Determination of phylloquinone and menaquinones in food. Effect of food matrix on circulating vitamin K concentrations

Abstract

Fluctuations in international normalized ratio values are often ascribed to dietary changes in vitamin K intake. Here we present a database with vitamin K(1) and K(2) contents of a wide variety of food items. K(1) was mainly present in green vegetables and plant margarins, K(2) in meat, liver, butter, egg yolk, natto, cheese and curd cheese. To investigate the effect of the food matrix on vitamin K bioavailability, 6 healthy male volunteers consumed either a detergent-solubilized K(1) (3.5 micromol) or a meal consisting 400 g of spinach (3.5 micromol K(1)) and 200 g of natto (3.1 micromol K(2)). The absorption of pure K(1) was faster than that of food-bound K vitamins (serum peak values at 4 h vs. 6 h after ingestion). Moreover, circulating K(2) concentrations after the consumption of natto were about 10 times higher than those of K(1) after eating spinach. It is concluded that the contribution of K(2) vitamins (menaquinones) to the human vitamin K status is presently underestimated, and that their potential interference with oral anticoagulant treatment needs to be investigated.

Full text

Original Paper
Haemostasis 2000;30:298–307
Determination of Phylloquinone and
Menaquinones in Food
Effect of Food Matrix on Circulating Vitamin K Concentrations
Leon J. Schurgers Cees Vermeer
Department of Biochemistry and Cardiovascular Research Institute, Maastricht University,
Maastricht, The Netherlands
Received: July 27, 2000
Accepted in revised form: September 27, 2000
Cees Vermeer, PhD
Department of Biochemistry, University of Maastricht
PO Box 616, NL–6200 MD Maastricht (The Netherlands)
Tel. +31 43 388 1682, Fax +31 43 388 4160
E-Mail c.vermeer@bioch.unimaas.nl
ABC
Fax +41 61 306 12 34
E-Mail karger@karger.ch
www.karger.com
© 2001 S. Karger AG, Basel
0301–0147/00/0306–0298$17.50/0
Accessible online at:
www.karger.com/journals/hae
Key Words
Phylloquinone W Menaquinone W Vitamin K W
Food composition W Bioavailability W
Anticoagulant, oral
Abstract
Fluctuations in international normalized ratio
values are often ascribed to dietary changes
in vitamin K intake. Here we present a data-
base with vitamin K1 and K2 contents of a
wide variety of food items. K1 was mainly
present in green vegetables and plant mar-
garins, K2 in meat, liver, butter, egg yolk, nat-
to, cheese and curd cheese. To investigate
the effect of the food matrix on vitamin K
bioavailability, 6 healthy male volunteers
consumed either a detergent-solubilized K1
(3.5 Ìmol) or a meal consisting 400 g of
spinach (3.5 Ìmol K1) and 200 g of natto
(3.1 Ìmol K2). The absorption of pure K1 was
faster than that of food-bound K vitamins (se-
rum peak values at 4 h vs. 6 h after ingestion).
Moreover, circulating K2 concentrations after
the consumption of natto were about 10
times higher than those of K1 after eating spi-
nach. It is concluded that the contribution of
K2 vitamins (menaquinones) to the human
vitamin K status is presently underestimated,
and that their potential interference with oral
anticoagulant treatment needs to be investi-
gated.
