phylloquinone , also referred to as vitamin k1 , is a compound present in all photosynthetic plants ( 1 ) .
phylloquinone is the primary dietary source of vitamin k. in general , green , leafy vegetables contain the highest known phylloquinone concentrations and contribute approximately 60% of total phylloquinone intake ( 2 , 3 ) .
as indicated in table 1 , spinach and collards , which have concomitant high concentrations of chlorophyll associated with the photosynthetic process , hence , dark leaf color have substantially higher concentrations of phylloquinone compared to the more commonly consumed iceberg lettuce , which is substantially paler , hence , lower chlorophyll concentrations .
the other plant sources of phylloquinone are certain plant oils including soybean , canola ( also known as rapeseed ) , cottonseed , and olive ( table 1 ) .
margarine , spreads , and salad dressings derived from these plant oils are important dietary sources of phylloquinone ( 4 , 5 ) .
plant oils are used for preparation of multiple mixed dishes , hence many commercially prepared foods including baked goods also contain small amounts of phylloquinone .
although multiple databases now exist that contain some phylloquinone contents of foods ( 6 , 7 ) , the most extensive analysis of phylloquinone in common foods using established food sampling protocols ( 8) are found in the united states department of agriculture ( usda ) nutrient database for standard reference ( http://www.ars.usda.gov/sp2userfiles/place/12354500/data/sr22/nutrilistsr22a430.pdf ; accessed 05.22.10 ) .
however , numbers in this table are indicative of median concentrations of all analysis for a given food in the author 's laboratory and may differ from reference because of the inclusion of unpublished data .
the commercial hydrogenation of phylloquinone - rich oils results in a transformation of phylloquinone into a hydrogenated form , 2,3-dihydrophylloquinone ( 9 ) .
as expected , trans fatty acid concentrations are highly correlated with dihydrophylloquinone concentrations ( 10 ) . in the us food supply commercial hydrogenation of plant oils was a common practice that prolonged shelf life of the oil - based products .
many foods sold in fast - food restaurants and frozen prepared products such as fast - food french fries , doughnuts , and breaded fish sticks contained high concentrations of 2,3-dihydrophylloquinone ( 5 ) ( table 1 ) .
however , with current controversy regarding the health consequences of trans fatty acid intake ( 11 ) , there have been regional trans fat bans in the us food supply .
it is anticipated that the decrease in hydrogenation of plant oils will also reduce the presence of dihydrophylloquinone in the us food supply , hence monitoring of this form of vitamin k in the food supply is warranted . unlike trans fatty acids , dihydrophylloquinone is only present in hydrogenated plant oils , hence monitoring this form of vitamin k in the food supply is a robust approach to monitoring the practice of commercial hydrogenation of plant oils .
menaquinones are the other category of vitamin k present in the food supply ( fig .
menaquinones are often referred to as vitamin k2 , which is somewhat misleading given that all menaquinones are not alike in their origin or their function .
menaquinones are primarily of bacterial origin , and differ in structure from phylloquinone in their 3-substituted lipophilic side chain .
the major menaquinones contain 410 repeating isoprenoid units indicated by mk-4 to mk-10 ; forms up to 13 isoprenoid groups have been identified .
1 ) is unique among the menaquinones in that it is not of bacterial origin .
instead , mk-4 is formed by a realkylation step from menadione present in animal feeds or is the product of tissue - specific conversion directly from dietary phylloquinone ( 12 , 13 ) . in the united states
, menadione is the synthetic form of vitamin k used in poultry feed . as such
, mk-4 formed from menadione is present in poultry products in the us food supply ( 14 ) .
however , mk-4 formed from phylloquinone is limited to organs not commonly consumed in the diet including kidney .
the exceptions are dairy products with mk-4 found in milk , butter , and cheese , albeit in modest amounts .
therefore it is unlikely that mk-4 is an important dietary source of vitamin k in food supplies that do not use menadione for poultry feed nor are rich in dairy products .
there is growing interest in the health benefits of longer - chain menaquinones , which are limited to certain foods in the food supply .
menaquinone-7 ( mk-7 ) is primarily the product of fermentation using bacillus subtilis natto and is present in a traditional japanese soybean - based product called natto .
natto contains approximately 2.5 times more mk-7 compared to the phylloquinone content of spinach ( table 1 ) .
