**9. Bioavailability**

The Food and Nutrition Board established the RDA level for vitamin K as 65 and 80 μg for adult women and men, respectively [62]. The adequate intake of vitamin K from food sources is relative higher about 120 μg/day and 90 μg/day for men and women, respectively [63, 64]. Neonates need approximately 2–2.5 μg/day of vitamin K that progressively increases up to 30– 55 μg/day in children.

phylloquinone content were increased in extrahepatic tissues through administration of their respective supplements after deficient condition. Moreover, MK‐4 concentration was enhanced by phylloquinone administration. They also inferred that the conversion of phylloquinone in to MK‐4 in extraheptic tissues did not require the intestinal bacterial population. This conver‐ sion is purely biochemical and remain unclear thus far [72]. Optimal daily vitamin K2 especially MK‐4 intake as well as sufficient serum concentration is required to activate Vitamin K‐

Vitamin K2 Rich Food Products http://dx.doi.org/10.5772/63902 53

Progressive administration of MK‐7 momentously increased the level of plasma MK‐7; nonetheless, MK‐4 supplementation did not enhance the MK‐4 concentration in healthy individuals. Therefore, lower dose of MK‐7 (45–90 μg/day) is considered to be effective for ameliorating the physiological dysfunctions [69]. Prime circulating form of vitamin K is phylloquinone, whereas menaquinones (MK‐9 to MK‐13) are abundantly present in liver. Stored vitamin K is rapidly depleted from the body, and almost 60–70% of absorbed vitamin

Various demographic studies were carried out to estimate the level of circulating MK‐7 level in normal and unhealthy subjects. In 1990, study was conducted in London to estimate the level of MK‐7 in young and elderly normal subjects. They found that serum concentrations ranged from 0.293 to 0.328 ng/ml in healthy individuals. Jamal et al. also assessed the circu‐ lating concentration in patients with hip and vertebral fractures subjects and noticed less amount (0.039 and 0.148 ng/ml) compared to normal subjects [76]. Additionally, French young and elderly women had non‐significant varied amount of MK‐7 (0.221–0.241 ng/ml), whereas

Japanese healthy adults and vertebral fracture older women had 3.820 and 3.290 ng/ml of MK‐ 7, whereas elderly normal women had significantly higher amount of MK‐7 (6.260 ng/ml) might be due to higher consumption of natto which are rich with MK‐7. However, postmeno‐ pausal women contained less amount of serum MK‐7 (0.75–1.10 ng/ml) as compared to normal adults (1.214ng/ml). Moreover, postmenopausal women from Osaka Japan having lower bone mineral density (BMD) showed lesser amount of circulating MK‐7 than that of normal BMD

Likewise, Kaneki et al. reported the serum levels of MK‐7 in postmenopausal women from United Kingdom, Hiroshima, and Tokyo [78]. They inferred that Tokyo women had higher amount of MK‐7 as 5.26 ng/ml followed by women lived in Hiroshima 1.221 ng/ml and the lowest concentration as 0.371 ng/ml was noticed in United Kingdom population. They also reported that natto intake has positive association with serum concentration of MK‐7 in elderly women living in Tokyo, Japan. Serum MK‐7 level was maximum (7.91 ng/ml) in women that consumed natto twice or more in a week, whereas MK‐7 level was decreased as 2.81 and 0.873 ng/ml in women when the intake of natto was reduced once or less than once in a week,

K is finally lost from body through urine (20%) and faces (40–50%) [74, 75].

hip fracture old women had 0.120 ng/ml of MK‐7.

women [77].

respectively.

dependent proteins [27, 73].

**10. Demographic study**

Both active forms of vitamin K, *that is,* phylloquinone and menaquinones, have similar absorption and assimilation pattern. However, relative few studies were carried out to estimate the absorption efficiency, including transportation, distribution, and cellular uptake of various menaquinones [10, 65]. Absorbed vitamin K is transported mainly through lymphatic system in chylomicrons to the hepatic tissue which is main storage organ for long‐chain dietary forms of vitamin K [2].

Gut absorption of all dietary forms of vitamin K appears to occur through the common pathway like most of dietary lipids. Bile acids and pancreatic enzymes accelerate the solubility, emulsification, and assimilation of vitamin K into mixed micelles in digestive system. In enterocytes, vitamin K is attached with chylomicrons and enters in lymphatic circulation system. The bioavailability of vitamin K dietary forms is positively associated with dietary lipids and integrity of food matrix [66, 67].

It was reported that isoprenoid side chain length was changed during cellular uptake, transportation, and storage of long‐chain menaquinones. Variations were observed in absorp‐ tion and transportation of vitamin K dietary forms such as phylloquinone, menaquinones (MK‐4 and MK‐9) after equivalent amount administration of respective form. Postprandial plasma concentration and absorption of MKs are relatively less than phylloquinone, and its uptakes are more in tissues.

In contract to phylloquinone, which is principally fund in triglyceride‐rich lipoproteins during postprandial as well as fasting condition, menaquinones are reallocated from triglycerides‐ rich lipoproteins to low‐density lipoproteins (LDL) in and after postprandial consumption of vitamin K. Whereas shorter‐chain menaquinones, *that is,* MK‐4 were redistributed earlier and incorporated with high‐density lipoproteins (HDLs) than MK‐9. Moreover, only MK‐4 is transported via high‐density lipoproteins (HDLs) [10, 68].

The clearance of shorter‐chain menaquinones was quick, while other was detected after days in plasma. Likewise, MK‐7 has same plasma kinetics with higher half‐life of 72 h than that of MK‐4 and phylloquinone [9, 13, 69–71]. Nevertheless, no information of plasma kinetics is available of other long‐chain menaquinones. High concentration of MK‐4 was found in non‐ hepatic tissues of the body after the ingestion of phylloquinone. This might be due to the conversion of phylloquinone to MK‐4. The exact phenomenon is still unclear; however, some researchers suggested that it was converted to other menaquinones via prenylation. In this context, deuterium labeled MK‐4 was administrated to mice which are converted to MK‐4 via integral side chain removal through prenylation. Likewise, ingestion of MK‐7 also increases the serum MK‐4 level considerably [2, 12, 17, 69, 71]. Contrary, in germ‐free rats, MK‐4 and phylloquinone content were increased in extrahepatic tissues through administration of their respective supplements after deficient condition. Moreover, MK‐4 concentration was enhanced by phylloquinone administration. They also inferred that the conversion of phylloquinone in to MK‐4 in extraheptic tissues did not require the intestinal bacterial population. This conver‐ sion is purely biochemical and remain unclear thus far [72]. Optimal daily vitamin K2 especially MK‐4 intake as well as sufficient serum concentration is required to activate Vitamin K‐ dependent proteins [27, 73].