Copyright © 2001 S. Karger AG, Basel
Introduction
Vitamin K is an essential dietary micronu-
trient that facilitates the synthesis of specific
blood coagulation factors and of proteins in-
volved in bone metabolism and vascular biol-
ogy [1, 2]. It serves as a cofactor for the mem-
brane-bound microsomal enzyme Á-glutamyl-
carboxylase [3]. Dietary vitamin K is ab-
sorbed and transported in blood in its most
stable form, i.e. as a quinone. Vitamin K
occurs in two biologically active forms namely
phylloquinone (also known as vitamin K
1
)

Assessment of Menaquinones
Haemostasis 2000;30:298–307
299
and the menaquinones (known by their group
name vitamin K
2
) [2–4]. All K vitamins have
2-methyl-1,4-naphthoquinone (also known as
menadione) as a common ring structure, but
differ from each other in the length and satu-
ration degree of the polyisoprenoid side chain
attached to the 3-position. Phylloquinone is
produced by green plants, where it is tightly
associated with the thylakoid membranes of
the chloroplasts. It is a single compound con-
taining 4 isoprenoid residues (one of which is
unsaturated) in its aliphatic side chain. Mena-
quinones contain side chains of varying
length; they are designated as MK-n where n
denotes the number of isoprenoid residues, all
of which are unsaturated. Long chain mena-
quinones (MK-7 through MK-10) are exclu-
sively synthesized by bacteria [5, 6]. Mena-
dione is often added to fortified animal food
and must be converted in the liver into MK-4
before being active as a cofactor for Á-gluta-
mylcarboxylase [7, 8]. In addition, a number
of other tissues (notably pancreas, testis and
vessel wall) are capable of converting phyllo-
quinone into MK-4 [9, 10]. For these reasons
animal products (meat, dairy, eggs) may con-
tain relatively high concentrations of MK-4. It
is well known that the bacterial flora in the
colon produces large amounts of higher mena-
quinones (notably MK-10) [11], but since at
the site of synthesis absorption seems to be
unlikely, the question of whether and to which
extent the intestinal flora contributes to the
human vitamin K status is still unclear.
Warfarin and other 4-hydroxycoumarin
derivatives are antagonists of vitamin K ac-
tion and are effective antithrombotic agents
(the so-called oral anticoagulants). They block
the conversion of KO into K by inhibiting the
enzyme KO reductase, thus hampering the
recycling of vitamin K [12]. Under these con-
ditions there is a 1:1 stoichiometric relation
between KO formation and the number of
Gla residues synthesized. It is known that
25% of the patients on oral anticoagulant
treatment are not within their therapeutic
range because of fluctuating international
normalized ratio values [13]. Besides interfer-
ing drugs, age, poor compliance and concur-
rent diseases [14–18], unstable levels of anti-
coagulation are often ascribed to dietary in-
fluences, mainly fluctuating vitamin K intake
[19–23].
In absolute amounts K
1
forms well over
80% of the total amount of vitamin K in the
human diet, and most of our present knowl-
edge on vitamin K concerns K
1
. It is known,
however, that the absorption from green vege-
tables is poor and that only 10–15% of the
vitamin is bioavailable, whereas for K
2
vita-
mins this may be higher [24, 25]. Here we
present a database on both dietary forms of
vitamin K, phylloquinone and the menaqui-
nones in a wide range of foods available on
the Dutch market. Since the specimens select-
ed formed a representative sample from the
common Dutch foods the data presented here
can be used in nutritional studies in The
Netherlands. Furthermore, we compared the
efficacy of absorption of phylloquinone and
menaquinones as deduced from their serum
profiles following oral ingestion.
Materials and Methods
Materials
Phylloquinone was obtained form Sigma (St.
Louis, Mo., USA). The menaquinones (MK-4 through
MK-10) and 2,3-dihydrophylloquinone were kind gifts
from Hoffmann-La Roche (Basel, Switzerland). All
common foods were obtained at local supermarkets.
Konakion
®
(detergent-solubilized vitamin K
1
pharma-
ceutical product) was obtained from Hoffmann-La
Roche. For the nutrition experiment we used creamed
cooked spinach from Iglo Ola (Utrecht, The Nether-
lands), and natto, which was bought as a ready-to-use
product at a local oriental store. Silica Sep-Pak car-
tridges were purchased from Millipore (Milford,
Mass., USA). All other chemicals used were of the
highest analytical grade.