natto also contains mk-8 and phylloquinone ( 84 and 35 g/100 g , respectively ) , although both are modest in concentration compared to mk-7 ( 6 ) .
some cheeses also contain mk-8 and mk-9 ( 6 ) , but these are dependent on cheese production practices , hence the food composition databases are limited in their ability to characterize menaquinone intake across different food supplies .
phylloquinone , also referred to as vitamin k1 , is a compound present in all photosynthetic plants ( 1 ) .
phylloquinone is the primary dietary source of vitamin k. in general , green , leafy vegetables contain the highest known phylloquinone concentrations and contribute approximately 60% of total phylloquinone intake ( 2 , 3 ) .
as indicated in table 1 , spinach and collards , which have concomitant high concentrations of chlorophyll associated with the photosynthetic process , hence , dark leaf color have substantially higher concentrations of phylloquinone compared to the more commonly consumed iceberg lettuce , which is substantially paler , hence , lower chlorophyll concentrations .
the other plant sources of phylloquinone are certain plant oils including soybean , canola ( also known as rapeseed ) , cottonseed , and olive ( table 1 ) .
margarine , spreads , and salad dressings derived from these plant oils are important dietary sources of phylloquinone ( 4 , 5 ) .
plant oils are used for preparation of multiple mixed dishes , hence many commercially prepared foods including baked goods also contain small amounts of phylloquinone .
although multiple databases now exist that contain some phylloquinone contents of foods ( 6 , 7 ) , the most extensive analysis of phylloquinone in common foods using established food sampling protocols ( 8) are found in the united states department of agriculture ( usda ) nutrient database for standard reference ( http://www.ars.usda.gov/sp2userfiles/place/12354500/data/sr22/nutrilistsr22a430.pdf ; accessed 05.22.10 ) .
however , numbers in this table are indicative of median concentrations of all analysis for a given food in the author 's laboratory and may differ from reference because of the inclusion of unpublished data .
the commercial hydrogenation of phylloquinone - rich oils results in a transformation of phylloquinone into a hydrogenated form , 2,3-dihydrophylloquinone ( 9 ) .
as expected , trans fatty acid concentrations are highly correlated with dihydrophylloquinone concentrations ( 10 ) . in the us
food supply commercial hydrogenation of plant oils was a common practice that prolonged shelf life of the oil - based products .
many foods sold in fast - food restaurants and frozen prepared products such as fast - food french fries , doughnuts , and breaded fish sticks contained high concentrations of 2,3-dihydrophylloquinone ( 5 ) ( table 1 ) .
however , with current controversy regarding the health consequences of trans fatty acid intake ( 11 ) , there have been regional trans fat bans in the us food supply .
it is anticipated that the decrease in hydrogenation of plant oils will also reduce the presence of dihydrophylloquinone in the us food supply , hence monitoring of this form of vitamin k in the food supply is warranted .
unlike trans fatty acids , dihydrophylloquinone is only present in hydrogenated plant oils , hence monitoring this form of vitamin k in the food supply is a robust approach to monitoring the practice of commercial hydrogenation of plant oils .
menaquinones are the other category of vitamin k present in the food supply ( fig .
menaquinones are often referred to as vitamin k2 , which is somewhat misleading given that all menaquinones are not alike in their origin or their function .
menaquinones are primarily of bacterial origin , and differ in structure from phylloquinone in their 3-substituted lipophilic side chain .
the major menaquinones contain 410 repeating isoprenoid units indicated by mk-4 to mk-10 ; forms up to 13 isoprenoid groups have been identified .
1 ) is unique among the menaquinones in that it is not of bacterial origin .
instead , mk-4 is formed by a realkylation step from menadione present in animal feeds or is the product of tissue - specific conversion directly from dietary phylloquinone ( 12 , 13 ) . in the united states , menadione is the synthetic form of vitamin k used in poultry feed . as such , mk-4 formed from menadione is present in poultry products in the us food supply ( 14 ) .
however , mk-4 formed from phylloquinone is limited to organs not commonly consumed in the diet including kidney .
the exceptions are dairy products with mk-4 found in milk , butter , and cheese , albeit in modest amounts .
