What is the difference between vitamin K1 and K2?

Vitamin K1 and vitamin K2 are two kinds of the same vitamin. Both are built on the same ring, and they differ in the side chain attached to that ring and in where they come from. Vitamin K1 is phylloquinone, made by plants and found mainly in green leaves and some plant oils. Vitamin K2 is a group of compounds called menaquinones, named MK-4 to MK-13 by the length of their side chain, which are mostly made by bacteria and are found in natto, cheese and, in smaller amounts, animal foods. The Thai Reference Daily Intake (Thai RDI) for vitamin K is 60 µg a day.

In short:

• Same ring, different tail: K1 has one fixed side chain; K2 side chains have 4 to 13 repeating units
• K1 comes from: green leafy vegetables and plant oils such as soybean oil
• K2 comes from: bacteria, fermented foods (natto MK-7, cheese) and animal foods (MK-4)
• Thai foods: amaranth leaves, garland chrysanthemum, coriander and sweet potato leaves are high in K1
• Daily amount: Thai RDI 60 µg (one value for vitamin K)

This article compares the two by structure, origin and the amounts found in food. For the daily amounts of other nutrients, see What are the Thai daily reference amounts for each nutrient?

What are vitamin K1 and vitamin K2?

The NIH Office of Dietary Supplements (ODS), part of the US National Institutes of Health, describes vitamin K as the generic name for a family of compounds that share the chemical structure 2-methyl-1,4-naphthoquinone. It is a fat-soluble vitamin. The family includes phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2).

The shared ring

The common part is a double ring called a naphthoquinone, with a methyl group attached. On its own, without a side chain, this ring is menadione, which PubChem lists as 2-methylnaphthalene-1,4-dione (C11H8O2). Menadione is a synthetic form; the ODS notes that it can be used in poultry and pig feed.

The side chain makes the difference

Vitamin K1 and the K2 menaquinones all carry a long side chain on the ring. In K1 the chain is mostly saturated, with one double bond. In menaquinones the chain is made of repeating unsaturated units called isoprenyl units, and the number of units gives each menaquinone its name: MK-4 has four, MK-7 has seven. The ODS says MK-4, MK-7 and MK-9 are the most studied menaquinones.

K1 and MK-4 have a similar number of carbon atoms (31), but MK-4 has six fewer hydrogen atoms because of the extra double bonds in its chain. MK-7 is much longer, with 46 carbon atoms.

Where does each form come from?

Vitamin K1 comes from plants

Phylloquinone is made by plants. The ODS says it is present mainly in green leafy vegetables and is the main form of vitamin K in the diet, and that in plant foods it is tightly bound to the chloroplasts, the parts of plant cells where photosynthesis happens. Plant oils such as soybean, canola and olive oil also contain it.

Vitamin K2 comes mostly from bacteria

The ODS says menaquinones are mainly of bacterial origin and are present in modest amounts in various animal-based and fermented foods. Almost all menaquinones, especially the long-chain ones, are also made by bacteria in the human gut. The forms and amounts in a fermented food likely vary with the bacterial strains used and the fermentation conditions. The 2007 study from Kobe Pharmaceutical University in Japan, which measured 58 foods, found MK-4 spread widely through animal foods and MK-7 characteristically in fermented soybean products such as natto.

MK-4 is the exception

MK-4 is not mainly made by bacteria. The ODS says the body makes MK-4 from phylloquinone through a conversion that does not involve bacteria, and that animals make MK-4 from menadione, so poultry and pork contain MK-4 when menadione is added to the feed. A 2014 review from Guy's and St Thomas' NHS Foundation Trust in London describes a human enzyme, UBIAD1, that takes part in converting phylloquinone to MK-4, and recent studies suggesting that the side chain of phylloquinone taken by mouth is removed in the intestine, with menadione circulating as a starting material for MK-4 in tissues.

Which foods have the most vitamin K1?

Vitamin K1 per 100 g of vegetables and fruit

The figures below come from the US Department of Agriculture's FoodData Central database (SR Legacy), per 100 g of raw food, with each compared with the Thai RDI of 60 µg. Thai varieties may give somewhat different amounts.

Herbs such as parsley, basil and coriander are high per 100 g but are usually eaten in small amounts. A 2007 study from Kobe Pharmaceutical University in Japan measured 58 foods and found phylloquinone widely in green vegetables and algae, with 498 µg per 100 g in raw spinach and 307 µg in raw broccoli. Its broccoli figure is about three times the US one, which shows how much the same vegetable can vary between samples.

Vitamin K1 in cooking oils

The oils most used in Thai cooking differ widely: soybean oil has many times more K1 than palm oil, and coconut oil has almost none.

Which foods contain vitamin K2?

Food data on menaquinones are more limited than for phylloquinone. The ODS says this is why most food tables list only K1.

Natto, cheese and dairy

The Kobe study found MK-7 characteristically in fermented soybean products such as natto, while MK-4 was spread widely through animal foods at lower levels than K1. A 2017 study from the USDA Human Nutrition Research Center on Aging at Tufts University measured K1 and MK-4 to MK-13 in US milk, yoghurt, cream and cheese. Full-fat dairy foods contained appreciable menaquinones, mainly MK-9, MK-10 and MK-11, with little MK-5 to MK-7. Reduced-fat or fat-free products had about 5 to 22% of the vitamin K of their full-fat versions, so the vitamin K in dairy rose with the fat content.

Thai fermented soybeans

Northern Thailand has its own fermented soybeans, such as thua nao. A 2023 study from Chiang Mai University found that bacteria of the genus Bacillus made up 49.5 to 86.8% of the bacteria in fermented soybeans made by Karen, Lawa and Shan communities. The study looked at bacteria, not at vitamin K, so the menaquinone content of Thai fermented soybeans is not known from it.

How much vitamin K is in a usual serving?

The ODS lists vitamin K per typical US serving, based on FoodData Central. Values are K1 unless marked otherwise. The last column compares each serving with the Thai RDI of 60 µg.

Source: ODS vitamin K fact sheet, Table 2 (US servings). The share of 60 µg is our comparison with the Thai RDI and only shows the size of each figure.

Why the two tables look different

A raw cup of spinach weighs much less than 100 g, so its 145 µg per cup is lower than the 482.9 µg per 100 g. A tablespoon of oil is small too, so oils give less per serving than their 100 g figures suggest.

How much vitamin K do you need a day, and is there an upper limit?

The Thai RDI for vitamin K is 60 µg a day, for the general population aged 3 and over. It is one value for vitamin K as a whole and does not split K1 and K2. The UK's NHS says you should be able to get all the vitamin K you need from a varied and balanced diet, and that vitamin K not needed straight away is stored in the liver, so it is not needed every day.

How much people eat, and in which forms

The Kobe study estimated the vitamin K intake of young women in eastern Japan at about 230 µg a day. Of this, 67.7% was phylloquinone, 24.9% MK-7 and 7.3% MK-4, with vegetables and algae and fermented soybean foods as the main contributors. The study covered one group in one region, and similar data for Thailand were not found.

Upper limits

Who should talk to a doctor or pharmacist?

People who take regular medication

Vitamin K interacts with some medicines, and some medicines can affect vitamin K levels in the body. If you take medication regularly, talk to a doctor or pharmacist before taking supplements that contain vitamin K.

Pregnant and breastfeeding women

If you are pregnant or breastfeeding, talk to a doctor or pharmacist before taking any dietary supplement, including vitamin K.

Dietary supplements are not intended to prevent, treat or cure any disease.