Age, years
300
Haemostasis 2000;30:298–307
Schurgers/Vermeer
Extraction of Food
The procedure for extraction and purification of
vitamin K from beverages and dairy produce (except
butter and cheese) was performed as described earlier
[25] using 2,3-dihydrophylloquinone as an internal
standard. Vegetables were bought as precooked deep-
frozen products. Cooked vegetables and raw fruits
were homogenized in a blender (Ultra Turrax; Janke &
Kunkel, Staufen, Germany), and processed as de-
scribed for cooked spinach [25]. Aliquots of 1 g of
cheese, butter or margarine were extracted with 4 ml of
2-propanol, 20 ng internal standard (MK-6 for marga-
rine, 2,3-dihydrophylloquinone for other products)
and 2 ml of distilled water. The mixture was homoge-
nized with a blender, warmed to a temperature of
60°C and extracted with 8 ml of hexane. Raw meat
and fish were cut into pieces, 1 g of which was supple-
mented with 2 ml of distilled water, 5 ng of internal
standard (2,3-dihydrophylloquinone) and 4 ml of etha-
nol. Homogenization took place with a blender at
room temperature, and 8 ml of hexane were used for
extraction. Bread was dried and ground to powder in
a mortar, 1-gram aliquots were supplemented with
5 ng internal standard (2,3-dihydrophylloquinone) and
4 ml of ethanol. After homogenization in a blender ex-
traction took place with 8 ml of hexane. In all cases, the
hexane phase was evaporated and redissolved in 2 ml
of hexane. After prepurification over silica Sep-Pak
cartridges the samples were ready to measure on
reversed-phase HPLC. All samples were measured in
duplicate.
Vitamin K Detection
Vitamin K was analyzed by HPLC using a C-18
reversed phase column and fluorometric detection af-
ter postcolumn electrochemical reduction as described
previously [25]. Phylloquinone and the menaquinones
were recorded in the same run. Because of the long
retention times for the long-chain menaquinones the
flow was increased from 0.5 to 1.0 ml/min at 11 min
after injection. The interday variation was 6–8%.
Human Volunteer Study
A panel of 6 male volunteers took part in this proto-
col. Their mean age was 33.5 years, and their body
mass index was 24.3 kg/m
2
(table 1). All participants
were apparently healthy, and their serum lipid profiles
were in the normal range. Neither medications nor
vitamin supplements (other than the experimental
supplements) were taken. The experimental protocol
started at 8 a.m. after an overnight fast. At that time
the participants received a breakfast containing either
a diet low in vitamin K, a similar diet with additional
Table 1.
Characteristics of the subjects
Mean SEM
33.5 2.57
Body mass index, kg/m
2
24.3 0.82
Triacylglycerol, mmol/l 0.87 0.14
Cholesterol, mmol/l 3.96 0.28
Vitamin K
Phylloquinone, nmol/l 1.48 0.19
Menaquinones, nmol/l n.d.
Mean values B SEM of 6 healthy male volunteers.
n.d. = Not detectable.
detergent-solubilized phylloquinone, or a diet contain-
ing 400 g of spinach and 200 g of natto. All diets con-
tained 30 g of fat. During the rest of the day partici-
pants were only allowed to have a lunch low in vitamin
K (toast, marmalade, bananas, apples), and to drink
orange juice and water ad libitum. After 6 p.m. and
during the rest of the experiment only consumption of
vitamin K-rich foods (spinach, broccoli, brussels
sprouts, kale, natto and cheese) was prohibited. Blood
samples were drawn by venipunctures at 0, 1, 2, 3, 4, 5,
6, 7, 8, 10, 11, 24, 48 and 72 h after start. Serum was
prepared and 1-ml aliquots were kept frozen at –80°C
until vitamin K determination. The study design was
approved by the local Medical Ethics Committee, and
informed consent was obtained from all subjects ac-
cording to the institutional guidelines.
Data Analysis
Serum vitamin K concentrations during 72 h after
oral ingestion were recorded at indicated intervals. At
each time point mean values B SE for the 6 partici-
pants were calculated and plotted as a function of time.