therefore it is unlikely that mk-4 is an important dietary source of vitamin k in food supplies that do not use menadione for poultry feed nor are rich in dairy products .
there is growing interest in the health benefits of longer - chain menaquinones , which are limited to certain foods in the food supply .
menaquinone-7 ( mk-7 ) is primarily the product of fermentation using bacillus subtilis natto and is present in a traditional japanese soybean - based product called natto .
natto contains approximately 2.5 times more mk-7 compared to the phylloquinone content of spinach ( table 1 ) .
natto also contains mk-8 and phylloquinone ( 84 and 35 g/100 g , respectively ) , although both are modest in concentration compared to mk-7 ( 6 ) . some cheeses also contain mk-8 and mk-9 ( 6 ) , but these are dependent on cheese production practices , hence the food composition databases are limited in their ability to characterize menaquinone intake across different food supplies .
the current us dietary guidelines for intakes of vitamin k are 90 and 120 g / day for women and men , respectively ( 15 ) . these guidelines are termed adequate intakes ( ai ) because the institute of medicine concluded in 2001 that there were insufficient data available to generate a precise recommendation for vitamin k. the ai values for vitamin k were generated from the third national health and nutrition examination survey ( nhanes iii , 19881994 ) and based on the median phylloquinone intake in the united states for each age and gender category ( 15 ) . in the absence of abnormal bleeding associated with low vitamin k intakes among adults , it was assumed that the current intakes are adequate . however , the adequacy of intake defined by an absence of bleeding is controversial .
furthermore , the elderly report median intakes below the current ai for adults . as reviewed elsewhere ( 16 ) , there is controversy regarding biochemical measures of subclinical vitamin k deficiency and as a consequence , the true dietary requirement of vitamin k is unknown . for the purpose of this review , dietary intakes of vitamin k will be presented relative to the current ai . by comparison ,
the guidelines in the united kingdom are 1 g / kg body / day ( 17 ) and are set at 75 g / day for adult men , 60 g / day for women , aged 1829 year , and 65 g / day for women 30 years and over in japan ( 18 )
. estimates of phylloquinone intake in various populations are probably more accurate than intakes of other forms of vitamin k and there is a substantial difference in the reported intakes from a number of countries , which seems to be related to food consumption practices in different areas ( 1823 ) .
for example , the mean reported vitamin k intake of young japanese women ( mean 21.2 years , n=124 ) was about 230 g / day ( 18 ) .
the estimated phylloquinone intakes in northern china , england , and scotland were 247 , 103 , and 70 g / day , respectively ( 23 , 24 ) .
of note , phylloquinone intakes have been decreasing over the last two decades in the united kingdom , consistent with a concomitant decline in leafy green vegetable consumption ( 25 ) . based on
the nhanes iii data , the elderly ( defined as older as 71 years of age ) have median phylloquinone intakes lower than the current ai ( 89 and 79 g / day for women and men , respectively ) .
this observation supports the findings of others who have reported very low phylloquinone intakes among those in nursing homes ( 26 ) and those with alzheimer 's disease ( 27 ) .
given emerging association of low vitamin k intakes with risk of certain diseases such as cardiovascular disease and osteoarthritis ( 16 ) , the elderly present a potentially vulnerable subgroup of the population with respect to vitamin k. very little is known about the contribution of dietary menaquinones to overall vitamin k nutrition and although it has been stated that approximately 50% of the daily requirement for vitamin k is supplied by the gut flora through the production of menaquinones , there is little evidence to support this estimate ( 28 ) . in one study among adults with acute bacterial overgrowth as induced by omeprazole , menaquinones produced by these bacteria had some contribution to vitamin k status during dietary phylloquinone restriction , but not enough to restore biochemical measures of vitamin back to normal range ( 29 ) .
as previously indicated , there are regional differences in the forms and content of menaquinones in the food supply . for example
, natto is unique to a traditional japanese diet whereas the cheeses that contain high concentrations of mk-8 and mk-9 appear to be most prevalent in european dairy producing food supplies .
although there are reported menaquinone intakes , these are limited to studies from japan ( 18 ) and the netherlands ( 21 ) , and are low compared to phylloquinone intakes . in the united states , menaquinones are limited in the food supply and have not been systematically assessed .
there are surprisingly little data on the relative biological availability of different forms of vitamin k among different food sources .
