals.
Related Resources
Vitamins and Minerals
References
Last reviewed March 2023
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