Blank values (no vitamin K ingested) were subtracted
throughout the study.
Results
Vitamin K Content of Various Nutrients
For the determination of dietary phyllo-
quinone and menaquinones we subdivided
common foods into six categories: meat, fish,
vegetables and fruits, dairy, oils and marga-

Assessment of Menaquinones
Haemostasis 2000;30:298–307
301
Table 2.
Mean of K vitamins (Ìg/100 g or Ìg/100 ml) in various foods
Type of food n K
1
MK-4
Meat
Beef 7 0.6 (0.6–0.7) 1.1 (0.7–1.3)
Chicken breast 7 – 8.9 (6.4–11.3)
Chicken leg 7 – 8.5 (5.8–10.5)
Pork steak 7 0.3 (0.2–0.4) 2.1 (1.7–2.4)
Pork liver 7 0.2 (0.1–0.3) 0.3 (0.3–0.4)
Minced meat 7 2.4 (2.2–2.5) 6.7 (6.5–6.7)
Salami 7 2.3 (2.1–2.5) 9.0 (8.2–10.1)
Luncheon meat 7 3.9 (3.8–4.2) 7.7 (7.4–9.1)
Hare leg 7 4.8 (4.5–5.3) 0.1 (0.0–0.2)
Deer back 7 2.0 (1.9–2.2) 0.7 (0.6–0.7)
Goose leg 5 4.1 (3.5–4.8) 31.0 (28.2–33.1)
Goose liver paste 5 10.9 (9.3–12.1) 369 (317–419 )
Duck breast 7 1.9 (1.7–2.2) 3.6 (3.3–3.9)
MK-5 MK-6 MK-7 MK-8 MK-9
–––––
–––––
–––––
– – 0.5 (0.4–0.7) 1.1 (0.9–1.2) –
–––––
–––––
–––––
–––––
–––––
–––––
–––––
–––––
Fish
Prawn 7 0.1 (0.0–0.1) –
Mackerel 7 2.2 (1.8–2.6) 0.4 (0.3–0.5)
Herring 7 0.1 (0.0–0.2) –
Plaice 7 – 0.2 (0.1–0.3)
Eel 7 0.3 (0.2–0.5) 1.7 (1.4–2.1)
Salmon 7 0.1 (0.1–0.2) 0.5 (0.4–0.6)
Fruits and vegetables
Kale 4 817 (752–881) –
Spinach 6 387 (299–429) –
Broccoli 5 156 (139–189) –
Green peas 4 36.0 (31.2–39.4) –
Sauerkraut 7 25.1 (23.8–27.5) 0.4 (0.3–0.5)
Natto 5 34.7 (31.2–36.7) –
Banana 4 0.3 (0.2–0.4) –
Apple 4 3.0 (2.7–3.4) –
Orange 4 0.1 (0.1–0.2) –
+
–––––
–––––
– ––––
– 0.3 (0.2–0.3) 0.1 (0.0–0.1) 1.6 (1.3–1.8) –
– 0.1 (0.0–0.2) 0.4 (0.2–0.6) – –
–––––
–––––
–––––
–––––
–––––
0.8 (0.6–1.0) 1.5 (1.4–1.6) 0.2 (0.1–0.3) 0.8 (0.6–0.9) 1.1 (0.9–1.3)
7.5 (7.1–7.8) 13.8 (12.7–14.8) 998 (882–1,034) 84.1 (78.3–89.8) –
–––––
–––––

302
Haemostasis 2000;30:298–307
Schurgers/Vermeer
Table 2
(continued)
Type of food n K
1
MK-4
Dairy produce
Whole milk 6 0.5 (0.4–0.6) 0.8 (0.7–0.9)
Skimmed milk 6 – –
Buttermilk 6 – 0.2 (0.2–0.3)
Whole yoghurt 6 0.4 (0.3–0.5) 0.6 (0.5–0.7)
Skimmed yoghurt 6 – –
Whipping cream 6 5.1 (4.9–5.5) 5.4 (5.2–5.6)
Chocolate 6 6.6 (6.4–6.7) 1.5 (1.4–1.6)
Hard cheeses 15 10.4 (9.4–12.1) 4.7 (4.2–6.6)
