Vitamin K Guide

What is Vitamin K?

Vitamin K is a fat-soluble vitamin that plays a crucial role in blood clotting, bone metabolism, and regulating blood calcium levels. The "K" comes from the German word "koagulation," reflecting the vitamin's essential role in coagulation (blood clotting).

Forms of Vitamin K

Vitamin K exists in several forms:

Vitamin K1 (phylloquinone): Found primarily in green leafy vegetables and the primary dietary form.
Vitamin K2 (menaquinones): A group of compounds (MK-4 through MK-13) produced by bacteria in the intestinal tract and found in fermented foods and animal products. MK-7 is the most well-studied form.
Vitamin K3 (menadione): A synthetic form that is no longer used in human supplements but may be used in animal feed.

Recommended Daily Intake

The recommended daily allowance (RDA) for vitamin K:

Infants (0-12 months): 2-2.5 mcg
Children (1-13 years): 30-60 mcg
Adolescents (14-18 years): 75 mcg
Adult men (19+ years): 120 mcg
Adult women (19+ years): 90 mcg
Pregnant/breastfeeding women: 90 mcg

Note: These values refer primarily to vitamin K1. There is currently no separate recommendation for vitamin K2.

Key Benefits

Essential for blood clotting and preventing excessive bleeding
Supports bone health by activating proteins that bind calcium to bones
May help prevent vascular calcification (hardening of arteries)
Regulates cell growth and may have anti-cancer properties
Plays a role in cognitive health and brain function
May help improve insulin sensitivity
Supports heart health, especially vitamin K2
Involved in energy metabolism

Deficiency Symptoms

Vitamin K deficiency is relatively rare in adults but more common in newborns. Symptoms and signs include:

Easy bruising and excessive bleeding from wounds, punctures, and injections
Nosebleeds
Bleeding gums
Blood in urine or stool
Heavy menstrual periods
In severe cases, internal bleeding that can be life-threatening
Poor bone development or increased fracture risk (long-term deficiency)

Risk Factors for Deficiency

Certain conditions increase the risk of vitamin K deficiency:

Newborn infants (naturally low levels at birth)
Malabsorption disorders (Crohn's, celiac disease, cystic fibrosis)
Long-term antibiotic use (reduces gut bacteria that produce vitamin K2)
Liver disease or disorders affecting fat absorption
Use of anticoagulant medications like warfarin (which work by inhibiting vitamin K)
Severe malnutrition

Food Sources

Dark Leafy Greens:
- Kale, raw (1 cup): 113 mcg (94% DV)
- Collard greens (1 cup): 640 mcg (533% DV)
- Spinach (1 cup): 145 mcg (121% DV)
- Swiss chard (1 cup): 299 mcg (249% DV)
- Mustard greens (1 cup): 278 mcg (232% DV)
Cruciferous Vegetables:
- Brussels sprouts (1 cup): 156 mcg (130% DV)
- Broccoli (1 cup): 110 mcg (92% DV)
- Cabbage (1 cup): 67.6 mcg (56% DV)
- Cauliflower (1 cup): 16.6 mcg (14% DV)
Herbs and Spices:
- Parsley (1/4 cup): 246 mcg (205% DV)
- Cilantro (1/4 cup): 12.4 mcg (10% DV)
- Sage (1 tbsp): 34.3 mcg (29% DV)
- Thyme (1 tbsp): 28.1 mcg (23% DV)
Vegetables:
- Green peas (1 cup): 41.4 mcg (35% DV)
- Cucumber with peel (1 cup): 17.1 mcg (14% DV)
- Celery (1 cup): 29.6 mcg (25% DV)
- Asparagus (1 cup): 41.6 mcg (35% DV)
- Green beans (1 cup): 14.4 mcg (12% DV)
Fermented Foods:
- Natto (100g): 939 mcg (783% DV)
- Sauerkraut (1 cup): 18.6 mcg (16% DV)
- Kimchi (1 cup): 65 mcg (54% DV)
Oils:
- Soybean oil (1 tbsp): 25 mcg (21% DV)
- Olive oil (1 tbsp): 8.4 mcg (7% DV)
- Canola oil (1 tbsp): 10.4 mcg (9% DV)
Other Sources:
- Pine nuts (1 oz): 15.3 mcg (13% DV)
- Blueberries (1 cup): 28.5 mcg (24% DV)
- Grapes (1 cup): 22.1 mcg (18% DV)
- Pomegranate (1 whole): 14.3 mcg (12% DV)

Note: DV = Daily Value (120 mcg for adults). Values are approximate and may vary based on growing conditions and preparation methods.

Absorption Factors

Several factors affect vitamin K absorption:

Requires dietary fat for proper absorption
Bile acids are essential for absorption
About 10-15% of vitamin K1 from food is absorbed
Vitamin K2 is more bioavailable than K1
Long-term antibiotic use can reduce production of K2 by gut bacteria

Important: If you're taking blood thinners like warfarin (Coumadin), maintain a consistent intake of vitamin K-rich foods. Sudden changes can interfere with medication effectiveness.

Supplement Information

Vitamin K supplements are available in several forms:

Vitamin K1 (phylloquinone)
Vitamin K2 as MK-4 (short-chain menaquinone)
Vitamin K2 as MK-7 (long-chain menaquinone with better bioavailability)
Combination supplements with vitamin D and calcium

Note: There is no established upper limit for vitamin K intake. However, supplementation should be avoided or done under medical supervision if you're taking warfarin or other vitamin K antagonists.

Special Considerations

Vitamin K for Newborns

Newborns have low vitamin K levels because this vitamin doesn't cross the placenta efficiently, and their intestines haven't yet developed bacteria that produce vitamin K. For this reason, a vitamin K injection is routinely given to newborns to prevent vitamin K deficiency bleeding (VKDB), a rare but serious condition that can cause brain damage or death.

Vitamin K and Bone Health

Both K1 and K2 activate osteocalcin, a protein that binds calcium to bone matrix. Some research suggests that vitamin K2 (particularly MK-7) may be more effective for bone health than K1. Adequate vitamin K intake is associated with higher bone mineral density and reduced fracture risk, especially when combined with adequate vitamin D and calcium.

Vitamin K and Warfarin

If you take warfarin (Coumadin) or other vitamin K antagonists, it's important to maintain a consistent intake of vitamin K. Sudden changes in vitamin K consumption can affect INR (blood clotting time) and either increase bleeding risk or reduce the medication's effectiveness. Work with your healthcare provider to establish a consistent vitamin K intake rather than avoiding vitamin K-rich foods entirely.

Take Our Vitamin Test

Concerned about a possible vitamin K deficiency? Our comprehensive vitamin deficiency test can help identify potential nutritional gaps based on your symptoms.

Back to Vitamin Guide Ask a Question