furthermore , there is a growing body of literature to suggest that our understanding of vitamin k is still rudimentary in light of new developments regarding different forms .
as previously stated , phylloquinone is of plant origin , with absolute intakes being predominantly from green leafy vegetables .
phylloquinone is tightly bound to the membranes of plant chloroplasts , and is less bioavailable compared to phylloquinone obtained from plant oils and/or dietary supplements ( 30 ) .
some estimates place the absorption of phylloquinone to be 10% from plants compared to supplements ( 31 ) .
however there appear to be differences in absorption compared to the plant species , with phylloquinone obtained from broccoli and collards having greater absorption compared to spinach ( 31 , 32 ) .
similarly , and not unexpected because vitamin k is lipophilic , addition of a fat source to the meal results in higher absorption . for a more comprehensive review of vitamin k absorption
phylloquinone differs from 2,3-dihydrophylloquinone by a saturation of a single bond at the 2,3 position of the side chain ( 9 ) .
surprisingly this single substitution results in a lower absorption of dihydophylloquinone compared to an equimolar amount of phylloquinone ( 34 ) .
there is also indirect evidence of lower activity of dihydrophylloquinone as an enzyme cofactor , which currently is the only known function of vitamin k. the implications of this poor bioavailability and activity are currently unknown , although at least one study suggests a detrimental effect on bone mineral density among older adults in a community - based cohort ( 35 ) .
the potential impact of poor utilization of dihydrophylloquinone on bone health will be of little importance in the future should hydrogenated oils be removed from the food supply .
mk-7 , when administered in the form of natto in equimolar amounts to phylloquinone administered in the form of spinach , has a peak height difference of more than 10-fold compared to phylloquinone , with a half - life of 56 hours , compared to 7.5 hours for phylloquinone ( 36 ) .
whereas all forms of vitamin k appear to be initially associated with triglyceride - rich lipoproteins ( trl ) , the longer chain menaquinones including mk-7 and mk-9 are also associated with low - density lipoprotein ( ldl ) .
these preliminary data suggest that the menaquinones have different transport pathways and distribution , which has implications for transport to extra - hepatic tissue such as bone ( 33 ) . emerging studies on mk-4 challenge our current understanding of vitamin k. as demonstrated using stable isotopes , mk-4 is a conversion product of phylloquinone via the intermediate , menadione ( 37 ) .
there appears to be both local and systemic conversion to mk-4 , with the local conversion being the predominant pathway .
to add complexity to the interpretation is the observation that this conversion does not occur in all tissues . whereas the liver contains primarily phylloquinone and very long - chain menaquinones
, mk-4 is the predominant form in the brain , pancreas , and glands ( 38 ) . in terms of dietary intakes ,
mk-4 intakes are low compared to other forms of vitamin k. however , dietary phylloquinone converts to mk-4 in those tissues where mk-4 appears to be required so it is likely that low mk-4 intakes are of little consequence to health when there is adequate dietary phylloquinone available for conversion to mk-4 . in conclusion , much of our understanding of vitamin k nutrition has focused on the primary dietary source , phylloquinone .
in contrast , the menaquinones are present in the food supply , but there are limited food composition data available . as a corollary ,
estimates of intakes of menaquinones are very limited and our understanding of their role in vitamin k nutrition is not well understood .
based upon work supported by the us department of agriculture , agricultural research service under cooperative agreement no .
any opinions , findings , conclusions , or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the us department of agriculture .
 vitamin k is present in the diet in the forms of phylloquinone and menaquinones . 
 phylloquinone , which is the major dietary source , is concentrated in leafy plants and is the vitamin k form best characterized in terms of food composition and dietary intakes . in contrast , menaquinones are the product of bacterial production or conversion from dietary phylloquinone . 
 food composition databases are limited for menaquinones and their presence in foods varies by region . 
 dietary intakes of all forms of vitamin k vary widely among age groups and population subgroups . 
 similarly , the utilization of vitamin k from different forms and food sources appear to vary , although our understanding of vitamin k is still rudimentary in light of new developments regarding the menaquinones . 
Food sources
Phylloquinone
2,3-Dihydrophylloquinone
Menaquinones
Dietary intakes
Are all forms of vitamin K the same?
Conflict of interest and funding