Soft cheeses 15 2.6 (2.4–2.9) 3.7 (3.3–3.9)
Curd cheese 12 0.3 (0.2–0.4) 0.4 (0.3–0.6)
Egg yolk 8 2.1 (1.9–2.3) 31.4 (29.1–33.5)
Egg albumen 8 – 0.9 (0.8–1.0)
MK-5 MK-6 MK-7 MK-8 MK-9
0.1 (0.0–0.1) ––––
–––––
0.1 (0.1–0.2) 0.1 (0.0–0.2) 0.1 (0.1–0.3) 0.6 (0.5–0.6) 1.4 (1.2–1.6)
0.1 (0.0–0.2) – – 0.2 (0.2–0.3) –
– – – 0.1 (0.0–0.2) –
–––––
–––––
1.5 (1.3–1.7) 0.8 (0.6–1.0) 1.3 (1.1–1.5) 16.9 (14.9–18.2) 51.1 (45.3–54.9)
0.3 (0.2–0.4) 0.5 (0.6–0.7) 1.0 (0.9–1.1) 11.4 (10.7–12.2) 39.6 (35.1–42.7)
0.1 (0.0–0.2) 0.2 (0.1–0.3) 0.3 (0.2–0.5) 5.1 (4.8–5.4) 18.7 (18.1–19.2)
– 0.7 (0.6–0.8) – – –
–––––
Oils and margarines
Margarine 6 93.2 (85.6–98.3) –
Butter 6 14.9 (13.2–15.9) 15.0 (13.5–15.9)
Corn oil 6 2.9 (2.7–3.1) –
Sunflower oil 6 5.7 (5.5–5.9) –
Olive oil 6 53.7 (49.9–57.2) –
Bread
Rue bread 6 0.7 (0.5–0.9) –
Wheaten bread 6 1.1 (1.0–1.2) –
Sourdough bread 6 1.0 (0.9–1.1) –
Buckwheat bread 6 3.0 (2.8–3.4) –
Beverages
Tea 4 0.3 (0.2–0.4) –
Coffee 4 – –
Orange juice 4 – –
All samples were assessed in duplicate. Values are mean values. Highest and lowest values are given in parentheses. Foods were bought from shops in
and around Maastricht. MK-10 was not detectable in any of the foods. N = Number of different samples tested; – = not detectable.
–––––
–––––
–––––
–––––
–––––
–––––
–––––
–––––
– – 1.1 (1.0–1.2) – –
–––––
–––––
–––––

Assessment of Menaquinones
Haemostasis 2000;30:298–307
303
Fig. 1.
Serum vitamin K following the oral intake of either Konakion or a meal containing
spinach and natto. The ingested Konakion contained 3.5 ÌM K
1
, the mixed meal contained
3.5 ÌM of K
1
and 3.1 ÌM of MK-7. Points represent mean values from 6 volunteers, error bars
represent SEM. [ = K
1
after Konakion; $ = K
1
after mixed meal; P = MK-7 after mixed
meal.
rines, bread, and beverages. At least three to
six different samples or brands were obtained
in various local supermarkets, and mean val-
ues for each product are given in table 2
together with their ranges for each product.
High amounts of K
1
were found in green leafy
vegetables, broccoli, sauerkraut and marga-
rines based on plant oils. Meat, fish, dairy
produce and eggs contained both K
1
and MK-
4 with relatively high MK-4 concentrations in
goose meat and liver, butter and egg yolk.
