Vitamin K and Leafy Greens

Leafy greens are everywhere on the Korean table: blanched and dressed as namul, wrapped around rice and meat as ssam, pickled in soy sauce, and folded into kimchi. Among the nutrients they supply, vitamin K stands out, and several Korean greens are among the richest sources in any cuisine. For most people that is simply good news. For people taking the blood thinner warfarin, it is a reason to pay attention to how much they eat from week to week.

What vitamin K does

MedlinePlus describes vitamin K as a fat-soluble vitamin needed for blood clotting and for healthy bones. The adequate intake for adults is 120 micrograms (µg) a day for men and 90 µg for women, including during pregnancy and breastfeeding. Green leafy vegetables are the main dietary source; cabbage-family vegetables supply some, and smaller amounts come from fish, meat and eggs. Bacteria in the gut also make vitamin K.

Korean greens by the numbers

The Korean Food Composition Table, published by the National Institute of Agricultural Sciences, lists these approximate vitamin K values per 100 g:

• Perilla leaf (kkaennip): about 787 µg raw and 656 µg blanched, the highest of the greens here.
• Spinach: about 390 µg raw and 431 µg blanched.
• Dureup (angelica tree shoots): about 386 µg blanched.
• Crown daisy (ssukgat): about 191 µg raw and 311 µg blanched.
• Leaf lettuce (sangchu): about 237 µg raw.
• Shepherd's purse (naengi): about 224 µg blanched.
• Water dropwort (minari): about 203 µg blanched.
• Rough aster (chamchwi): about 150 µg blanched.
• Napa cabbage and kimchi: about 74 µg for raw cabbage and 70 µg for cabbage kimchi.

Blanched figures are often higher than raw ones because cooking drives out water, concentrating what remains in each gram.

How banchan portions fit in

A banchan serving is small, but these greens are dense. As a rough illustration, 50 g of blanched spinach in sigeumchi-namul would supply about 215 µg, and a few perilla leaves add up quickly when eaten as kkaennip-namul, as kkaennip-jangajji or as wraps at a barbecue. A meal with ssukgat-muchim, minari-muchim, naengi-muchim and a lettuce ssam platter could easily provide several times the adequate intake.

Seasonal eating adds variation. Spring brings wild greens such as dureup, naengi and chamnamul to the table in quantity, while winter tables may lean more on kimchi and root vegetables. See seasonal foods and vegetables and namul.

Vitamin K and warfarin

MedlinePlus explains that vitamin K and foods containing it can affect how warfarin works, so a sudden rise or fall in intake matters. MedlinePlus does not tell people on warfarin to avoid leafy greens. Its advice is to keep the amount of vitamin K foods steady from day to day and week to week, to avoid suddenly eating large amounts of leafy greens or certain vegetable oils, and to talk with a doctor before making big changes to the diet. It also advises checking with a provider before starting vitamins, supplements or other medicines, and asking about alcohol.

For a Korean-style diet, that consistency might look like this:

• Keep a usual pattern: If namul is part of most days, keep it part of most days rather than eating none for a week and a large platter at the weekend.
• Plan for feasts and seasons: Holiday spreads, spring foraging and barbecue nights with piles of lettuce and perilla can mean a sudden jump. Mention big changes to the care team.
• Know the heavy hitters: Perilla leaves and spinach are the most concentrated in the list above; cabbage kimchi is much lower per bite.
• Watch supplements and green powders: Concentrated green products and multivitamins can contain vitamin K too.

This guidance concerns warfarin. Other anticoagulants work differently, so ask a pharmacist or doctor what applies to your own medicine. Anyone on blood thinners should follow the advice of their prescriber rather than this general overview.