Vitamin K is actually a family of compounds made up of K1 (phylloquinone) and K2 (menaquinones, further classified into MK4-13). It’s a critical cofactor in blood clotting and maintains normal calcification (ie. in bones and teeth and not in soft tissues and blood vessels). It’s found in leafy green veggies and fermented foods. Some types of bacteria in our gut actually produce K2 as well but based on the latest research it is unclear if we’re able to absorb the vitamin K from our digestive tract.

Food sources

K1

Dark leafy greens like chard, turnip greens, kale, spinach, broccoli

K2

Fermented foods like natto, kimchi, sauerkraut, kefir, yogurt

Deficiency

Severe deficiency results in bleeding/hemorrhage. This is most common in newborn infants, especially those exclusively breastfed, because there is low transmission of Vitamin K across the placenta and in breast milk.

People with malabsorption syndromes and other gastrointestinal disorders, such as cystic fibrosis, celiac disease, ulcerative colitis, and short bowel syndrome, as well as those who’ve had bariatric surgery, are also at risk of deficiency.

Insufficiency is very common, especially in older adults. It increases the risk of osteoporosis, heart disease and other diseases related to blood vessel calcification (like certain types of hypertension, stroke, and cognitive decline).

Supplementation

Adults

I recommend all adults take K2 with their D3. MK-7 is the best-absorbed form. Dosage will vary depending on D3 dose when taking in combination. There are no established upper limits for intake because of its low potential for toxicity.

Infants

The American Academy of Pediatrics recommends a single intramuscular dose of 0.5-1 mg Vitamin K1 at birth to prevent vitamin K deficiency bleeding (VKDB). Some brands may contain aluminum, so I recommend checking with your hospital ahead of time. For families who choose not to receive this injection, studies suggest that oral dosage of vitamin K is sufficient to prevent VKDB in healthy newborns. Your functional medicine doctor can provide you with a specific dosing regimen.

Children

There is no established supplementation recommendation during childhood. Studies are limited to children with cystic fibrosis and though they suggest that supplementation is helpful for normal bone development, a specific dose hasn’t been determined.

Talk with your functional medicine doctor to determine the best dose for you based on your risk factors, genetic factors, and diet. As always, check with your pediatrician and/or functional medicine doctor first before starting any supplement to make sure it’s right for you or your child.

To see my favorite supplements, check out my Fullscript dispensary.

PMID: 11220402, 18982351