Long-chain menaquinones were mainly found
in curd cheese, hard (Dutch) and soft (French)
cheeses, probably derived from the bacterial
starter fermentation. Very rich in menaqui-
nones was the Japanese food natto, which
consists of fermented soy beans. No substan-
tial differences were found between free-range
products (eggs, chicken, meat) and those from
factory farms. The fact that fermented bever-
ages like beer and wines did not contain
detectable amounts of menaquinones is prob-
ably due to the fact that moulds do not synthe-
size menaquinones [26].
Bioavailability of K Vitamins from Food
To examine the blank values (serum vita-
min K at low vitamin K intake) 6 male volun-
teers received a vitamin K-poor breakfast
with blood sampling (up to 72 h) as indicated.
These blank values (data not shown) were
subtracted from those obtained after con-
trolled vitamin K intake. Based on the analy-
ses summarized in table 2 we have prepared
meals consisting of 400 g cooked spinach
(equivalent to 3.5 Ìmol of K
1
), 200 g natto
(3.1 Ìmol of MK-7), supplemented with corn
oil to a total fat content of 30 g. Postprandial

304
Haemostasis 2000;30:298–307
Schurgers/Vermeer
Fig. 2.
Serum vitamin K
1
and MK-7 following the separate intake of either spinach (3.5 ÌM
K
1
) or natto (3.1 ÌM MK-7). Points represent mean values from 6 volunteers, error bars
represent SEM. $ = K
1
; P = MK-7.
serum vitamin K concentrations are given in
figure 1. One week later the volunteers re-
ceived a vitamin K-poor breakfast supple-
mented with 3.5 Ìmol of Konakion. Peak val-
ues for serum vitamin K (both K
1
and MK-7)
were found at 6 h following the meal, and at
4 h after intake of the pure compound. The
very poor absorption from green vegetables
becomes clear by comparing the difference
between the curves for K
1
pure compound
and the similar amount of K
1
from spinach.
Remarkably, MK-7 from natto was absorbed
extremely well with peak values even higher
than those for detergent-solubilized K
1
. After
having reached their peak levels a rapid disap-
pearance of both K
1
and MK-7 was observed,
but MK-7 showed complex pharmacokinet-
ics, with slow disappearance during the sec-
ond part of the curve, while it remained
detectable for at least 72 h. The half-life times
for both K
1
and MK-7 between 6 and 8 h post-
prandially were about 1.5 h, whereas during
the later phases of MK-7 disappearance the
half-life time was about 50 h. To exclude
mutual interference of absorption (e.g. by
competition for the same binding protein),
the above experiment was repeated in a de-
sign in which spinach and natto were given in
two separate meals with a 1-week interval.
The serum curves are shown in figure 2 and
are comparable to those obtained after the
combined meal.
The above absorption curves were re-
peated for other foods: broccoli as source for
K
1
and curd cheese and egg yolk as sources for
higher menaquinones (MK-8 and MK-9) and
MK-4, respectively [Schurgers, unpubl. data].
In all cases it was found that K
1
absorption
from vegetables was very poor (5–10% with-
out concomitant fat intake and 10–15% if tak-

Assessment of Menaquinones
Haemostasis 2000;30:298–307
305
en together with 30 g fat), whereas menaqui-
none absorption from dairy produce and nat-
to was much better, probably almost com-
plete.
Discussion
In this paper we describe the phylloqui-
none and menaquinone content of various
foods available on the Dutch market. All K
vitamins were quantified in the same run
after a slight modification of our previously
reported procedure [25]. It was confirmed
that phylloquinone is mainly present in green
vegetables, margarins and some plant oils
such as olive oil. Since these data are similar
to those reported by others [27–29] we have
focussed on the menaquinones in food. MK-4
was present in nearly all animal products
(meat, dairy produce, eggs), but the fact that
there were no substantial differences between
game (hare, deer), free-range animals and
those from factory farms suggests that conver-
sion of menadione from fortified animal food
(used at factory farms) does not contribute
substantially to the total tissue MK-4 stores.
Rather, it seems that the major part of MK-4
in animal products originates from conver-
sion of K
1
as was also reported to occur in
rats [10]. Relatively high concentrations of
long-chain menaquinones were found in all
cheeses. As was suggested by Shearer [26],
they probably originate from bacteria present
in the starter cultures used to induce fermen-
tation. On the basis of food frequency ques-
tionnaires and the data in table 2 it has been
calculated that phylloquinone forms almost
90% of the total dietary vitamin K intake in
the Dutch population, whereas menaqui-
nones account for less than 12% [6]. Phyllo-
quinone, however, is tightly bound to the thy-
lakoid membranes of plant chloroplasts, and
the efficacy of its liberation therefrom in the
digestive tract is poor [24, 25]. This was con-
firmed in an experiment in which we com-
pared the serum concentration vitamin K
profiles after ingestion of similar amounts of
K
1
from spinach and from a detergent-solubi-
lized pharmaceutical product. To compare
the efficacy of absorption of phylloquinone
and menaquinone we have chosen a design in
which K
1
was obtained from spinach and
MK-7 from natto. In this way the molar con-
centrations of both K vitamers could be kept
similar. As is shown in figure 1, the postpran-
dial serum concentrations of MK-7 were
much higher than those of K
1
, with a peak
height difference of more than 10-fold. Both
absorption peaks occurred 2 h later than that
for the detergent-solubilized product. From
the curves obtained, it may be concluded that
the contribution of MK-7 from natto to the
total bioavailable pool of vitamin K is much
higher than estimated on the basis of intake.
Menaquinones from other sources (cheeses,
egg yolk) were absorbed with comparable effi-
cacy as was MK-7 [Schurgers, unpubl. data],
suggesting that the contribution of menaqui-
nones to the total human vitamin K status is
much higher than generally assumed, and
may equal that of K
1
.
Another remarkable difference between K
1
and menaquinones was that the former had a
disappearance curve with an apparent half-
life time of 1.5 h, whereas the long chain men-
aquinones (not MK-4) had more complex dis-
appearance curves with a very long half-life
time. Rapid clearance is consistent with the
previously reported uptake and transport of K
vitamins in chylomicrons, from where they
are cleared by the liver during the first 8 post-
prandial hours. The very long half-life times
of the higher menaquinones suggest that these
vitamers (and not K
1
and MK-4) are redis-
tributed by the liver and set free in the circula-
tion in low and high density lipoproteins. It is
well known that LDL may be present in the

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Haemostasis 2000;30:298–307
Schurgers/Vermeer
circulation for several days. The long resi-
dence times of higher menaquinones in the
circulation implies that they are available for
extrahepatic tissue uptake for much longer
periods than is phylloquinone. Both because
of their high postprandial serum concentra-
tion and their slow clearance, the importance
of higher menaquinones for extrahepatic tis-
sues such as bone and arterial vessel wall may
be underestimated if only dietary intake is
regarded. Since vitamin K-dependent pro-
teins have been reported to be involved in the
regulation of calcium deposition in bone [30]
and in the prevention of arterial calcification
[31], intake of higher menaquinones may be
important for functions of vitamin K not
related with blood coagulation.
The high efficacy of menaquinone absorp-
tion may also have consequences for subjects
on oral anticoagulant treatment. In attempts
to identify potential causes of unstable anti-
coagulation, menaquinone intake has been ig-
nored thus far. Our data demonstrate that this
is not justified. Their efficient absorption
combined with long serum and tissue half-life
times [32] suggests that menaquinones from
curd and cheese may accumulate at repeated
intake and are a potential cause of distur-
bance of anticoagulant therapy. This is even
more so for subjects consuming natto. Al-
though in general natto is not eaten by Cauca-
sians, dietary habits may survive after migra-
tion of subjects from Asiatic countries so that
hematologists in western countries may be
confronted with this unsuspected source of
highly bioavailable vitamin K.
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